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Topic: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: 777ER
Posted 2013-04-15 03:54:40 and read 29643 times.

Link to the original thread Lion Air 738 Ditches In Sea Short of DPS Runway (by zkokq Apr 13 2013 in Civil Aviation)

Little background information, a 1 month old B738 operated by Lion Air of Indonesia was landing at DPS on a normal flight when it struck heavy rain. The pilot is reporting he attempted to abort the landing and perform a go-around but while trying to pull up, the aircraft got pushed into the Indian Ocean at the edge of the runway against rocks. All 101 passengers and 8 crew survived

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Gonzalo
Posted 2013-04-15 04:20:49 and read 29606 times.

This is, IMHO, one of the most important posts of the Part 1, the Reply # 247 by Jetfuel member :

From Reuters :

"As the Lion Air plane was coming in to land, with an aircraft of national carrier Garuda following behind and another about to take off on the runway just ahead, the co-pilot lost sight of the runway as heavy rain drove across the windshield.

The captain, an Indonesian citizen with about 15,000 hours experience and an instructor's license, took the controls.

Between 400 and 200 feet, pilots described flying through a wall of water, according to the source. Bursts of heavy rainfall and lost visibility are not uncommon in the tropics but the aircraft's low height meant the crew had little time to react.

With no sight of the runway lights or markings, the captain decided to abort the landing and perform a "go around", a routine maneuver for which all pilots are well trained.

But the captain told officials afterwards that instead of climbing, the brand-new 737 started to sink uncontrollably.

From 200 feet, well-practiced routines unraveled quickly.

"The captain says he intended to go around but that he felt the aircraft dragged down by the wind; that is why he hit the sea," said the source, who was briefed on the crew's testimony.

Link to the full article provided by Pihero:


http://www.reuters.com/article/2013/...onesia-plane-idUSBRE93D0D720130414

And this info, also from Pihero, could be very useful :

http://en.wikipedia.org/wiki/Microburst


Rgds.
G.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: FTL360
Posted 2013-04-15 05:09:16 and read 29341 times.

A powerful microburst could have exceeded the performance capabilities, no doubt.
However I am still wondering why such heavy rainfall would not show up as bright red on their weather-radar display?
Or maybe it did and they ignored the indications?

Guess only the readouts of the CVR and blackbox will reveal the truth at the end....

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-15 05:48:41 and read 29134 times.

Quoting FTL360 (Reply 2):
I am still wondering why such heavy rainfall would not show up as bright red on their weather-radar display?
Or maybe it did and they ignored the indications?

This is exactly the question I expected : See the last paragraph of my copied post :

"There were a few clues that I considered :.

The Metars, the pictures of the present weather, the loss of the tailplane... I wondered whether this was an instance of a failed go-around ( and btw, the pilot fighting the sink rate probably lessened the impact and eventually saved the occupants ).

I wasn't ready to cite a * microburst* as a factor of the accident because the initial definition was rather strict and covering freaky instances of downdraft-with-windshear, and the presence of a **supercell**, so I researched whether it has new a definition, and as a matter of fact, yes, meteorologists have widened it to encompass phenomena happening underneath a Cb cloud.
The NOAA site is very informative but there is an article on Wiki that sums it up quite nicely :

" Simple explanation
In the case of a wet microburst, the atmosphere is warm and humid in the lower levels and dry aloft. As a result, when thunderstorms develop, heavy rain is produced but some of the rain evaporates in the drier air aloft. As a result the air aloft is cooled thereby causing it to sink and spread out rapidly as it hits the ground. The result can be both strong damaging winds and heavy rainfall occurring in the same area. Wet downbursts can be identified visually by such features as a shelf cloud, while on radar they sometimes produce bow echoes


There is an added aspect of a downburst : the air current goes down very fast and when it hits the ground, it spreads horizontally at first, before curling back toward the cloud.
So the downburst alone didn't cause the accident : the windshear, changing to a strong taiwind caused the aircraft to run out of airspeed ; forced down by the downdraft and out of energy, there was only one ending : down.

A question that I expect is : "why did they initiate and continue the approach in such conditions ?"
The answer is that Cu congestus / Cb development can happen at some incredible rate in these regions and that it can be localised on a very small area : the surfers who came to the rescue of the occupants never mentioned rain or wind in their interviews and they were very close.


[Edited 2013-04-15 05:57:09]

Lastly, another excerpt from the same article :
" As the aircraft is coming in to land, the pilots try to slow the plane to an appropriate speed. When the microburst hits, the pilots will see a large spike in their airspeed, caused by the force of the headwind created by the microburst. A pilot inexperienced with microbursts would try to decrease the speed. The plane would then travel through the microburst, and fly into the tailwind, causing a sudden decrease in the amount of air flowing across the wings. The decrease in airflow over the wings of the aircraft causes a drop in the amount of lift produced. This decrease in lift combined with a strong downward flow of air can cause the thrust required to remain at altitude to exceed what is available.


[Edited 2013-04-15 06:05:04]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-15 06:40:19 and read 28835 times.

Quoting Wisdom:
IMO an aircraft pushed to the ground is more of an icing phenomenon than it is a microburst phenomenon, because a microburst would have a significant updraft before having a downdraft and the downdraft would come at the same moment as the heavy rain instead of first the rain and 200ft or 2NM further the downdraft.

Microbursts do not necessarily have updrafts. In fact the traditional microburst taught to pilots in both US and Europe, while it may mention updrafts, does not really talk about them much, probably because simple physics would dictate them to be way less powerful than the downdrafts. Much of the energy is dissipated outwards and in any case the updrafts have a much larger volume to play with than the downdrafts.

The worries are shift from headwind to tailwind, and severe downdraft. The pilots may not have reported any updraft since it would have been slight in magnitude compared to the downdraft. Downdraft and shift to tailwind are blended phenomena; there is no clear boundary. Same with the rain. You can't make the kind of delineation you are inferring about first rain and so forth.



Regarding icing, how could they do the whole approach with the aircraft apparently behaving normally, and then suddenly when they tried to go around they sank? Sure they need more lift then but the wing would have been producing much lift thank normal on the whole approach. Methinks they would have noticed.

Quoting Wisdom:
The downdraft would be very turbulent that close to the ground but passengers didn't note any turbulence, only heavy rain.

The first updraft would be noticeable to the passengers as well, instead the passengers didn't notice any turbulence until they hit the water.


Passenger testimony is notoriously inaccurate. While they may be right they are just as likely wrong. They are not only not experts, they have only a side view and no instruments. You can't discount a microburst as a cause because the pax didn't notice it.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: mcoatc
Posted 2013-04-15 06:51:47 and read 28732 times.

Quoting FTL360 (Reply 2):
Or maybe it did and they ignored the indications?

Guess only the readouts of the CVR and blackbox will reveal the truth at the end....

Without a doubt it will be very interesting to hear the CVR, and the sequence in which the events occur. There is one thing that is glaring at me here though.....

Quoting Pihero (Reply 3):
A pilot inexperienced with microbursts would try to decrease the speed.

This is very true, but what we are hearing is a captain with 15,000 flight hours, so are we dealing with experience or complacency? I am certainly not assigning blame, but it sure seems like we are looking at an approach that should have been aborted long before it actually was.

Quoting Gonzalo (Reply 1):
Between 400 and 200 feet, pilots described flying through a wall of water, according to the source. Bursts of heavy rainfall and lost visibility are not uncommon in the tropics but the aircraft's low height meant the crew had little time to react.

This is generally not the hallmark of a visual approach now is it? While I am not familiar with the weather in Indonesia, I am familiar with similar microburst-producing storms in central Florida, which has a similar tropical climate. The cells can be unbelievably intense and yet very localized, but extreme caution must be exhibited by the crews. What is a viable visual approach can deteriorate to downright dangerous in minutes. If the airfield lacks modern weather equipment, coupled with a crew that is so used to this kind of weather that instead of using extreme caution they instead think "just another day at the office", I could easily see what transpired unfolding.

I do have a question for the pilots here. While I understand airlines make different equipment selections, I was under the impression that modern airliners all produce audible windshear alarms. Am I correct in that thinking, and how do you handle such situations? Microbursts are generally an immediate go-around, but shear seems to be more ambiguous. How does your carrier handle it?

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-15 07:09:30 and read 28639 times.

Quoting mcoatc (Reply 5):
Microbursts are generally an immediate go-around, but shear seems to be more ambiguous. How does your carrier handle it?

Not my carrier, but the CX FCOM for 330/340 states in summary for approaches:
- On a "WINDSHEAR AHEAD" warning, which is predictive, the approach MAY be continued. "in the event a positive verification is made that no hazard exists, the warning may be considered cautionary”.
- On a "WINDSHEAR" warning, which is reactive, do a mandatory go around.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Kaiarahi
Posted 2013-04-15 07:12:52 and read 28597 times.

Quoting mcoatc (Reply 5):
Quoting Pihero (Reply 3):
A pilot inexperienced with microbursts would try to decrease the speed.

This is very true, but what we are hearing is a captain with 15,000 flight hours, so are we dealing with experience or complacency?

I think Pihero was speaking in general. The captain of this flight is quoted in Indonesian papers as saying he went TOGA immediately.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: PHX787
Posted 2013-04-15 07:20:38 and read 28520 times.

From the other thread:

Quote:
It's a very sad picture indeed but might also be a lucky one, if the microburst would have been just a shy weaker they might have cleared the water and hit the end of the runway, the result would have been devastating. So perhaps the final verdict will be that they were all lucky to come away without casualties subjected to a very dangerous weather incident.
Quoting Gonzalo (Reply 1):
"As the Lion Air plane was coming in to land, with an aircraft of national carrier Garuda following behind and another about to take off on the runway just ahead, the co-pilot lost sight of the runway as heavy rain drove across the windshield.

I wanna know why the METAR Was reporting no rain at all?????

Here's the METAR from AvHerald:

Quote:
WADD 130830Z 10008KT 9999 SCT017 29/25 Q1007 NOSIG
WADD 130800Z 10009KT 9999 FEW017CB SCT017 30/26 Q1007 NOSIG
WADD 130730Z 15006KT 110V270 9999 FEW017CB SCT017 30/25 Q1007 NOSIG
WADD 130700Z 09006KT 9999 BKN017 30/26 Q1007 NOSIG
WADD 130630Z 16003KT 090V190 9999 BKN017 30/25 Q1007 NOSIG
WADD 130600Z 18007KT 9999 BKN016 30/25 Q1007 NOSIG
WADD 130530Z 18008KT 9999 SCT015 FEW016CB 30/26 Q1008 NOSIG
WADD 130500Z 19005KT 150V210 9999 BKN015 30/25 Q1008 NOSIG
Quoting 777ER (Thread starter):
Little background information, a 1 month old B738 operated by Lion Air of Indonesia was landing at DPS on a normal flight when it struck heavy rain. The pilot is reporting he attempted to abort the landing and perform a go-around but while trying to pull up, the aircraft got pushed into the Indian Ocean at the edge of the runway against rocks. All 101 passengers and 8 crew survived

Thanks for this! Please do this each time you all start a new thread.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Gonzalo
Posted 2013-04-15 07:37:48 and read 28403 times.

Quoting PHX787 (Reply 8):
I wanna know why the METAR Was reporting no rain at all?????

The METAR is limited to a specific time/space. You can have a "good" METAR at 15:00 LT, at XX 00' 00" latitude YY 00' 00" longitude, and a totally different scenario at 15:15 LT at XX 00' 05" / YY 00' 00". This TStorms and CB have a rapid and violent evolution, and you can be caught by surprise. But as Pihero is saying from the Part 1, the big question is "why did they initiate and continue the approach in such conditions ?"

Rgds.
G.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: jetfuel
Posted 2013-04-15 08:23:43 and read 27784 times.

Quoting Kaiarahi (Reply 7):
The captain of this flight is quoted in Indonesian papers as saying he went TOGA immediately.

I am still not convinced of this. I have tried to find a reliable source. I am of the personal opinion that any go around attempt was far too late and that the accident was compounded by company pressure not to go around (or else answer to the boss - thats just the way it is in Indonesia, apart from maybe GA). Further I suspect that a lower than ideal approach speed was used and that they that were already too low on final.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-15 09:10:14 and read 26965 times.

Quoting FTL360 (Reply 2):
However I am still wondering why such heavy rainfall would not show up as bright red on their weather-radar display?
Or maybe it did and they ignored the indications?
Quoting Starlionblue (Reply 4):
Regarding icing, how could they do the whole approach with the aircraft apparently behaving normally, and then suddenly when they tried to go around they sank? Sure they need more lift then but the wing would have been producing much lift thank normal on the whole approach. Methinks they would have noticed.
Quoting Starlionblue (Reply 4):
Microbursts do not necessarily have updrafts. In fact the traditional microburst taught to pilots in both US and Europe, while it may mention updrafts, does not really talk about them much, probably because simple physics would dictate them to be way less powerful than the downdrafts. Much of the energy is dissipated outwards and in any case the updrafts have a much larger volume to play with than the downdrafts.

I have been taught that a microburst's most deadly part is the moment you exit the first updraft and enter the downdraft. The first updraft would have pilots pushing down on the column to regain their approach slope and decrease the chances of recovery when they hit the invisible downdraft.

If you look at the picture you posted, this updraft is well shown. Remember that these clouds are several miles tall and in the approach phase, you are very close to the surface. The downdraft bounces against the surface and comes back up to fill the empty space of the air of the downdraft.

Here is proper aviation documentation explaining how this initial updraft is detectable and how it adversely affects the recovery during the approach.

http://www.srh.noaa.gov/jetstream/tstorms/wind.htm




This updraft is detectable, by the fact that the aircraft would suddenly be noticeably higher, even more so if the microburst is significant enough to cause an aircraft to not recover. We're talking about a brand new B737 with all its engine performance available and a very light load to go with it.
The phenomenon would also have been paired with significant turbulence, caused by the turbulent vortices of air and airspeed variations. The change in speed would be so significant that the pilot would have mentioned this. Instead, he said that despite the engines at full power, the aircraft wouldn't climb.
This to me points to a loss of lift rather than a smooth but rather powerful downdraft.

Given that to me more facts point to a loss of lift performance than a violent downdraft of a mircoburst, I will stick with my icing by freezing rain theory. The biggest factor being no passenger reports talking about the aircraft being bounced around, and the "wall of rain". However, a microburst is still a good possibility.


Freezing rain isn't detectable through the on-board WX radar.

Everybody sees what they want to see  





[Edited 2013-04-15 09:15:33]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Kaiarahi
Posted 2013-04-15 09:18:59 and read 26799 times.

Quoting jetfuel (Reply 10):
I am of the personal opinion that any go around attempt was far too late
Quoting jetfuel (Reply 10):
I suspect that a lower than ideal approach speed was used and that they that were already too low on final.

Based on?

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: AirlineCritic
Posted 2013-04-15 09:33:14 and read 26573 times.

Quoting Gonzalo (Reply 1):
"As the Lion Air plane was coming in to land, with an aircraft of national carrier Garuda following behind and another about to take off on the runway just ahead, the co-pilot lost sight of the runway as heavy rain drove across the windshield.

I am not an expert, but... you would think such rain would be visually easily visible. I understand from Pihero that these weather phenomena can developed very quickly, but if you are flying towards one in daylight, wouldn't you see? (Not the wind, the rain.)

Quoting mcoatc (Reply 5):
This is generally not the hallmark of a visual approach now is it? While I am not familiar with the weather in Indonesia, I am familiar with similar microburst-producing storms in central Florida, which has a similar tropical climate. The cells can be unbelievably intense and yet very localized, but extreme caution must be exhibited by the crews. What is a viable visual approach can deteriorate to downright dangerous in minutes. If the airfield lacks modern weather equipment, coupled with a crew that is so used to this kind of weather that instead of using extreme caution they instead think "just another day at the office", I could easily see what transpired unfolding.

  

Topic: 200 Feet MSL About 1nm Short Of The Touch Down Zon
Username: jetfuel
Posted 2013-04-15 10:47:07 and read 25490 times.

Quoting Kaiarahi (Reply 12):
Quoting jetfuel (Reply 10):
I am of the personal opinion that any go around attempt was far too late
Quoting jetfuel (Reply 10):
I suspect that a lower than ideal approach speed was used and that they that were already too low on final.

Based on?
MY personal experience.

Indonesia has low labour costs and fuel and delays to a LCC is very expensive. Look at the history of landing accidents within the country and you will see time after time accidents where a go around should have been performed. There is a culture that encourages pilots to get it right first time. Go arounds require a lot of explanation. Training is not as good as it is in developed first world countries because of the cost and the lack of a long term safety culture.

I have only looked at the radar approachs of aircraft using the same runway before and after the accident.10 knots can make all the difference if you see weather that experience tells you may be dangerous. The altitude on approach was certainly lower than I would think as ideal. If things were not stable then a go around should have been commenced well before it is reportedly commenced.

From the initial crash point it is clear that the aircraft must have been well over a kilometer from the touchdown aiming markers when the decision to initiate the go around (assuming this happened) occurred.


Study the radar, look at the approach charts (consider the distance from the touch down point to the position of initial impact) and remember if you become visual it is the pilots responsibility to remain visual at all times once below the min safe altitude - if not GO AROUND. Its basic stuff. You are taught go around at the earliest opportunity

This link may help explain "Radar data confirm the aircraft was approaching runway 09 and suggest the aircraft was about 100 feet below a 3 degrees glidepath descending at 700 feet per minute at a speed between 126 and 135 knots over ground, descending through 200 feet MSL about 1nm short of the touch down zone and 0.6nm short of the sea wall"

http://avherald.com/h?article=460aeabb&opt=4096




[Edited 2013-04-15 10:48:27]

[Edited 2013-04-15 10:49:10]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: bueb0g
Posted 2013-04-15 10:57:49 and read 25323 times.

Quoting jetfuel (Reply 14):
descending through 200 feet MSL about 1nm short of the touch down zone and 0.6nm short of the sea wall"

If the crew reports were accurate, by this point they were already in the grips of windshear so using data from that altitude you can't really draw a conclusion about the overall approach being low.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: jetfuel
Posted 2013-04-15 11:12:27 and read 25065 times.

Quoting bueb0g (Reply 15):
f the crew reports were accurate, by this point they were already in the grips of windshear so using data from that altitude you can't really draw a conclusion about the overall approach being low.

They were low before that as well if you watch the radar. Lets say 130 knots, which is 2.15 nm per minute and a descent rate of 700fpm and they have 1 nm to touch down. 1 nm will take approx 28 seconds. 28 seconds at 700fpm is 327 feet. If they were at 200 feet 1 nm out then they were approx 127 feet too low in the approach.

Two things that will save you are altitude and speed - they had neither. My (personal) opinion stands that any go around attempt was far too late, that a lower than ideal approach speed was used, and that another 100 feet of altitude on the approach may have saved them. Lets wait for the FDR

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Geezer
Posted 2013-04-15 11:24:34 and read 24897 times.

Images of Lion Air B 737-800 in sea at Bali



The new 737-800 is a write off.........but everyone onboard walked (or swam) away with no loss of life.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-15 11:26:54 and read 24841 times.

Quoting Wisdom (Reply 11):
Here is proper aviation documentation

No. This is a text for the un-initiated. The figure is all wrong in terms of scale. The aircraft depicted path is only valid with the pictured trajectory : higher and lower descent angles would see totally dfifferent phenomena. (btw, that's why I mentioned the site but did not want to confuse people with this very schematic )
The schematic Starlionblue inserted is much more professional as it brings a greater sense of height vs horizontal developments.

Quoting Wisdom (Reply 11):
these clouds are several miles tall

Not necessarily : microbursts happen in the early development stages.

Quoting Wisdom (Reply 11):
We're talking about a brand new B737 with all its engine performance available and a very light load to go with it.

How do you know ? Source appreciated.

Quoting Wisdom (Reply 11):
This updraft is detectable, by the fact that the aircraft would suddenly be noticeably higher, even more so if the microburst is significant enough to cause an aircraft to not recover

And yet, on the ADS-B read-out AvH inserted on the map, you see a constant descent at 700 ft/min, consistent with their 126 to 134 kt ground speed, and this down to 400 ft ( btw, that's a height of 230 ft )

Quoting Wisdom (Reply 11):
Freezing rain isn't detectable through the on-board WX radar.

Uhh ?

Guys ! Speculations are OK - I'm doing it myself - but should be based on some tangible evidence - or facts -. Otherwise we open the door to all sorts of polluting crazy ideas :
- fuel starvation
- On timeitis
- Crew inexperience...
This is not - absolutely not - a cut and dried investigation and everyone's participation is welcome , but theories should be more elaborate : The sign is " I think that ..... because of this..."

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: PW100
Posted 2013-04-15 11:53:00 and read 24428 times.

Quoting jetfuel (Reply 16):
They were low before that as well if you watch the radar. Lets say 130 knots, which is 2.15 nm per minute and a descent rate of 700fpm and they have 1 nm to touch down. 1 nm will take approx 28 seconds. 28 seconds at 700fpm is 327 feet. If they were at 200 feet 1 nm out then they were approx 127 feet too low in the approach

They were not low, apparently.

I thought we had already established that the low altitude was an incorrect radar altitude reading, caused by the QNH of 1007 (vs normal 1013.25). The altitude reported by the aircraft which shows up as transponder radar altitude is (apparently) not corrected for QNH deviation.

Per thread 1:

Quoting Pihero, thread 1, (Reply 72):

The reason for the 171 ft discrepancy between the radio altimeter and the *altitude* transmitted by the aircraft transponder is that it always refers to a *flight level*, based on the standard setting of 1013.2 hPa. We take, for low altitudes a ballpark value of 28.5 ft / hPa ; the QNH was 1007 hPa, so (1013 - 1007) x 28.5 = 171 ft

So it seems the aircraft was right on the intended glide path.

Rgds,
PW100

[Edited 2013-04-15 11:54:28]

[Edited 2013-04-15 11:55:13]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: AviRaider
Posted 2013-04-15 12:03:57 and read 24279 times.

Quoting Geezer (Reply 17):

Looking at the first two photos posted by Geezer, is there any reason why the Lion logo font, on the fuselage, is faded and in some places erased all together? I knew after accidents of this sort, airlines will often paint over the brand name but this looks erased in some ways.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: chrisair
Posted 2013-04-15 12:29:46 and read 23923 times.

Quoting AviRaider (Reply 20):
Looking at the first two photos posted by Geezer, is there any reason why the Lion logo font, on the fuselage, is faded and in some places erased all together?

Simple: the paint probably got wet before it was fully dried. Either that or someone did a shoddy painting job.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Kaiarahi
Posted 2013-04-15 12:43:25 and read 23747 times.

Quoting chrisair (Reply 21):
Simple: the paint probably got wet before it was fully dried. Either that or someone did a shoddy painting job.

They're decals, not paint.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: scbriml
Posted 2013-04-15 12:47:58 and read 23699 times.

Quoting chrisair (Reply 21):
Simple: the paint probably got wet before it was fully dried. Either that or someone did a shoddy painting job.

I don't think so - look at the 3rd photo, the titles on the starboard side are complete. I would guess the first two photos were taken much later and it looks like the titles have been abraded away. I could imagine sand suspended in the tidal water would do that pretty quickly.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: abrown532
Posted 2013-04-15 12:58:10 and read 23531 times.

A microburst could explain it, my opinion is it could be a similar incident to the Turkish crash in Amsterdam, that would also explain the sudden uncontrollable drop at low altitude.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: cubastar
Posted 2013-04-15 13:23:01 and read 23975 times.

Quoting Pihero (Reply 3):
A question that I expect is : "why did they initiate and continue the approach in such conditions ?"
The answer is that Cu congestus / Cb development can happen at some incredible rate in these regions and that it can be localised on a very small area : the surfers who came to the rescue of the occupants never mentioned rain or wind in their interviews and they were very close.

Absolutely Correct! From personal experience; while on a vectored long approach to land on 36R at DFW we were well in the clear and smooth just before being turned over to tower frequency. To our right, aircraft were in the clear being vectored to land on the East side of the field on 35R. We could see those aircraft to our right in the clear also. Then the FO said, Wow, look at that and pointed to a mature microburst between the two lines of landing aircraft. It was very compact but it was a textbook picture. You could see the downdraft hitting the ground, spreading out and then curling back over toward the center. The dust created by the microburst painted an exact picture. We reported it to approach control and they took immediate action.

We all should be careful of our comments until the investigation of an accident is complete. This is true of all accidents.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: cubastar
Posted 2013-04-15 13:25:41 and read 23800 times.

In addition, I might add that on such an overall nice afternoon, none of us had our radar turned on.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: hivue
Posted 2013-04-15 13:30:52 and read 24396 times.

Quoting PW100 (Reply 19):
I thought we had already established that the low altitude was an incorrect radar altitude reading, caused by the QNH of 1007 (vs normal 1013.25).

What makes you think something was wrong with the radar altimeter? The transponder apparently was reporting a non-QNH corrected flight level, so that would have been the altitude that was "erroneous." I think radar altimeters are pretty accurate at and below 2500 feet. Also, radar altimeters aren't barometric and so aren't set for QNH. The just use a radio beam bounced off the terrain.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: bueb0g
Posted 2013-04-15 13:54:51 and read 24086 times.

Quoting jetfuel (Reply 16):
They were low before that as well if you watch the radar.
Quoting hivue (Reply 27):
What makes you think something was wrong with the radar altimeter? The transponder apparently was reporting a non-QNH corrected flight level, so that would have been the altitude that was "erroneous." I think radar altimeters are pretty accurate at and below 2500 feet. Also, radar altimeters aren't barometric and so aren't set for QNH. The just use a radio beam bounced off the terrain.

You mean radio altimeter. PW100 was talking about the transponder altitude shown on radar data, which was reading off a standard QNH of 1013. You're both in agreement, you've just swapped the terms :P

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: PW100
Posted 2013-04-15 14:10:52 and read 23935 times.

Quoting hivue (Reply 27):
What makes you think something was wrong with the radar altimeter

Nothing was wrong. The reported reported altitude was simply not corrected for non-standard atmospheric conditions. That could have suggested that the plane was below glide path, while in fact in may have been exactly on the intended glidepath.

PW100

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: barney captain
Posted 2013-04-15 14:26:07 and read 23814 times.

Quoting Starlionblue (Reply 6):
Not my carrier, but the CX FCOM for 330/340 states in summary for approaches:
- On a "WINDSHEAR AHEAD" warning, which is predictive, the approach MAY be continued. "in the event a positive verification is made that no hazard exists, the warning may be considered cautionary”.
- On a "WINDSHEAR" warning, which is reactive, do a mandatory go around.

Wow, that's interesting. Our FOM is quite clear - "WINDSHEAR AHEAD" means just that, and a mandatory go-around is required. That's the beauty/intent of predictive windshear warnings, to prevent you getting in to a situation that may exceed the performance capabilities of the a/c. The only real way to insure "no hazard exists", is to fly in to it. Yikes.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-15 14:51:13 and read 23611 times.

Quoting jetfuel (Reply 16):
They were low before that as well if you watch the radar.

Please explain with figures.

Quoting jetfuel (Reply 16):
Lets say 130 knots, which is 2.15 nm per minute and a descent rate of 700fpm and they have 1 nm to touch down. 1 nm will take approx 28 seconds. 28 seconds at 700fpm is 327 feet. If they were at 200 feet 1 nm out then they were approx 127 feet too low in the approach.

Your maths are very impressive but totally unexploitable by pilots.
We are of a simpler mind : on a three degree glide slope, we go down 300 ft per nautical mile., no need to introduce times or speeds in that knowledge..
You still have to explain why / where / how they were low because the way I look at things, they came under a virtual glide path only in the last instants of the flight.

Quoting jetfuel (Reply 14):
MY personal experience.

... which of course includes shooting VOR/D approaches on an island in the Pacific, right ?

Quoting cubastar (Reply 25):
We all should be careful of our comments until the investigation of an accident is complete. This is true of all accidents.

  

Quoting bueb0g (Reply 28):
You mean radio altimeter

Both denominations are acceptable : a radio altimeter is a radar technology application.

Quoting bueb0g (Reply 28):
the transponder altitude shown on radar data, which was reading off a standard QNH of 1013.

It's more correct to say ... *off a standard setting of 1013.2 hPa*; but you're right.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-15 15:14:02 and read 23267 times.

Quoting Pihero (Reply 32):
Quoting jetfuel (Reply 16):
Lets say 130 knots, which is 2.15 nm per minute and a descent rate of 700fpm and they have 1 nm to touch down. 1 nm will take approx 28 seconds. 28 seconds at 700fpm is 327 feet. If they were at 200 feet 1 nm out then they were approx 127 feet too low in the approach.

Your maths are very impressive but totally unexploitable by pilots.
We are of a simpler mind : on a three degree glide slope, we go down 300 ft per nautical mile., no need to introduce times or speeds in that knowledge..
You still have to explain why / where / how they were low because the way I look at things, they came under a virtual glide path only in the last instants of the flight.

You both get real.

Jetfuel, obviously they were sinking towards the waters when they reached 200ft, otherwise there wouldn't have been any accident. What's so unbelievable about it? Isn't it obvious? They were in deep M$ù:ù$^=.
Why try to explain something so obvious to Pihero?

Pihero, when they were at 200 feet, they were low and they could never make up the loss in height, in fact, if I recall well, they fell into the water and split in two. Or are you saying that your experience flying into Bali suggest that there would be reason to believe that the aircraft lost 350 feet in 1 second due to some supermegahyperterraminimicropicoburst?

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: hivue
Posted 2013-04-15 15:14:37 and read 23227 times.

Quoting bueb0g (Reply 28):
You mean radio altimeter.
Quoting PW100 (Reply 29):
Nothing was wrong.
Quoting Pihero (Reply 32):
Both denominations are acceptable : a radio altimeter is a radar technology application.

Thanks. I've heard "radar altimeter" used often and forgot that the transponder info shows up on a radar screen.   

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-15 15:38:29 and read 22946 times.

Quoting bikerthai (Reply 33):
There are a couple of question I have concerning the freezing rain posibility.

1) In Indonesia, at the altitude involved, was it cold enough to have supercooled droplet to cause freezing rain. Seems counterintuitive for a tropical environment?

2) We've heard of freezing fuel line for long flights where the fuel can be at low temperature at an extended time. Was this flight long enough an at an altitude hight enough to cool the wing such that the freezing rain condition would exist?

Cumulonimbus clouds can take moisture to great heights of up to 10km. CB clouds can have tops above 10km.
Temperature drops at a standard 2°C per 1000ft or 6°C per 1000 meters.
So if you have a tropical temperature of 30°C on the ground, you could have down to -30°/-40°C at 10km.
At that altitude, the moisture in the air carried up by the CB will condense into water droplets and start falling under its weight. This can be caught up by new updraft and be taken up again, until the temperatures of the air cool down and the CB starts losing its energy and the downdrafts of cold altitude air become stronger than the updrafts of hot air from the ground.
Water droplets start falling in mass through this very cold air, at terminal velocity. These droplets will be under -10°C and dropping, without freezing because it takes time to warm them up but the subsidising cold altitude air helps them maintain that low temperature.... until they meet the aircraft's surface where they instantly turn into ice.

Ice forms on the wings, pilot thinks that wind is pushing him down while actually it's the ice reducing the aircraft's lift... that simple.

The flight was definitely long enough to cool the aircraft's surface down to well below freezing.
We're talking a metallic aircraft made of 1-5mm of aluminium skin carrying very little warm fuel in its wings, flying at 0°C and down to -45°C for longer than an hour.

[Edited 2013-04-15 15:40:03]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Gonzalo
Posted 2013-04-15 15:47:05 and read 22888 times.

Quoting bikerthai (Reply 33):
2) We've heard of freezing fuel line for long flights where the fuel can be at low temperature at an extended time. Was this flight long enough an at an altitude hight enough to cool the wing such that the freezing rain condition would exist?

Hi. If you are talking about BA038, remember that was a 777, and the main issue was the design of the FOHE ( Fuel/Oil Heat Exchangers ). The engines in that incident were RR Trent, the 738 uses different engines (CFM ), with different designs for the fuel system.

Quoting bikerthai (Reply 33):
1) In Indonesia, at the altitude involved, was it cold enough to have supercooled droplet to cause freezing rain. Seems counterintuitive for a tropical environment?

I have the same feeling.... The temperature indicated in the METAR seems to be too high to allow freezing rain development ( despite the METAR being just a picture of the moment and could have differences with the actual weather after some minutes / some miles away ).

Rgds.
G.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: AAexecplat
Posted 2013-04-15 16:03:56 and read 22765 times.

Quoting Wisdom (Reply 11):
Given that to me more facts point to a loss of lift performance than a violent downdraft of a mircoburst, I will stick with my icing by freezing rain theory.

I don't buy that theory at all. Have you been to Bali? I may stand corrected at some point but for now, I find the theory that an airplane is losing lift at 200 ft AGL due to freezing rain in Bali laughable.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-15 16:48:21 and read 22313 times.

Quoting bikerthai (Reply 33):
1) In Indonesia, at the altitude involved, was it cold enough to have supercooled droplet to cause freezing rain. Seems counterintuitive for a tropical environment?

Air is very warm. If you take a standard temperature of 15°C at sea level and a gradient of 2°C / 1000 ft, a standard tempeature is - 5°C at 10,000 ft ( FL 100 ).
In those regions, temperatures oscillate between Std + 10°C to std +15 up to some 15 - 20,000 ft and then it becomes in fact cooler than standard.
When they encountered rain, they were at a height of below 1000 ft, with then a temperature of 28°C and probably higher because there is always an inversion - temp rise as you climb instead of diminishing - over that island ( like most tropical isles ).
Therefore, speaking of the presence of supercooled drops of freeezing rain in these conditions is stretching a theory very far.

Quoting bikerthai (Reply 33):
Was this flight long enough an at an altitude hight enough to cool the wing such that the freezing rain condition would exist?

Bandoeng to Bali is a 465 Nm trip.
Let's break this flight down
- Climb to 37000 ft : 875 Nm / 17 min
- Descent ~100 Nm / 18 min
- Cruise : 465 - ( 85 + 100 ) = 280 Nm / 35 min at Mach .80 OAT estimated at - 50 °C
Total = 1h 10 min... That's not nearly enough to cold-soal the fuel.

Now, considering that they reached FL 100 at a distance of 40 Nm to the runway, with an average speed of 180 kt, they'd spent 13 minutes at positive temperatures between 28 and 30°C ; at the same time, the metalic skin of the airplane has a very very low thermal inertia and would be close to the OAT... 30°C...
Have you seen freezing that hot ?...
Some apparently have.

[Edited 2013-04-15 16:51:04]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-15 17:15:16 and read 22032 times.

Quoting Wisdom (Reply 11):
Freezing rain isn't detectable through the on-board WX radar

A misinterpretation. You can't detect that it is freezing rain per se, but you can certainly see that it is precipitation. You can deduce that it is freezing rain from the size of the returns (reflectivity) and the movement.

Quoting Wisdom (Reply 31):
This is what they teach you at all aviation ground schools in Europe and the U.S. currently.

I went to flight school in the US last fall and they teach it like Pihero explains it. And just to keep it even over the Atlantic, I am doing EASA coursework right now. Still explained how Pihero explains it. I am looking at the course material right now and there is no mention of updrafts at all.

The dangers in microburst are:
- Rapid shift from headwind to tailwind.
- Severe downdraft.

Quoting Wisdom (Reply 31):
Any airline pilot should know this, but apparently there are always exceptions.

Ad hominem attacks, and against one of the most respected pilots on a.nut? The more you do that, the less people will listen to you.


Quoting bikerthai (Reply 33):
2) We've heard of freezing fuel line for long flights where the fuel can be at low temperature at an extended time. Was this flight long enough an at an altitude hight enough to cool the wing such that the freezing rain condition would exist?

Probably not. Also don't confuse freezing rain with hoar frost caused by the freezing wing causing condensation of atmospheric moisture into frost on the wing.



Quoting PW100 (Reply 19):
I thought we had already established that the low altitude was an incorrect radar altitude reading, caused by the QNH of 1007 (vs normal 1013.25). The altitude reported by the aircraft which shows up as transponder radar altitude is (apparently) not corrected for QNH deviation.

Just to be clear for the laymen here:
- Transponder altitudes are always calibrated and set to standard conditions (i.e. 1013.25 hPa and 15C at mean sea level). They are never corrected for non-standard pressure or temperature. Flight crew don't use this data. It is transmitted to ATC for control purposes. These show pressure altitude.
- Pressure altimeters (the ones that are displayed on the instrumentation in front of the pilots) are calibrated to standard temperature lapse rate (1.98C/1000ft) and set to standard conditions if flying over the transition altitude and to local QNH (atmospheric pressure corrected to sea level using standard conditions) if flying below the transition altitude. In other words on the ground they will read correct elevation barring temperature correction. In the case of this accident, they would have been set to the QNH to DPS. By definition, thus, these show indicated altitude, which can be pressure altitude or pressure altitude corrected for non-standard pressure.
- Radar/radio altimeters are used during approach and landing and are not barometric at all. They measure the distance from the main gear to the ground (or sea) using radar technology.These show absolute altitude, which is the true altitude above terrain.

Quoting barney captain (Reply 30):
Quoting Starlionblue (Reply 6):
Not my carrier, but the CX FCOM for 330/340 states in summary for approaches:
- On a "WINDSHEAR AHEAD" warning, which is predictive, the approach MAY be continued. "in the event a positive verification is made that no hazard exists, the warning may be considered cautionary”.
- On a "WINDSHEAR" warning, which is reactive, do a mandatory go around.

Wow, that's interesting. Our FOM is quite clear - "WINDSHEAR AHEAD" means just that, and a mandatory go-around is required. That's the beauty/intent of predictive windshear warnings, to prevent you getting in to a situation that may exceed the performance capabilities of the a/c. The only real way to insure "no hazard exists", is to fly in to it. Yikes.

A CX Captain I talked to said that they MAY continue with "WINDSHEAR AHEAD", but it's not something they just do without a good evaluation of the situation. If there is any doubt at all, go around. Of course this was a three minute talk with me. I bet his training on windshear was a tad more extensive.  
Quoting AirlineCritic (Reply 13):
I understand from Pihero that these weather phenomena can developed very quickly, but if you are flying towards one in daylight, wouldn't you see? (Not the wind, the rain.)


I'm not sure. Perhaps if there are rain bands about you think "eh, just more rain".

[Edited 2013-04-15 17:53:25]

[Edited 2013-04-15 17:54:07]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-15 17:33:31 and read 21905 times.

Quoting AAexecplat (Reply 36):
I may stand corrected at some point but for now, I find the theory that an airplane is losing lift at 200 ft AGL due to freezing rain in Bali laughable.

Unfortunately, I heartily agree with you.

Quoting AirlineCritic (Reply 13):
I am not an expert, but... you would think such rain would be visually easily visible. I understand from Pihero that these weather phenomena can developed very quickly, but if you are flying towards one in daylight, wouldn't you see? (Not the wind, the rain.)

My opinion is that the cell / microburst suddenly started when they'd already passed the center of the rain + downdraft part . See Starlion diagram above. They never saw it.

Now that we've spent a few hours together, I might as well give the way I see the chain of events of this accident, and I acknowledge - I even stress it - the fact that it is still early days and I might be seriously mistaken. This is just an opinion: mine :

- Airplane was on a routine flight

- They started a VOR DME approach - the only instrument approach available for that runway - into RWY 09 in Denpasar.

- Weather was warm - 30°C - with some active convectivity with a few Cbs in the vicinity... the wind was light, shifting on an angle of some 180°.

- F/O was PF as this trip was "his". Initially, they were still in *routine mood*. Approach was stabilised, as the constant descent plane shows.

- Around 400 ft agl, they encountered a " wall of rain".
IMO, they hit the *other side* of a fast developping cell

- Captain took over the controls and attempted a go-around as they were losing height, sinking faster than they intended for the approach and getting low on the glide path.
IMO, a captain in normal situations doesn't take over control from his F/O...here, he might have sensed another degree of urgency

- Go-around wasn't successful as the capability of the aircraft was overcome by the downdraft / windshear.
IMO just a 35 to 40 kt of sudden tailwind would have taken the aircraft to stall speed...It doesn't require dramatic values

- They hit the water with a marked nose-up pitch... the breaking of the tailplane + the structural failure aft of the wing attachment helped dissipate the energy of the impact, making the accident survivable.

- The crew with the help of some witnesses did a good evacuation job.
Kudos to them

[Edited 2013-04-15 17:35:38]

[Edited 2013-04-15 17:48:09]

[Edited 2013-04-15 17:52:56]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: airtechy
Posted 2013-04-15 17:50:31 and read 21673 times.

The reading sent to the ground by an encoding altimeter is not corrected before being sent to local baro conditions. The correction is made on the ground. That's how we can have blind encoders. I believe the encoded return is only correct with a baro pressure of 29.97.

The display on the radar would be the transponder encoded return corrected for local barometric pressure.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-15 17:56:02 and read 21699 times.

Quoting airtechy (Reply 40):
The display on the radar would be the transponder encoded return corrected for local barometric pressure.

The AvH picture displays are of **FL**, i.e flight levels, hence with a standard setting of 1013.2 hPa / 29.92 inHg.

[Edited 2013-04-15 17:57:08]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: airtechy
Posted 2013-04-15 17:58:41 and read 21620 times.

Quoting Pihero (Reply 41):

The AvH picture displays are of **FL**, i.e flight levels, hence with a standard setting.

You are right ... I stand corrected.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-15 18:01:07 and read 21693 times.

Quoting Pihero (Reply 39):
MO just a 35 to 40 kt of sudden tailwind would have taken the aircraft to stall speed...It doesn't require dramatic values

35-40 sudden tailwind sounds pretty dramatic to me!       Then again in a 172 if you get 10-15 knots windshear on final the pucker factor definitely increases.

What would you call "dramatic values"?

Quoting airtechy (Reply 40):
The reading sent to the ground by an encoding altimeter is not corrected before being sent to local baro conditions. The correction is made on the ground. That's how we can have blind encoders. I believe the encoded return is only correct with a baro pressure of 29.97.

Indeed, except that standard pressure is 29.92 inHg, not 29.97. Outside North America hPa (mbar) are used in which case the value is 1013.25 hPa,

[Edited 2013-04-15 18:04:03]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: XT6Wagon
Posted 2013-04-15 18:40:57 and read 21307 times.

Quoting Starlionblue (Reply 43):
35-40 sudden tailwind sounds pretty dramatic to me!       Then again in a 172 if you get 10-15 knots windshear on final the pucker factor definitely increases.

wouldn't take even that much... Going from a 20 knot headwind to a 20 knot tailwind is the same as a sudden 40 knot tail wind.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: mercure1
Posted 2013-04-15 18:50:51 and read 21233 times.

Quoting Pihero (Reply 39):
Around 400 ft agl, they encountered a " wall of rain".
IMO, they hit the *other side* of a fast developping cell

Bad luck! right at the MAP, the straight-in MDA for Jepp chart 13-1 VOR DME RWY09, 15MAR13 is 470' MSL (459' AGL) @ apprx 2.0 DME from BLI VOR (1.5nm togo from threshold).

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Jano
Posted 2013-04-15 19:12:05 and read 21059 times.

Quoting Pihero (Reply 39):
- Go-around wasn't successful as the capability of the aircraft was overcome by the downdraft / windshear.
IMO just a 35 to 40 kt of sudden tailwind would have taken the aircraft to stall speed...It doesn't require dramatic values

Assuming all what you wrote is correct and it is really what happened. Is there any chance at all to save the flight with that much tailwind at the height they were at?

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: T prop
Posted 2013-04-15 20:23:33 and read 20447 times.

Quoting AviRaider (Reply 20):

Looking at the first two photos posted by Geezer, is there any reason why the Lion logo font, on the fuselage, is faded and in some places erased all together? I knew after accidents of this sort, airlines will often paint over the brand name but this looks erased in some ways.

Yes, that's probably what's going on, people were sent to paint over the tittles and they ran out of paint while doing the job. Some have mentioned that the livery was applied with decals or that the paint was still wet or that it was a poor paint job to begin with, this is not the case.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: AeroWesty
Posted 2013-04-15 20:31:56 and read 20443 times.

Quoting T prop (Reply 47):
Yes, that's probably what's going on, people were sent to paint over the tittles and they ran out of paint while doing the job.

Agreed. It wasn't until I clicked on the second photo that I saw the roller marks, especially on the right side of the 'n'.

Quoting Pihero (Reply 37):
Have you seen freezing that hot ?...
Some apparently have.

Thanks for your intelligent and informative posts. I've enjoyed them all.  

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: mcoatc
Posted 2013-04-15 20:56:40 and read 20195 times.

Quoting Starlionblue (Reply 43):
35-40 sudden tailwind sounds pretty dramatic to me! Then again in a 172 if you get 10-15 knots windshear on final the pucker factor definitely increases.

What would you call "dramatic values"?

I have seen 70 knot windshear values reported by my equipment, and had co-workers have 80 knot days. Values in the 30-40 knot range are daily occurrences in this area during the summer, so not as dramatic as it may sound.

Definitely not a good place to be when you're low and slow.

Quoting barney captain (Reply 30):
Wow, that's interesting. Our FOM is quite clear - "WINDSHEAR AHEAD" means just that, and a mandatory go-around is required. That's the beauty/intent of predictive windshear warnings, to prevent you getting in to a situation that may exceed the performance capabilities of the a/c. The only real way to insure "no hazard exists", is to fly in to it. Yikes.

I remember a TAM crew landing after having been issued a microburst alert that no one else would even attempt an approach in. Was it a language issue or simply a vastly different take on weather? Either way, I'm always amazed at the light precip certain crews balk at flying through and the ghastly stuff other pilots aim right at. Thanks for your info.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: s5daw
Posted 2013-04-15 23:31:26 and read 19160 times.

Quoting AAexecplat (Reply 36):
I don't buy that theory at all. Have you been to Bali? I may stand corrected at some point but for now, I find the theory that an airplane is losing lift at 200 ft AGL due to freezing rain in Bali laughable.

So, you find freezing rain in Bali laughable?

You know how they also call freezing rain? Hail. https://www.youtube.com/watch?v=Lb1w0u8xrzs

I guess the laugh is on you.

Of course, there is a difference between frozen water and supercool water, but in terms of "water below freezing point in Bali", they are the same.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-15 23:52:00 and read 19003 times.

Quoting s5daw (Reply 50):
So, you find freezing rain in Bali laughable?

You know how they also call freezing rain? Hail. https://www.youtube.com/watch?v=Lb1w0u8xrzs

I guess the laugh is on you.

Of course, there is a difference between frozen water and supercool water, but in terms of "water below freezing point in Bali", they are the same.

I'll disregard your condescending tone and stick with the facts.

You can't equate hail and freezing rain. From an both meteorological and aviation perspectives, they are very different things.

Hail can certainly damage an aircraft on impact, but importantly it doesn't stick to the plane. Ice does not stick when already formed in the air, it accretes on the airframe from supercooled droplets or moisture. Hail bounces right off. You'll get dents and maybe broken lights and radomes. Certainly nothing to sneer at but typically survivable. You won't suddenly sink because of hail.

Freezing rain is very dangerous as it can lead to rapid ice accretion, changing the shape of the airfoil, decreasing lift, increasing weight, increasing stall speed and freezing controls.

So why can you have hail on the surface in Bali but not freezing rain? Simple. Hail is formed in convective clouds and is then launched out of them. Given the size of the ice pellets they can occasionally survive all the way to the surface despite constant warming all the way down. But they were not formed near the surface. Hail must perforce be formed above the freezing level, and in the tropics the freezing level is high all year. For this reason, hail at the surface does happen in the tropics but is quite rare compared to temperate climates, and hailstones tend to be smaller.

For water droplets to become freezing rain, they must, like hail, be cooled below freezing. Again, this must happen above the freezing level. As mentioned the freezing level is very high in the tropics so this freezing rain cannot exist at the levels we are talking about in this accident. If any freezing rain escapes a convective cloud, it cannot remain below freezing like hail. It will rapidly be heated as it falls and then be just normal rain. If we take the temperature on the day of the accident to be over 30, and take even a high lapse rate of 3C /1000 feet the freezing level is 10000 feet. With a standard lapse rate the freezing level is 15000 feet but given there was convective activity it may well have been higher than standard. As Pihero also mentions, an inversion is likely, meaning even warmer temperatures at low levels.

[Edited 2013-04-15 23:52:40]

[Edited 2013-04-15 23:54:45]

[Edited 2013-04-16 00:23:46]

[Edited 2013-04-16 00:25:45]

[Edited 2013-04-16 00:31:13]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: deepunderground
Posted 2013-04-16 01:53:48 and read 18093 times.

Quoting mcoatc (Reply 5):
I am familiar with similar microburst-producing storms in central Florida, which has a similar tropical climate

You cannot really compare the two climates, to be honest.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-16 01:54:58 and read 18118 times.

Quoting Pihero (Reply 37):
When they encountered rain, they were at a height of below 1000 ft, with then a temperature of 28°C and probably higher because there is always an inversion - temp rise as you climb instead of diminishing - over that island ( like most tropical isles ).
Therefore, speaking of the presence of supercooled drops of freeezing rain in these conditions is stretching a theory very far.

Your argumentation is excellent and correct.
Your conclusion however? A temperature inversion is the characterising event of freezing rain.
You do know that right? The surface temperature doesn't matter.
If hail was formed at 30.000 feet and fell into a temperature inversion at 25.000 feet, to melt and then be cooled down by cold subsidising air at -15°C, and dropped along a column of cold subsidising air, it could well have maintained supercooling until striking the aircraft's cold wings.

Quoting Starlionblue (Reply 38):
A misinterpretation. You can't detect that it is freezing rain per se, but you can certainly see that it is precipitation. You can deduce that it is freezing rain from the size of the returns (reflectivity) and the movement.

It depends on what kind of freezing rain it is. If it's hail that melted into supercooled drops, you would be able to see it on the WX radar as shallow rain, but it depends also on the angle of the precipitation relative to the flight path.

Quoting Jano (Reply 46):
Quoting Pihero (Reply 39):
- Go-around wasn't successful as the capability of the aircraft was overcome by the downdraft / windshear.
IMO just a 35 to 40 kt of sudden tailwind would have taken the aircraft to stall speed...It doesn't require dramatic values

Assuming all what you wrote is correct and it is really what happened. Is there any chance at all to save the flight with that much tailwind at the height they were at?

No chance in hell and if it happened at 200-300ft, the huge tailwind would make the aircraft point sharply nose down, and the aircraft would probably have struck the sea nose down with many casualties

See the Delta L1011 crash sequence on youtube/

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: mandala499
Posted 2013-04-16 02:04:50 and read 18171 times.

Pihero, did you call me?    Sorry but my phone have been ringing non-stop since the accident.

Several points I've made in my head so far:
1. Note flap position, that's still landing flap configuration. What's the G/A SOP ? I'll have to check my books later.
2. Aircraft had not turned to the runway. The aircraft ended up right on the path towards the VOR as per VORDME09 approach, which brings you exactly where the aircraft ended +/- 50 meters.
3. Low energy slight nose up impact appears to be apparent. If G/A thrust had been applied and they botched it it would have been a lot messier than it is. Note that the aircraft should be quite light entering DPS as BDO has severe weight restrictions for 738 and 320s (60 something tons for 320 from what I recall, and 738s about the same).
4. Left slats clean, right slats "dented at places", right winglet broken on top. Speculation warning is hereby declared... but, this indicate left wing low water impact and right wing at one stage had submerged. Dents found on right slat if I remember correctly are on outer right slat, with possibly rock impact dents.

I've received a training profile of the Captain of the flight but I'll need to churn through it before I discuss it further.
I wanna know what the Virgin Australia 738 behind the stricken aircraft saw, he got to about 1300ft before going around.

Currently suspected it's "soft windshear"...

Mandala499

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-16 02:19:39 and read 17939 times.

Quoting mandala499 (Reply 54):
Several points I've made in my head so far:
1. Note flap position, that's still landing flap configuration. What's the G/A SOP ? I'll have to check my books later.

I noted that in the previous thread. In windshear usually the immediate priority is to TOGA and maintain flaps until you maintain safe speed and positive rate of climb. Then you decrease flaps and go gear up.
So it's not dramatic if they haven't touched on the flaps and raised the gears, in fact it would have been the correct course of action.

Quoting mandala499 (Reply 54):
3. Low energy slight nose up impact appears to be apparent. If G/A thrust had been applied and they botched it it would have been a lot messier than it is. Note that the aircraft should be quite light entering DPS as BDO has severe weight restrictions for 738 and 320s (60 something tons for 320 from what I recall, and 738s about the same).

It does. So here one has to analyse whether the aircraft could have achieved the nose up attitude given the strong downdraft and resulting tailwind component. The aircraft would certainly dive for the sea under normal CG position, regardless of pitch input.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-16 02:32:26 and read 17849 times.

Quoting Wisdom (Reply 53):
Your conclusion however? A temperature inversion is the characterising event of freezing rain.
You do know that right? The surface temperature doesn't matter.
If hail was formed at 30.000 feet and fell into a temperature inversion at 25.000 feet, to melt and then be cooled down by cold subsidising air at -15°C, and dropped along a column of cold subsidising air, it could well have maintained supercooling until striking the aircraft's cold wings.

Yes, I know all that. It doesn't alter the fact that the inversion should be present at temperatures around freezing... which is not patently the case at 400 ft ; below the cloud, they were also below the inversion ( which is the cause of *blocking* the vertical development and the aggregation of droplets into bigger drops which in turn become rain ). The falling rain, in turn *pulls* the air with it - just turn the tap in your kitchen and observe this phenomenon when the sprinkler is used . The more intense the rain, the more intense the downdraft, the more severe it becomes with a smaller cell. ( That the reason they were initially called *microbursts*).
Why microbursts are more intense in warmer areas is due to the important evaporation in the initial convective updraft that caused the formation of the cloud. The evaporation cools down the air further, accelerating the downdraft with subsidising / colder air.
The temperatures associated with the cloud ( we are talking about relatively low vertical development, and certainly not the *towering* Cbs ), are basically all positive and even very warm. You won't have hail, let alone supercooled drops in this situation.
I say it again, at 400 ft, the OAT would have been around 30°c, the skin of the aircraft well above freezing temperatures.
Call it a *hot soak*, the type we all enjoy in a relaxing bath.   

Sorry ; your theory doesn't hold a ml of water ( pun intended )

Quoting Wisdom (Reply 53):
the huge tailwind would make the aircraft point sharply nose down, and the aircraft would probably have struck the sea nose down with many casualties

They were trying to go around, with in all probability a nose-up pitch.

On this aspect, that failed go around in all probability - again, I'm careful in my speculation - reduced the rate of descent caused by the downdraft, saving all on board... the corollary is that, as a matter of possible fact, they were close to making it there... but had they climbed further, they'd hit an even stronger winsdshear and pancake closer to - or at - the airport ... with direr results.
My opinion is that in their unlucky circumstances, luck came back to help them.
That, of course, could be a lesson on how life is.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-16 02:35:02 and read 17842 times.

Quoting mandala499 (Reply 54):
Pihero, did you call me?

Welcome back, buddy !
I had also thought of that Virgin flight... and come out with nothing 'cause I don't know how far behind it was, whether they received an ATC instruction, they saw the crash ( unlikely ) or, more probably, they saw the wall of rain.
Did the preceding airplane make any PIREP on the conditions of his approach ?

[Edited 2013-04-16 02:43:29]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: zeke
Posted 2013-04-16 02:57:12 and read 17645 times.

Quoting barney captain (Reply 30):

If that is your SOP, follow it. Predictive windshield is a wx radar function, the radar cannot actually detect winshear, it uses an algorithm which assumes a vertice component based upon the horizontal components it can see. Mechanical turbulence from terrain can produce such warnings, and you are not going to fall out of the when you fly through that

Quoting s5daw (Reply 50):

Hail and supercooled water droplets are not he same, one should not use hail as evidence of the presence of supercooled water droplets. The possibility of supercooled rain on approach in Bali in my view is zero. This time of year it is normally around 20 deg c, and it the dry season.

Quoting mandala499 (Reply 54):

If they were high, had thrust back close to idle, it could have been the time to spool up being the issue. Depending on the call, winshear go, no config change I made until out of the shear.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-16 03:24:29 and read 17450 times.

Quoting Wisdom (Reply 53):
If it's hail that melted into supercooled drops,

Let's be careful with terminology. Hail cannot melt into supercooled drops. If it melts it becomes water above freezing.

Quoting Wisdom (Reply 53):
If hail was formed at 30.000 feet and fell into a temperature inversion at 25.000 feet, to melt and then be cooled down by cold subsidising air at -15°C, and dropped along a column of cold subsidising air, it could well have maintained supercooling until striking the aircraft's cold wings.

This seems highly unlikely since if the hail is shot out of the CB cloud it would fall outside it, perhaps melting but not being recooled to supercooled rain, and if it stays inside the cloud it cannot melt but keeps growing until it becomes too heavy and is, again, shot out.

In any case why do you need the hail in this scenario. The presence of hail actually makes supercooled rain less likely since it provides nuclei for ice formation.



I'll note that the experts on the thread seem to favor windshear/microburst based on current information, and they all discount icing. Not saying icing didn't happen, just that it seems an unlikely hypothesis based on current information.

Quoting mandala499 (Reply 54):
Pihero, did you call me?    Sorry but my phone have been ringing non-stop since the accident.

:D  

[Edited 2013-04-16 04:18:06]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-16 05:44:47 and read 16855 times.

Quoting mandala499 (Reply 54):
Currently suspected it's "soft windshear"...

   I love it !

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: rfields5421
Posted 2013-04-16 06:07:57 and read 16679 times.

Quoting PHX787 (Reply 8):
I wanna know why the METAR Was reporting no rain at all?????

Those METAR reports are a half-hour apart. I've seen intense thunderstorms roll through Dallas-Fort Worth - bringing all traffic at dozens of airports to a complete stop - and never appear on the METAR, because the storms move so fast.

I've also seen METAR report from DAL and ADS report winds 160 degrees apart at the same time at over 30 kts. Those airports are 7 miles apart. One reporting heavy rain with below minimums visibility, the other reporting over 10 miles visibility.

One of the factors highlighted in the investigation of Delta 191 was that even tower controllers might not have sufficient knowledge of dangerous weather for inbound aircraft on large airports without special remote sensors. The airport METAR will not provide accurate information of weather where the aircraft was located.

At DFW the issue is the physical size of the airport. DFW 191 first hit the ground about 2 1/4 miles from the tower, off the airport property, and came to rest just over 2 miles from the tower - on the airport property. It encountered the windshear and the approach began to destabilize approx 4 miles from the tower. The weather radar which DFW controllers had available to them was from a doppler radar located 72 miles away from the accident site.

Here is the weather approx 11 minutes before Delta 191 crashed

Quote:
1751 - 6,000 feet scattered, estimated ceiling 21,000 feet broken,bvisibility 11 miles, temperature 1Olv.; dew point 659.; wind 120’ atb08 knots, altimeter setting 29.92 inches of Hg.; cumulonimbus north northeast, towering cumulus northeast-south-west-north.

This weather was observed and reported by a NWS contract weather observer located at an office in the Delta maintenance hanger. His office did not have a view to the north through east quadrant - where the crash occurred. He was about 2 1/4 miles from the initial impact and final resting place. He did not observe the crash.

Here is another weather report he observed about the time of the crash and reported approx 3 min after the crash

Quote:
1805 - Special, estimated ceiling 6,000 feet broken, 21,000 feet broken, visibility 10 miles, wind 07O’at 8 knots, altimeter setting 29.92 inches of Hg., thunderstorm began 1802, north-northeast and overhead moving slowly south, occasional lightning cloud to cloud, rain showers unknown intensity north-northeast, towering cumulus northeast-southeast, west.

From the NTSB report we know the aircraft flew through a wall of water which obscured the runway and airport - yet the weather reports do not report any rain. Only the special report indicates possible rain north to northeast of the airport.

(Both quotes are from the NTSB report on Delta 191 - http://www.airdisaster.com/reports/ntsb/AAR86-05.pdf)


At Bali this flight apparently struck the water first about 2 1/4 miles from the tower. The weather which destabilized the approach likely occurred close to 3 miles from the tower. I do not know where the weather observation office and instruments are located on the Bali airport, but it is highly doubtful it is located any closer to the crash site than the tower. There are certainly not any windshear or other weather detection instruments located out in the ocean west of the airport along the flight path.

The METAR only provides a short snapshot of weather at one location. It is very common to have rain on the approach, or on part of the airport - and not be reported in the METAR.

The Approach Controller or the Tower Controller should provide pilots on approach with any special weather warnings during the final phases of flight, based on their radar information or their observations from the tower.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-16 06:22:34 and read 16625 times.

Quoting rfields5421 (Reply 61):
At Bali this flight apparently struck the water first about 2 1/4 miles from the tower. The weather which destabilized the approach likely occurred close to 3 miles from the tower. I do not know where the weather observation office and instruments are located on the Bali airport, but it is highly doubtful it is located any closer to the crash site than the tower. There are certainly not any windshear or other weather detection instruments located out in the ocean west of the airport along the flight path.

Astute observations. The runway at DPS is located on a thin strip of land with water at both ends. The weather observation instruments are most probably on land and there's not a lot of it there.

Here's a satellite view: http://goo.gl/maps/VX86K

[Edited 2013-04-16 06:25:04]

[Edited 2013-04-16 06:25:30]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: bikerthai
Posted 2013-04-16 06:28:18 and read 16569 times.

Quoting Starlionblue (Reply 51):
Of course, there is a difference between frozen water and supercool water, but in terms of "water below freezing point in Bali", they are the same.

Thanks everyone . . . I had atmospheric 101 in college, but we never went this deep.

And Wisdom . . . whether you are right or wrong, it is always good to bring up the theory and let the analysis/data point one way or the other. It is easy for experienced pilots to quickly eliminate certain posibilites, but for the rest of us, we do need a little education.


Thai

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-16 06:53:03 and read 16473 times.

Quoting bikerthai (Reply 63):
Quoting Starlionblue (Reply 51):
Of course, there is a difference between frozen water and supercool water, but in terms of "water below freezing point in Bali", they are the same.

Thanks everyone . . . I had atmospheric 101 in college, but we never went this deep.

And Wisdom . . . whether you are right or wrong, it is always good to bring up the theory and let the analysis/data point one way or the other. It is easy for experienced pilots to quickly eliminate certain posibilites, but for the rest of us, we do need a little education.

That's what I'm saying, it could be icing, it could be a microburst, it could be a downdraft caused by the heavy rain, it could be a malfunction, it could be human factors, or a combination of these.

If we're going to lay down the possibilities, we shouldn't fixate on just one likely scenario based on an unnamed Reuters analyst and the captain's report, because with the little information available, it could virtually be any of those.

I also don't say that it wasn't windshear/microburst, but that alone would not explain the B738 failing to escape from it. The B738 has quite some power, it was half-empty, and its EGPWS system will provide advance warning. I think that that analyst report on Reuters and the captain's report should be taken with some distance. The crew was clearly overwhelmed and defeated by the situation, so even a captain's report may not be accurate.

[Edited 2013-04-16 06:54:47]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-16 06:55:22 and read 16512 times.

Quoting mercure1 (Reply 45):
Bad luck! right at the MAP, the straight-in MDA for Jepp chart 13-1 VOR DME RWY09, 15MAR13 is 470' MSL (459' AGL) @ apprx 2.0 DME from BLI VOR (1.5nm togo from threshold).

Thanks, I forgot to check that fact.

Quoting rfields5421 (Reply 61):
The METAR only provides a short snapshot of weather at one location. It is very common to have rain on the approach, or on part of the airport - and not be reported in the METAR.

A very useful reminder on how sudden the phenomenon can happen. Thanks a lot.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Sligo
Posted 2013-04-16 07:07:19 and read 16398 times.

What was the decision height?

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-16 07:42:00 and read 16333 times.

Quoting Sligo (Reply 66):
What was the decision height?

The always well informed mandala499 implied in reply 54 that they shot the VOR/DME 09 approach. The Minimum Descent Altitude is 470 feet MSL (459 feet AGL). Note that since this is a non-precision approach (no glideslope guidance) there is no decision altitude but a minimum descent altitude. They are subtly different.

You can find (old but probably still valid) plates for DPS here http://www.cyberair-yssy.com/WADDALL.pdf The VOR/DME 09 approach plate profile view shows you the expected path.

Quoting Wisdom (Reply 64):
I also don't say that it wasn't windshear/microburst, but that alone would not explain the B738 failing to escape from it. The B738 has quite some power, it was half-empty, and its EGPWS system will provide advance warning.

Microbursts are more than powerful enough to bring down a new 738, half empty or not. As explained way back in thread #1 by zeke, EGPWS probably did not give any warnings until the go around maneuver began. That's not how EGPWS works. In any case, windshear prediction is nowhere near an exact science. That's a big reason crews need to be so cautious around it. If windshear could be predicted accurately it would hardly be the bugaboo it is today.

Quoting Wisdom (Reply 64):
The crew was clearly overwhelmed and defeated by the situation, so even a captain's report may not be accurate.

It is in no way clear. I'm not saying they did everything right, but you have made your verdict with with insufficient evidence.

[Edited 2013-04-16 07:43:34]

[Edited 2013-04-16 07:44:23]

[Edited 2013-04-16 07:45:28]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Garpd
Posted 2013-04-16 07:44:02 and read 16253 times.

I'm siding on the theory of severe microburst/windshear. Nothing else would explain what the pilots have reported. Sudden, obscuring rain shower and sudden loss of altitude. It sounds like a copy of the Delta 1191 incident, only this time the low speed and corrective actions taken and the relatively softer water impact seem to have directly helped prevent loss of life.

I cannot for a second entertain any icing theories. The climate in the location alone is enough to rule that out and as Pihero has so eloquently explained, iced up fuel is so remote a possibility, it's hardly worth a second thought.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: s5daw
Posted 2013-04-16 08:03:26 and read 16194 times.

Quoting Starlionblue (Reply 51):
For water droplets to become freezing rain, they must, like hail, be cooled below freezing. Again, this must happen above the freezing level. As mentioned the freezing level is very high in the tropics so this freezing rain cannot exist at the levels we are talking about in this accident. If any freezing rain escapes a convective cloud, it cannot remain below freezing like hail. It will rapidly be heated as it falls and then be just normal rain. If we take the temperature on the day of the accident to be over 30, and take even a high lapse rate of 3C /1000 feet the freezing level is 10000 feet. With a standard lapse rate the freezing level is 15000 feet but given there was convective activity it may well have been higher than standard.

Rain drop has terminal velocity of about 10m/s. That gives a droplet 300s = 5 minutes to go from 10k feet to 0.

Water's specific heat is 4.187 kJ/kgK
Air has specific heat of 1.0 kJ/kg.K

I guess somebody could calculate the time it takes to heat the raindrop? I don't know how to 

BTW: specific heat of ice is only 2 kJ/kgK - half LESS than water. Ice heat's FASTER than water! And from experience I can tell hail stays around for longer than 5 minutes in sumer...

I'm not saying that's what happened. But if there is a rare occasion it could happen, we need to stay open so we could prevent similar accidents. Remember AF447? Pitots were not supposed to freeze at that level, right?

[Edited 2013-04-16 08:05:06]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: travelavnut
Posted 2013-04-16 08:22:34 and read 16106 times.

Quoting Wisdom (Reply 64):
That's what I'm saying, it could be icing, it could be a microburst, it could be a downdraft caused by the heavy rain, it could be a malfunction, it could be human factors, or a combination of these.

Quoting Wisdom (Reply 64):
The crew was clearly overwhelmed and defeated by the situation, so even a captain's report may not be accurate.

You're contradicting yourself here. I think it would be wise (he...he...he) to refrain from judgement until the final report comes out.

[Edited 2013-04-16 08:23:36]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-16 08:55:34 and read 15997 times.

Quoting s5daw (Reply 69):
I'm not saying that's what happened. But if there is a rare occasion it could happen, we need to stay open so we could prevent similar accidents. Remember AF447? Pitots were not supposed to freeze at that level, right?

Fair point, and I don't think any of the experts on this thread (myself certainly not in that number) are excluding any causes right now. This thread is speculating on what seems to have happened, and early indications certainly don't seem to point at icing.

The truth is left to the official investigators.

I would note in this context that a.nut discussions on AF447 were rather close to the truth at the time, at least if you knew which commenters to pay attention to.

Quoting s5daw (Reply 69):
I guess somebody could calculate the time it takes to heat the raindrop? I don't know how to 

BTW: specific heat of ice is only 2 kJ/kgK - half LESS than water. Ice heat's FASTER than water! And from experience I can tell hail stays around for longer than 5 minutes in sumer...

I don't know how to either, but I'm glad someone is at least attempting the math.   Note that changing state from frozen to liquid takes a lot more heat than it takes to change cold ice to slightly warmer ice. For every gram of ice to change to liquid, without even changing temperature at 0 degrees, you need to add 80 calories of heat. So the math is not quite as simple as we would wish. It may take ice less time to heat than water, but for it to actually become water a lot of heat needs to be added.

Incidentally, the opposite transition (liquid to solid) is the main reasons that freezing rain is so dangerous. It hits the wing, part of it freezes but in so doing every gram releases 80 calories of heat, which raises the temperature. The rest of the rain runs back along the wing and freezes further back, and then the process repeats. And then the wing is covered in ice and your whole day is ruined. But that seems like an unlikely scenario in this case.

[Edited 2013-04-16 08:56:50]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Gonzalo
Posted 2013-04-16 09:04:36 and read 15938 times.

Quoting rfields5421 (Reply 61):
The Approach Controller or the Tower Controller should provide pilots on approach with any special weather warnings during the final phases of flight, based on their radar information or their observations from the tower.

There is another very important source for the weather reports, the PIREP's. It would be very nice to know if the crew of the preceding aircraft ( Virgin Australia 737 I believe ) did any kind of warning or communication when they landed...


Rgds.
G.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: TheRedBaron
Posted 2013-04-16 09:23:14 and read 15863 times.

Year ago there was a Column on the Airways magazine, were a Captain used to write all kind of experiences, If I remember correctly is last name is Drury...anyways if memory serves correctly, he described landing on a DC 10 Freighter on Manila airport and that the approach was perfect, even sunny but as soon as he got on finals all hell broke loose and he landed and the rain and down draft has super severe, he advised immediately the guys behind him about the changing conditions OVER THE AIRPORT, and advised a go around or landing as fast and at a high speed since wind-shear was most likely present, de described the 737 entering fast, performing a go around and sinking fast and avoiding tragedy by mere meters from the tarmac.... he said that on the cockpit you should expect the unexpected in areas of the world where weather is unpredictable and changes rapidly.

My guess is that they were really close to landing, had an rather narrow window of power / lift, and the weather stalled the 738, they applied go around power but it was too late, I bet the engines were begining to spool up when they hit the water, because if they gained 20 to 30 knots while falling the kinetic energy would have made the accident a lot worse...

I guess the report will bring a lot of info on this, and the crew reacting to this dire scenario ....

Thanks for the wonderful info on weather and tech ops guys.

TRB

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: s5daw
Posted 2013-04-16 10:19:25 and read 15623 times.

How about this: apparently NASA has done some tests of effect of heavy rain on lift... and supposedly the results showed heavy rain can actually stall the airplane.

http://news.google.com/newspapers?ni...&sjid=BBUEAAAAIBAJ&pg=6649,5379775

http://crgis.ndc.nasa.gov/crgis/images/b/b7/89-102.pdf

Both, passengers and pilots described unusually heavy rain. The pilot mentioned a "wall of water" and a passengers says:

"Then suddenly, a cloud enveloped us. Torrents of water were pouring on us, it was an enormous downpour. It only lasted two, three minutes.

"It was almost as if it was night, even though the sun had been shining just before," said Grandy.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: travelavnut
Posted 2013-04-16 10:22:51 and read 15604 times.

Quoting s5daw (Reply 78):
"Then suddenly, a cloud enveloped us. Torrents of water were pouring on us, it was an enormous downpour. It only lasted two, three minutes.

"It was almost as if it was night, even though the sun had been shining just before," said Grandy.

Where was this mentioned? AvHerald writes;

Passengers reported there was no indication of any problem, no engine problems or the like and no call out from the crew, prior to impact with water."

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: s5daw
Posted 2013-04-16 10:39:16 and read 15552 times.

Quoting travelavnut (Reply 79):
Where was this mentioned? AvHerald writes;

Passengers reported there was no indication of any problem, no engine problems or the like and no call out from the crew, prior to impact with water."

I don't knwo about the original source, but it's quoted all over the media:

http://www.theaustralian.com.au/trav...r-jet/story-e6frg8ro-1226621310661

http://www.asiaone.com/News/Latest%2.../Story/A1Story20130415-416125.html

Google will show many more...

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: travelavnut
Posted 2013-04-16 10:42:21 and read 15641 times.

Quoting s5daw (Reply 80):
I don't knwo about the original source, but it's quoted all over the media:

Didn't catch that, thanks!

Maybe a stupid thought, but could rain be so localized that an observer, at the airfield for example, doesn't notice it?

[Edited 2013-04-16 10:43:39]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: TheRedBaron
Posted 2013-04-16 10:52:36 and read 15617 times.

This proves that the whole ordeal was so fast that there was no crew or pax warnings from the cockpit....

YOU ARE SEATED SEEING out everything looks normal, then heavy rain, then you feel the plane going down fast, 3 seconds later you are in the water and witnessing a really fast deceleration, and thats it....

Its great there were no casualties  

TRB

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-16 11:13:11 and read 15587 times.

Quoting s5daw (Reply 78):
pparently NASA has done some tests of effect of heavy rain on lift.

... it lead to the conclusion that the 737 classic was the most affected -because of the leding edge device close to the fuselage. It lead to operators increasing Vref by 10 kt in heavy rain.
The NG and the 738 airfoils are very different and seem not to be as affected.
But all airfoils are affected by this phenomenon. One has just to be more careful and vigilant.

Quoting travelavnut (Reply 77):
I realize eyewitness accounts can be unreliable, but judging if there is rain or not seems quite straightforward, doesn't it?

Some psychologists have tried to understand why they're not reliable and the factors are multiple : concentration on one aspect of the event, desire to be recognised and quoted in the media, pure invention...
The absence of rain observation could be explained by :
- the rain doesn't hit the ground
- the rain is now *behind* the aircraft
- the rain is there, but get psychologically discarded because eyewitness isn't been soaked
- there is actually no rain...
- ...............................................................................etc.........................................................................

"EGPWS predictions are a very exact science."
they are, unfortunately, not : just witness the different SOPs different airlines use in this respect : some demand a mandatory go aroud, some not...

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: web500sjc
Posted 2013-04-16 11:39:05 and read 15420 times.

Quoting TheRedBaron (Reply 78):
YOU ARE SEATED SEEING out everything looks normal, then heavy rain, then you feel the plane going down fast, 3 seconds later you are in the water and witnessing a really fast deceleration, and thats it....
Quoting s5daw (Reply 74):
Both, passengers and pilots described unusually heavy rain. The pilot mentioned a "wall of water" and a passengers says:

"Then suddenly, a cloud enveloped us. Torrents of water were pouring on us, it was an enormous downpour. It only lasted two, three minutes.

obviously there are reports of rain, the question is:

1) did the pilots see the rain shaft and continue to fly into the weather / wall of water?

2) did the rain shaft fall on the airplane from above (I don't know how many mirrors you have to break for that bad luck)?

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: bikerthai
Posted 2013-04-16 11:52:43 and read 15381 times.

Two questions.

1) For all practical purpose, we assume that the water is incompresible. But, does a microbust over water react differently than a microburst over land? I.E. some of the energy could be transfered into the waves (perhaps an insignificant amount)?

2) Even if there is no land at the end of the runways, are there lights on buoys (or piers) that extends into the sea? If there are, then do they extend far enough to mount sensors that may capture wind direction (at least for the most critical location near the runway).


bt

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-16 12:18:16 and read 15344 times.

Quoting bikerthai (Reply 81):
does a microbust over water react differently than a microburst over land? I.E. some of the energy could be transfered into the waves (perhaps an insignificant amount)?

an intriguing scenario. I'll lookk it up.

Quoting bikerthai (Reply 81):
Even if there is no land at the end of the runways, are there lights on buoys (or piers) that extends into the sea?

There is nothing of these sorts on Bali 09 : protection of the coral reef is the reason ; there aren't even an approach lighting system, which is why this approach should be flown with a lot of vigilance.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: FltAdmiralRitt
Posted 2013-04-16 15:28:35 and read 15016 times.

So from a Salvage point of view. Just what is valuable that is left in the
wreckage? besides the metal I mean.
Emergency Ox System, maybe the IFE system/equipment.

What about the engines any salvage value, maybe the cockpit can be recycled into a simulator?
Is there value in getting the wreckage off the water ASAP, in terms of salvage?

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: mandala499
Posted 2013-04-16 15:32:18 and read 15119 times.

Quoting Pihero (Reply 82):
There is nothing of these sorts on Bali 09 : protection of the coral reef is the reason ; there aren't even an approach lighting system, which is why this approach should be flown with a lot of vigilance.

Yeah, heard too many "how come the PAPIs are all red all of a sudden" stories on that one!   

Update:
I am now getting reports that at least 2 aircraft ahead of the accident aircraft reported windshear and went around. I am checking it up.

Quoting Pihero (Reply 60):
I love it !

In our lingo the "soft" is the one that doesn't make the plane scream out "windshear windshear"...   

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: bueb0g
Posted 2013-04-16 16:27:39 and read 14900 times.

Quoting mandala499 (Reply 84):
In our lingo the "soft" is the one that doesn't make the plane scream out "windshear windshear"...

Would that mean it wouldn't normally be enough to down an airliner then, or is it not specifically related to severity?

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: RickNRoll
Posted 2013-04-16 17:05:27 and read 14807 times.

Quoting Starlionblue (Reply 71):
I would note in this context that a.nut discussions on AF447 were rather close to the truth at the time, at least if you knew which commenters to pay attention to.

  

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-17 02:56:21 and read 14135 times.

Quoting s5daw (Reply 74):
How about this: apparently NASA has done some tests of effect of heavy rain on lift... and supposedly the results showed heavy rain can actually stall the airplane.

This is the conclusion of a study :
"The experimental data of the heavy rain effect on aircraft is not much available, because the experimentation to include rain effects is very difficult, and expensive to conduct, so it is easy and better to simulate numerically the rain effects on different kinds of airfoils and wings. For NACA 64210 ... the L/D degradation reaches up to 28% for AOA 10°.

.This is a big loss in aerodynamic efficiency... For NACA 64210 airfoil the lift and drag coefficients of numerical
simulation agrees well with the experimental results. The L/D degradation in average shows more consistency with the
experiment. ..
"
It's a lot more important t(han people would think.
The link here on WASET
It is not necessary to follow the maths : concentrate on the schematics that are their illustration and conclusion.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-17 05:37:56 and read 13733 times.

Quoting Pihero (Reply 87):
the L/D degradation reaches up to 28% for AOA 10°.

Wow. That's a lot of percent. Ouch.         

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: flyingturtle
Posted 2013-04-17 06:04:42 and read 13617 times.

Quoting Pihero (Reply 87):

Question d'un débutant:

Doesn't rain make the air more dense, and thus create more lift?

If it does not, why?


David

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: bikerthai
Posted 2013-04-17 06:22:20 and read 13558 times.

Quoting FltAdmiralRitt (Reply 83):

So from a Salvage point of view. Just what is valuable that is left in the

Probably not much could be used other than in a static non-working display in a museum.

Most of the equipment is air cooled and have been subjected to salty air for how long?

Is it even worth to ship the airframe to a recycle facility or just take it to the local yard, take out the valuable metals and boxes and burry the rest on the Island?

Or they can take what's left of the fuselage and make a hotel room out of it - like they did in Costa Rica.

bt.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-17 06:36:26 and read 13498 times.

Quoting flyingturtle (Reply 89):
Doesn't rain make the air more dense, and thus create more lift?

Yes rain makes air more dense.

However, and with the caveat that I haven't read the study, it can break up the boundary layer. Gliders especially lose massive amounts of lift in the rain due to (IIRC) highly optimized laminar flow wings.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-17 08:17:36 and read 13285 times.

Bikerhai, Lift typically increases but drag increases faster. Hence L/D ration decreases.
Thrust/Weight ratio is of equal significance if we want to consider performance.

High BPR engines will provide more thrust in rain, thanks to the increased density and better cooling performance. The only risk is flame-out, that's why you can select continuous ignition.

The study provided is inadequate in the sense that if you want to prove something you can prove it.
They were similating a given airfoil at a given airspeed (less than 100km/h by the way), and given water flow, which provided given results.

Unless they did it with a B738 wing at the approach speeds and the same precipitation rate+volume, the study isn't adequate to prove anything but a possible outcome.

At the typical approach speed of 140kts, or twice the speed than in the experiment, the boundary layer won't let many droplets come into contact with the airfoil. Instead, they will come to increase the density of the boundary layer and energise it, increasing lift.
Drag will increase on the wing and any aircraft parts facing incoming air.
L/D is more likely to decrease than increase, but again it has to be tested separately if you want a result.

On the other hand, thrust available will increase and so will the apparent weight.
Thrust will increase as the density of the air by-passing the core and being accelerated by the fan will increase, and for the air going into the core, the air entering the combustion chambers will be denser and provide better cooling to the turbines, enabling higher N1/N2 for the same EGT.

But will thrust increase enough? How will the apparent weight be affected?
No way to know unless you can test it out in the same circumstances.

Hence, it's impossible to know for now if this contributed.
Mentioning another study is most irrelevant.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: n471wn
Posted 2013-04-17 08:41:26 and read 13191 times.

Will it be possible to salvage the engines and rebuild them?

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: liquidair
Posted 2013-04-17 09:31:08 and read 13061 times.

I'm curious about something, not necessarily linking it to this accident but...

How much water can an engine ingest before it starts losing efficiency?

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-17 10:36:11 and read 12963 times.

Quoting liquidair (Reply 94):

I'm curious about something, not necessarily linking it to this accident but...

How much water can an engine ingest before it starts losing efficiency?

An appropriate question given your airliners.net username.  
An engine can ingest a lot of water before it starts losing efficiency. The point where you could say that it starts to lose efficiency is when the combustion process starts to be affected. However, if your EMC/FADEC allows it, your fuel pumps can support it, and your continuous ignition has a high enough frequency, this could be very high, as you could compensate it with more fuel and more sparks. The water/air mixture will reach several hundreds of degrees at the exit of the compressor and before the combustion chamber, so it will be mostly steam.
I don't say that you could submerge half of the core but still.

In the era of the B707, they used to carry out water ingested take-offs, to increase thrust during the take-off.
The working was double, because it increased both the density of the air, hence also the EPR and also allowed higher RPM for the same EGT, just as I described above.


The engine nor other parts are salvageable. Salt water + metals = scrap.
The engines would also be so damaged after the crash that there would be nothing worth salvaging.
If a museum is ready to pay for it, you could sell it. There are parts that can be made functional again, such as MLG retraction, it could be a nice attraction in a museum.

[Edited 2013-04-17 10:38:34]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: hivue
Posted 2013-04-17 11:38:18 and read 12755 times.

Quoting liquidair (Reply 94):
How much water can an engine ingest before it starts losing efficiency?

IIRC the fire brigade had to pump a huge amount of water into the #1 engine on the Qantas A380 at Singapore to get it to shut down.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: PW100
Posted 2013-04-17 12:09:46 and read 12666 times.

Quoting Wisdom (Reply 92):

Careful with what you state . . . .

Quoting Wisdom (Reply 92):
Thrust will increase as the density of the air by-passing the core and being accelerated by the fan will increase . . .

If air going into the fan increases in density, then the fan will have to work harder to get the same acceleration. So more work will have to be provided by the turbine. That needs to be commanded by the Fuel Control. And I'm not sure if that will happen, as the engine power output is probably balanced around engine pressure ratio (EPR), amongst many other inputs. The denser air will also effect the EPR, and the fuel metering schedule will probably balance everything out quite nicely. So I expect that entering heavy rain will not have very noticeable effects on engine thrust.

Quoting Wisdom (Reply 92):
. . . and for the air going into the core, the air entering the combustion chambers will be denser and provide better cooling to the turbines, enabling higher N1/N2 for the same EGT

Nothing factually wrong here, just the preceding conclusion.
The engine power is not controlled through EGT. EGT is just a result of the requested power output, not vice versa.
Same applies to a lesser extent for N1/N2 speeds. Although I do expect that both N1 and N2 will have a back feed to the fuel metering schedule, I expect the important parameter for thrust to be EPR.

Do notice that I use the word expect, since the CFM56 or V2500 are not my field of speciality, so I’m not really familiar with the fuel metering schedule and control logic on these engines. I’m more into turboprops, especially certain P&WC products - hence my username . . .

As for the PW100 engine family, it is mainly controlled through EPR (or better P3 air), Torque, and NH spool speed. Heavy rain will not have a noticeable effect on output power in terms of Tq or (E)SHP.

Rgds,
PW100

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-17 12:42:08 and read 12587 times.

Quoting PW100 (Reply 97):
Quoting Wisdom (Reply 92):
. . . and for the air going into the core, the air entering the combustion chambers will be denser and provide better cooling to the turbines, enabling higher N1/N2 for the same EGT

Nothing factually wrong here, just the preceding conclusion.
The engine power is not controlled through EGT. EGT is just a result of the requested power output, not vice versa.
Same applies to a lesser extent for N1/N2 speeds. Although I do expect that both N1 and N2 will have a back feed to the fuel metering schedule, I expect the important parameter for thrust to be EPR.

You are correct, I think that you're misunderstanding my statement though.
EGT is the main limiting factor for N1/N2. Add water to the mix and you will have a lower EGT for the same N1/N2. Your FADEC will take EGT into account for calculating the max N1 available at any given time, so it will translate into more N1 available when you firewall the power levers.

Quoting PW100 (Reply 97):
Quoting Wisdom (Reply 92):
Thrust will increase as the density of the air by-passing the core and being accelerated by the fan will increase . . .

If air going into the fan increases in density, then the fan will have to work harder to get the same acceleration. So more work will have to be provided by the turbine. That needs to be commanded by the Fuel Control. And I'm not sure if that will happen, as the engine power output is probably balanced around engine pressure ratio (EPR), amongst many other inputs. The denser air will also effect the EPR, and the fuel metering schedule will probably balance everything out quite nicely. So I expect that entering heavy rain will not have very noticeable effects on engine thrust.

That's correct and that additional power will be provided by higher EPR from the denser air going into the core. This will of course be achieved through higher fuel flow.

The larger the BPR, the better in water, because the additional work required by the fan wil be compensated by the higher power available thanks to the denser air flowing into the core.

The lower the BPR, the lower the effect because even though the core has more power available, it will transmit it much less efficiently into an acceleration than if it has a large fan.

The ECU will allow it as long as it feels that the EGT isn't an issue and the cooling effect will be so great that you may even get a few % of additional N1 on top of the additional work done by the core (transmitted to the fan) for the same N1.
The N1 and the fuel flow aren't directly correlated as there are many variables including air density, static pressure, dynamic pressure and the limiting EGT factor.
There are however margins that the ECU needs to monitor, to make sure that it's providing the right amount of fuel for the given parameters. (used to be done by HMU's).
In very simplistic terms, the ECU will try to maintain a given air/fuel mix, so given all other parameters constant, the denser the air, the more fuel it will allow to be pumped in.

[Edited 2013-04-17 12:45:05]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: liquidair
Posted 2013-04-17 13:00:39 and read 12494 times.

Quoting Wisdom (Reply 95):

Thanks for the explanation... I had no idea about the 707!

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: PW100
Posted 2013-04-17 13:01:34 and read 12503 times.

While this is corrrect

Quoting Wisdom (Reply 98):
Your FADEC will take EGT into account for calculating the max N1 available at any given time . . .

this may not

Quoting Wisdom (Reply 98):
. . . so it will translate into more N1 available when you firewall the power levers

You may very well hit other limits (N1, N2, EPR) before you max out on EGT.

But that is not what you initially claimed:

Quoting Wisdom (Reply 92):
Thrust will increase as the density of the air by-passing the core and being accelerated by the fan will increase, and for the air going into the core, the air entering the combustion chambers will be denser and provide better cooling to the turbines, enabling higher N1/N2 for the same EGT

Actual thrust does not increase. Thrust is increased by pushing the Power Levers, or activating TOGA.

Quoting Wisdom (Reply 98):
the ECU will try to maintain a given air/fuel mix

I don't think that is correct. In fact I'm pretty sure of it. The ECU will try to maintain constant (requested) power, and has all sorts of inputs to verify just that. Air/fuel mix is just an indirect result of all the inputs and outputs.

Rgds,
PW100

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: rcair1
Posted 2013-04-17 14:11:10 and read 12328 times.

Quoting liquidair (Reply 94):
How much water can an engine ingest before it starts losing efficiency?

The Taca 110 investigation is interesting reading in this regard. It, btw, was the same engine as this case.
One learning was that the amount of water that can be handled is quite dependent on thrust setting. When the engines are wound up more - most if not all of the water is diverted around the core - so the fire stays hot. Yes, there is water in the bypass and that impacts performance, but the engine does not go out. In the Taca case, lower throttle settings let more water go into the core and the engines flamed out. Something like that is not an unlikely factor here. A much higher probability than, for instance, icing (IMO).

Quoting hivue (Reply 96):
IIRC the fire brigade had to pump a huge amount of water into the #1 engine on the Qantas A380 at Singapore to get it to shut down.

Yes - that is correct. It ran for hours.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-17 15:13:35 and read 12355 times.

Quoting Starlionblue (Reply 91):
Yes rain makes air more dense.

...but not directly : in terms of aerodynamics, the important pârameter is rhô, the **density** of the air molecule.
That density is, among other things dependent on the watervapour content of said molecule.
Present water would just push the vapôur content to the saturation point for the conditions one encounters : temperature in particular and pressure.

Quoting Wisdom (Reply 92):
ft typically increases but drag increases faster. Hence L/D ration decreases.

All the studies NASA lead in this field disprove that statement :
;;;all configurations - cruise / landing with slats and flaps down - experienced significant losses in maximum lift capability, increase in drag for a given lift condition and a progressive decrease in the lift curve slope as the water content increased...
The NACA 64-210 data indicfdated that the severity of the rain effect appears to be configuration-dependent and is most severe for high lift configurations airfoils with leading edge and trailing edge devices configured for landing or takeoff operations...
...analyses indicated that a B747 encountering a rain cloud with a water content of 18 g/m3 would experience a 5% increase in drag, a 29% reduction in maximum lift capability and a 5% reduction in the AoA for maximum lift..."

Ref :
Wind Tunnel Aerodynamic Characteristics of a
Transport-Type Airfoil in a Simulated Heavy Rain Environment.Nasa


Quoting Wisdom (Reply 92):
The study provided is inadequate in the sense that if you want to prove something you can prove it.
They were similating a given airfoil at a given airspeed (less than 100km/h by the way), and given water flow, which provided given results.
Quoting Wisdom (Reply 92):
Unless they did it with a B738 wing at the approach speeds and the same precipitation rate+volume, the study isn't adequate to prove anything but a possible outcome.
Quoting Wisdom (Reply 92):
At the typical approach speed of 140kts, or twice the speed than in the experiment,

You apparently forgot that for wind tunnel testing, engineers introduce an effect of scale and a set of Reynolds numbers in order to simulate actual conditions on the full scale wing.
Your above statements are totally incorrect.

Quoting Wisdom (Reply 92):
the boundary layer won't let many droplets come into contact with the airfoil. Instead, they will come to increase the density of the boundary layer and energise it, increasing lift.

1: I have never seen a dry wing in rain.
2: sheet layer of water in the fore part of the wing modifies the profile in a detrimental way.
3: the formation of water rivulets past the laminar flow ( the sheet layer ) affects the lift further.
4: the result is an important decrease of the lift coefficient.

Quoting Wisdom (Reply 92):
On the other hand, thrust available will increase

See PW100 posts above. Your statement is patently untrue.

Quoting liquidair (Reply 99):
I had no idea about the 707!

That solution was, as a matter of fact, quite wide-spread on early turbojets / turbofans.
Civil airliners so equipped were all the aircraft equipped with the PW JT-3, JT-9s, so they include 707, DC-8, B747-100... the most notorious user was the B-52.
Water injection (with some alcohol added ) in the engine intake venturi would cool the ingested air, therefore augmenting its **density**. That will trick the engine into thinking it was operating in a denser atmosphere, thus increasing thrust... that was the main use of water injection. I used to fly the latest of AF 741 cargo planes so equipped : 2000 l of water for the two or so minutes of use : 200 liters / min on each engine or a bit more than 3 l / sec. Really not a lot... but a lot of unburned fuel and emission of a thick black smoke at exhaust... Not very ecological.
With modern ECU and FADEC, the electronics will take charge and correct that sort of conditions.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: liquidair
Posted 2013-04-17 16:22:43 and read 12153 times.

Quoting rcair1 (Reply 101):

sounds interesting...maybe an idle engine setting precipitated things? I can't remember which post, but I'm sure someone mentioned the captain saying he selected toga and nothing happened.

Quoting Pihero (Reply 103):

I guess it's a bit like the aquamist system on my car- spraying ethanol/water mixture on the intercooler. Probably a bit bigger though... Mine only holds 5 litres!

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: LTC8K6
Posted 2013-04-17 17:33:48 and read 12037 times.

http://www.youtube.com/watch?v=faDWFwDy8-U

There is a water ingestion test, just to give an idea.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: airtechy
Posted 2013-04-17 18:57:55 and read 11936 times.

Some pics of the aircraft removal here.....

http://photoblog.nbcnews.com/

....you may have to scroll down.

Looks like they pulled the seats.....maybe to reduce weight.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-17 21:44:14 and read 11665 times.

I see the painters have been busy.


Quoting airtechy (Reply 105):
Looks like they pulled the seats.....maybe to reduce weight.

I think it is more likely that they took the seats out because most of them were fine and could be reused.

[Edited 2013-04-17 21:44:46]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-18 02:04:36 and read 11194 times.

Quoting Wisdom (Reply 107):
How do you dare to criticize without knowing the other party's knowledge level and background?

As I mentioned before, all other posters have shown remarkable restraint despite you constantly being condescending and rude to them. They've criticized your statements, not your person. You, on the other hand, insist on acting like a total pillock despite being repeatedly and patiently asked not to do so. And now you get on your high horse, saying how smart you are and how other people don't have the requisite background. Classy...


You're being so condescending and insulting that I won't even address your other points. I'll just suggest deletion.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-18 02:19:26 and read 11177 times.

For those who disregard wind tunnel techniques and scaling aerodynamic conditions vs scale models, I just have one question :

How do you think aerodynamicists, working hand in hand with aircraft designers and engineers manage to forecast with a high degree of precision the performance and the behaviour of their design with 1/20 th - max - scale mock-ups ?
All the aircraft around started with wind tunnel experiments. All of them.
... and don't tell us about tri-dimensional computer aerodynamic solutions as they are still not accurate enough to displace needed wind tunnel data.

Flight testing is in many ways validation of these wind tunnel results... and yes, there could be some discrepancies but in the order of 1%... remember the " we are actually 1 or 2 points better than initially anticipated in the wing performance... that translates into 200 more miles to our max range " for the 787 ?
The same applies with these NASA experiments : the initial studies lead in the eighties into the " add 10 kt to your approach speed in case of heavy rain" and, as a matter of fact the inclusion of that technique in modern FTMs.

The study is not about the 738, but a supercritical airfoil representative of modern airliners.

For all I care, feel free to disregard the results... at your peril - and unfortunately your passenger's too - of course.

As for me, I'll take this experimental study and its conclusions with a lot more respect than I would a self-appointed specialist writing in the protection of anonymity in this forum.

[Edited 2013-04-18 02:24:30]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: travelavnut
Posted 2013-04-18 02:19:56 and read 11202 times.

Quoting Wisdom (Reply 107):
I don't want to humiliate you, you're humiliating yourself with this pseudo-knowledge.

        

Pihero is one of the most respected members on this board, I suggest some humility on your part.

Quoting airtechy (Reply 105):
Some pics of the aircraft removal here.....

http://photoblog.nbcnews.com/

....you may have to scroll down.

This is a direct link; http://photoblog.nbcnews.com/_news/2...plane-lifted-from-sea-in-bali?lite

It looks like they cut the fuselage in 3 pieces, or was it already cracked this way without being visible?!

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-18 02:23:08 and read 11154 times.

Quoting travelavnut (Reply 110):
It looks like they cut the fuselage in 3 pieces, or was it already cracked this way without being visible?!

I suspect it was so cracked that it was simpler to keep cutting instead of lifting and having it bend when they lifted it and/or a weight/size limit for the crane.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: travelavnut
Posted 2013-04-18 02:27:44 and read 11171 times.

Quoting Starlionblue (Reply 111):
I suspect it was so cracked that it was simpler to keep cutting instead of lifting and having it bend when they lifted it and/or a weight/size limit for the crane.

It actually looks like they cut the fuselage in 4 pieces; the first photo shows the fuselage front of the wings being lifted, the cockpit is missing, so I guess they cut that off.... The pictures on AvHerald ( http://avherald.com/h?article=460aeabb&opt=0 ) only show a crack behind the wings.

That looks like quite a bit of cutting in knee deep water...

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-18 03:51:35 and read 11064 times.

Perhaps they figured they could salvage parts of the cockpit equipment and there was less risk of it falling in the water if they lifted it separately.

Quoting travelavnut (Reply 112):
That looks like quite a bit of cutting in knee deep water...

At least it's warm.  

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-18 04:12:08 and read 11024 times.

But they're destroying that lovely coral reef !      

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: btblue
Posted 2013-04-18 04:20:38 and read 11024 times.

Interesting link:

http://www.ntsb.gov/doclib/recletters/2005/a05_19_20.pdf

Talks about a TACA 737 with engines at flight idle while descending through 'heavy rain, hail and turbulence'.

I remember way back when I was a kid an Air Europe 737 that had dual flame-out while descending through a thunder storm over Greece. This is also mentioned in the above report.

Lots of similarities between these and the Lion Air accident.

[Edited 2013-04-18 04:22:29]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-18 04:31:41 and read 10996 times.

It's a possibility that I also considered in the first thread.

Quoting wisdom (Reply 147):
Reports of very heavy rain, so that could have caused a flame-out and inability to restart in time.

The Reuters report does not mention this. I would expect that it would have been mentioned if it was the case.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-18 05:07:54 and read 10883 times.

Quoting btblue (Reply 117):
Talks about a TACA 737 with engines at flight idle while descending through 'heavy rain, hail and turbulence'.

Yes there are quite a lot of similarities.
However, being on a 2.8 to 3° glide path with gear and full flaps would require a lot of thrust. They weren't at idle, or if they were, it was for a short time in order to correct a too-high situation - which doesn't show on the ADS-B read outs.

Gerry and other commentators on other sites seem to be proving the presence of rain with the fact that the windscreen wipers were not in their stowed position. I tend to agree as the thing is so obnoxious that we only use it - along with the rain repellent - in significant downpours.

Mandala499 also mentions that the flaps were full down. That suggests that the **go around** they attempted was in fact the *Windshear escape procedure*, in which we don't change the aircraft configuration - bar the speedbrakes - until we're out of the windshear.

There is also an intriguing titbit : the French passenger, Mr Grandy, in a later interview mentions the severe rainfall and a possible flameout of the right engine for which "the airplane turned". Neither pilot mentioned it.
So, I'll file it under "Witness report, reliability unknown"

For the time being, I stick to the facts at hand, of which there isn't a lot, really.

[Edited 2013-04-18 05:12:36]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: rfields5421
Posted 2013-04-18 05:09:16 and read 10851 times.

Quoting travelavnut (Reply 112):
That looks like quite a bit of cutting in knee deep water...

Don't forget the tides are changing water depth. For April 18 - there is a little over 1.1 M tidal change in water depth with high tides at near 1400 and 0300 today. The higher tide being in the day time.

Tides have been falling since the accident occurred, but will begin rising higher to a near 2.9 M change on the 28th.

On the 13th, the day of the accident - the tide fell 2.37 M from 1200 to 1800 local time - the crash happened about halfway through that falling tide.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: UALWN
Posted 2013-04-18 08:56:52 and read 10438 times.

Quoting Wisdom (Reply 120):

Hey, what happened to your promise to leave this thread that you made a couple of days ago? Please, do yourself and all of us a favor and keep to that promise.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: TheRedBaron
Posted 2013-04-18 09:06:41 and read 10405 times.

Looking for the cockpit in Ebay in 4 3 2 1.... I would be uber cool to have a complete nose with cockpit at home.... ah the posibilities with a FS... lol.

Pihero, WHAT if they lost power and they were pressing a go around and changing the procedures and they pulled and were dragged down and lost the posibility of a Go around? I mean they had mere seconds so its a posibility that both engines flamed out (even in a high power setting) or were severely compromised on power...so its another nail in the coffin so to speak....

Gled if you gave me your input on that...

TRB *surfing Ebay..

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-18 09:43:56 and read 10314 times.

Quoting TheRedBaron (Reply 121):
WHAT if they lost power and they were pressing a go around and changing the procedures and they pulled and were dragged down and lost the posibility of a Go around? I mean they had mere seconds so its a posibility that both engines flamed out (even in a high power setting) or were severely compromised on power...so its another nail in the coffin so to speak....

An intriguing theory...
However, I would think that the impact would have been a lot more severe, with many more casualties. No one reported a big shock, just a realisation that they were in the water.
That's the reason I believe that both engines were running and the go around initiation lessened the vertical component of the impact.

Because this incident has had so much adverse publicity for Indonesian air travel, I think that a preliminary report will come out quickly in order to quell the comments on how unsafe the airline and the crews are.

We shouldn't have long to wait.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: TheRedBaron
Posted 2013-04-18 10:04:19 and read 10228 times.

Thanks, I plan to fly over there in a few months and see or friend Superfly. I guess as most accidents this one is a long string of events that led to the water ... great there are no casualties...

TRB

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: neutrino
Posted 2013-04-18 10:14:52 and read 10211 times.

Quoting UALWN (Reply 120):
Hey, what happened to your promise to leave this thread that you made a couple of days ago? Please, do yourself and all of us a favor and keep to that promise.

It looks like he didn't have the wisdom    to do so.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: mandala499
Posted 2013-04-18 11:28:06 and read 10129 times.

Quoting Pihero (Reply 122):
Because this incident has had so much adverse publicity for Indonesian air travel, I think that a preliminary report will come out quickly in order to quell the comments on how unsafe the airline and the crews are.

The NTSC did their fastest final report on the Sukhoi accident last year... a mere 6 months after the accident. World record?

Quoting TheRedBaron (Reply 121):
I mean they had mere seconds so its a posibility that both engines flamed out (even in a high power setting) or were severely compromised on power...so its another nail in the coffin so to speak....

If such a rain was enough to flame a 738 out of both engines... then i suspect the Virgin jet behind it would suffer the same fate. The TACA 737 and both Garuda 737 that suffered flameouts (the latter was about 10 yrs ago and ended up landing in the river), were both at idle power. It's standard practice here to put the burncan igniters when descending on idle, and also on approaches in rain (IGN to BOTH)... even in the days before those two accidents...

One thing to note is that the landing weight of this aircraft is bound to be on the low end, so lower approach speed and lower power than the more usual weights... but whether that led to flameout or not, we don't know yet.

If both engines flamed out on short final, it would have been messier...
A single engine flameout is a non event.
A single engine flameout and a windshear... well... that would be interesting.

Unfortunately, it could have been as simple as a slow reaction to windshear by the crew...even the 'soft windshear' here have resulted in near misses with the fence in the past due to slow reaction...

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: travelavnut
Posted 2013-04-18 11:34:14 and read 10072 times.

Quoting mandala499 (Reply 125):
Unfortunately, it could have been as simple as a slow reaction to windshear by the crew...even the 'soft windshear' here have resulted in near misses with the fence in the past due to slow reaction...

I seem to remember reading the Captain took control when the PF lost sight of the runway (can't find the source unfortunately, but I think it was in multiple news articles, so pinch of salt is advised). Could this be a possible reason?

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-18 16:33:28 and read 9716 times.

Quoting travelavnut (Reply 124):
I seem to remember reading the Captain took control when the PF lost sight of the runway (can't find the source unfortunately, but I think it was in multiple news articles, so pinch of salt is advised). Could this be a possible reason?

It could contribute to confusion and delays. Then again it could also be a good thing. Whether to take over or not depends on company SOP and also on the individual captain's decision. Certainly there should be a well defined procedure.

In the "Mayday" episode with the BA 777 crash at LHR, the captain said he considered taking over but since the F/O had the situation in hand he did not. On the other hand Captain Sullenberger took over immediately. I think you can't say for sure whether it is a good or bad thing to take over. It depends on the situation and the crew.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: frmrcapcadet
Posted 2013-04-18 16:52:02 and read 9701 times.

"All the aircraft around started with wind tunnel experiments. All of them."

And if I remember correctly from my visit to the Smithsonian several years ago the Wright brothers suspected lift tables on airfoils were wrong, so built a wind tunnel and redid the tables.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-19 02:38:24 and read 9507 times.

Quoting frmrcapcadet (Reply 126):

"All the aircraft around started with wind tunnel experiments. All of them."

And if I remember correctly from my visit to the Smithsonian several years ago the Wright brothers suspected lift tables on airfoils were wrong, so built a wind tunnel and redid the tables.

Yes, those were the pioneer days !!! but considering the speeds achieved then, those gave pretty accurate predictions.
Nowadays, with the dimensions and the speed ranges the engineers have to consider, and taking into account that simulation is achieved when the Reynolds numbers of the scale model and those of the actual aircraft are the same,

In a first approximation, the wind tunnel needs to operate with higher pressure and lower temperature, with different gases for different viscosities.

This is a very interesting movie made by the *European Transsonic Windtunnel*. It shows, contrarily to an earlier uninformed quick comment that the accuracy of these experimentations is very high:

See this
ETW movie

Enjoy.

[Edited 2013-04-19 02:39:19]

[Edited 2013-04-19 02:40:48]

[Edited 2013-04-19 02:41:32]

[Edited 2013-04-19 02:46:21]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-19 03:53:53 and read 9384 times.

Like I said, this does not deliver anything close to representative of aerodynamic modelling.
The only way you can exploit it, is through comparison with other models, by introducing small tweaks.

Several of the issues:
-the strut holding the model in its position inserts a major error
-no engines running, which results in inaccurate airflow patterns around the wing
-no windows on the model
-polished surfaces, not representative of actual operating conditions, ie paint, gaps, antenna's, etc...
-the airframe is tested as a whole, the airfoil's lifting efficiency is thus approximated through analysis


So yes, it's accurate for a comparison between models and a wil approximation, but it's not accurate in the actual calculation of performance. This, I remind you is what you are implying.

Wind tunnels have been used from the very beginning, not to achieve accurate prediction of performance, but to gain knowledge on what positively affects aerodynamic performance and what negatively affects performance.
This is how you improve aerodynamics through wind tunnels.

It's not like you put the model in the wind tunnel and it's going to give you the picture perfect accurate modelling of aerodynamic performance applicable to all surfaces.      

Have you ever operated even the most basic of wind tunnels for aerodynamic testing? Because I have and like I said, the only thing you can do is to compare, tweak, compare, tweak, compare.

I'm currently developing a new generation wind turbine that looks nothing like the current designs. I base my calculation on formula's applicable to aerodynamics, then use comparative modelling to confirm what parameters affect the performance.
But it's much easier because wind turbines are fixed on the ground, unlike aircraft that fly loosely in the air.

If you want to predict performance accurately, you need a remote controlled perfectly replicated model jacked with sensors that is flying free in the air inside the wind tunnel. But the creation of each model would be so expensive that you won't be able to improve much by comparative analysis without spending a lot of money.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: zeke
Posted 2013-04-19 04:52:00 and read 9287 times.

Quoting Wisdom (Reply 128):

I disagree with a lot of what you are saying. Wind tunnel experiments do produce representative and very realistic data for the experiments they are designed for. Engineers design specific wind tunnel experiments to gain specific data, data sources such as NACA, NASA, ESDU, and DATCOM have numerous examples where theoretical computational results, wind tunnel experimental results, and flight test data are compared, in subsonic, transonic, and even supersonic flight.

Like all experiments, wind tunnel experiments are carefully designed to be representative, dimensional analysis is used extensively for this to get the correct scale. A poorly designed experiment will produce poor results, a carefully design experiment, with calibrated equipment will produce valid data.

The point of this testing is not to gain 100% accuracy for one set of conditions, it is to see how the model behaves as geometry/speed etc are varied, as that is how an aircraft will be operated.

Manufacturers are able to establish performance of new aircraft based upon wind tunnel and computational results to a very high accuracy, flight testing is then done to validate this data, and improve performance even more.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-19 05:39:42 and read 9165 times.

Quoting zeke (Reply 129):
Manufacturers are able to establish performance of new aircraft based upon wind tunnel and computational results to a very high accuracy, flight testing is then done to validate this data, and improve performance even more.

NASA lays it down better:


The results from computation are so accurate that some scientists and engineers doing airplane design believe that computation should completely replace wind tunnel research. Afterall, it's a lot easier to test something on the computer than to build a model and then do several wind tunnel tests. Other scientists think that experimental research, such as wind tunnel testing, and computational research are both needed. Many times the results from a wind tunnel test are compared to the results predicted by the computer. If one set of values is very different from the other set, then we know that something is wrong. By using both of these tools correctly engineers and scientists can insure that a design is ready to move on to the next steps: flight simulation and research flights.


About windtunnels:

It's there that scientists, engineers, and technicians can begin to understand how the airplane is performing.
From these different kinds of measurements, a great deal can be learned about the model being tested.

http://quest.arc.nasa.gov/aero/background/tools/


Like I said, you are saying and NASA is saying, wind tunnels are used for confirmation, not to determine the actual performance of an airfoil/airframe as Pihero is implying. In Pihero's experiment report, wind tunnel testing was used to determine loss of performance related to rain in a set of well-defined circumstances, to reach a well-determined conclusion valid for the experiment only. Pihero then conveniently generalised it into the B738 wing and this Lion Air accident scenario, implying that performance analysis from wind tunnel testing provides accurate data for ALL airfoils.
The goal of said experiment was not to prove that, it was to prove that rain CAN and WILL affect aircraft performance. I don't dispute that.

But to take the 28% figure and to copy-paste it here is not something rational to do, as it means nothing. If the B738 could lose 28% of lift to drag performance in rain, I'm sure that aircraft manufacturers would have landing performance tables that would include margins for precipitation.


When you develop a computer model or a paper model like I do, which is basically the same only that the math is done manually (which also allows easier tweaking by the way), wind tunnel testing serves only to compare, confirm and sometimes introduce tweaks to improve your design. Often, you just take the model and tweak it a little bit manually to see if the numbers improve, and afterwards try to calculate why this improves. Once you figure it out, you can see if the rest of the design can't be improved even more using the same rational.

Conclusion: A wind tunnel is not a means to determine absolute performance of an aircraft/airfoil with all the possible variables, it's a means of validating and improving designs based on COMPARATIVE ANALYSIS.

[Edited 2013-04-19 05:44:22]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: bikerthai
Posted 2013-04-19 06:51:27 and read 9045 times.

Quoting Starlionblue (Reply 106):
I think it is more likely that they took the seats out because most of them were fine and could be reused.

Yes seats seems like one of those commodities that gets swap out often enough that extra seats are good to have.
Besides, those seats are so easy to remove that it just make sense to remove them whether they are salvagable or not.

Note that they removed a bunch of windows and window panes besides the ones that they used to wrap the straps through . . . another commondity that is good to have?

bt

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-19 07:19:50 and read 9016 times.

Quoting zeke (Reply 129):
Wind tunnel experiments do produce representative and very realistic data for the experiments they are designed for. Engineers design specific wind tunnel experiments to gain specific data, data sources such as NACA, NASA, ESDU, and DATCOM have numerous examples where theoretical computational results, wind tunnel experimental results, and flight test data are compared, in subsonic, transonic, and even supersonic flight.

  

Quoting zeke (Reply 129):

Manufacturers are able to establish performance of new aircraft based upon wind tunnel and computational results to a very high accuracy, flight testing is then done to validate this data, and improve performance even more.

     
How come you write better English than I do ?   

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Starlionblue
Posted 2013-04-19 07:25:22 and read 8999 times.

Quoting Pihero (Reply 132):
Quoting zeke (Reply 129):

Manufacturers are able to establish performance of new aircraft based upon wind tunnel and computational results to a very high accuracy, flight testing is then done to validate this data, and improve performance even more.

     
How come you write better English than I do ?

Hong Kong. We're not part of The Empire anymore but the heritage prevails. 
Quoting bikerthai (Reply 131):
Quoting Starlionblue (Reply 106):
I think it is more likely that they took the seats out because most of them were fine and could be reused.

Yes seats seems like one of those commodities that gets swap out often enough that extra seats are good to have.
Besides, those seats are so easy to remove that it just make sense to remove them whether they are salvagable or not.

Note that they removed a bunch of windows and window panes besides the ones that they used to wrap the straps through . . . another commondity that is good to have?

Definitely. Cheap and easy to remove but costly parts.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-19 08:16:05 and read 8875 times.

Quoting bikerthai (Reply 131):
Quoting Starlionblue (Reply 106):
I think it is more likely that they took the seats out because most of them were fine and could be reused.

Yes seats seems like one of those commodities that gets swap out often enough that extra seats are good to have.
Besides, those seats are so easy to remove that it just make sense to remove them whether they are salvagable or not.

Note that they removed a bunch of windows and window panes besides the ones that they used to wrap the straps through . . . another commondity that is good to have?

bt

I don't know how it's done in Indonesia but seats that have been in a crash with high G are normally considered scrap due to the forces that they were subjected to. If a return to service would be considered, they would have to be subjected to NDT and detailed visual inspection to see if there aren't any cracks inside.
The huge cost of NDT wouldn't make it worthwhile in Europe, but this is Indonesia and I guess that they would just do a on-paper certification after inspecting one or two chairs.

The cushions and covers could however be salvageable.

If you ask me, the manpower, logistics and storage cost wouldn't be worth it. The economy class chairs themselves rarely require any replacement. All that can go wrong with them is the reclining, armrests and tray tables and all these parts are available as spares.

If they salvage the chairs, they might as well take a look in the E&E bay... A lot more valuable stuff in there.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: gatorman96
Posted 2013-04-19 08:45:12 and read 8786 times.

Quoting Wisdom (Reply 134):
If they salvage the chairs, they might as well take a look in the E&E bay... A lot more valuable stuff in there.

Yeah, an EE bay and saltwater go great together...

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-19 09:50:18 and read 8650 times.

Quoting gatorman96 (Reply 136):

Quoting Wisdom (Reply 134):
If they salvage the chairs, they might as well take a look in the E&E bay... A lot more valuable stuff in there.

Yeah, an EE bay and saltwater go great together...

Do they? I didn't know that. (Irony³)

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: airmagnac
Posted 2013-04-19 10:55:01 and read 8521 times.

Quoting Pihero (Reply 127):
Yes, those were the pioneer days !!! but considering the speeds achieved then, those gave pretty accurate predictions.

Ironically, the relatively small Reynolds numbers seen in basic wind tunnels led early airplane designers down a wrong path. With small Reynolds, there will often be a "bubble" forming over the airfoil that will eventually burst with very negative consequences on the flow. This phenomenon increases with thickness...so basically thin airfoils behave better at low Reynolds numbers. But at higher real-world Reynolds it's the opposite ! because in this case flow will more easily seperate from the sharper leading edge of the thin airfoils.
So, based on wind tunnel tests, most early wing designs used extremely thin airfoils (cloth stretched over a wooden frame), even though the real performances of these wings was lower than the real performances of thick wings ! Check out all those Voisin, Bleriot, Farman, Morane, De Havilland, Wright or WW1 aircraft.
I think it's only in 1917 that Prandtl and his team in Göttingen figured out the problem, and contributed to produce the thick-winged Fokker Triplane. And then NACA (with Max Munk, coming from Göttingen) built the variable density tunnel in the 1920s, to adapt the Reynolds number.

But I digress...  

[Edited 2013-04-19 11:05:22]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: bikerthai
Posted 2013-04-19 11:48:24 and read 8434 times.

Quoting Wisdom (Reply 134):
I don't know how it's done in Indonesia but seats that have been in a crash with high G are normally considered scrap due to the forces that they were subjected to.

Yes, except this was not a high G crash. Most 16 G seats have frangible mechanism that can easily be detected when the 16 G foward load condition have been applied. For static load requirement, static proof testing of a small sample set can be done with the assumption that the seats in same section of the airplane would see the same loading.

Whiffle tree testing of the seat is pretty straight forward and the OEM probably has facilities that can do this at reasonable price.

You are right about the cost of inspection of every seat though. They don't have to send it to Europe, China would be adequate 
Quoting Wisdom (Reply 134):
The cushions and covers could however be salvageable.

They'll have to try to get the salt air smell out of it first. Cushions and covers are even cheaper to replace.

Did the airplane have seat back entertaiment system? That may be salvagable as they are designed to resist spilled coffee and are not a flight safety item. . . not from a structures point anyway.

bt

[Edited 2013-04-19 11:49:14]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: scbriml
Posted 2013-04-19 12:47:47 and read 8355 times.

Quoting bikerthai (Reply 141):
Did the airplane have seat back entertaiment system?

This is Lion, you know.   

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-19 13:46:02 and read 8254 times.

Quoting bikerthai (Reply 141):
Did the airplane have seat back entertaiment system? That may be salvagable as they are designed to resist spilled coffee and are not a flight safety item. . . not from a structures point anyway.

Where I used to work, they were considered avionics. Avionics that have been in contact with water are scrap.

Quoting bikerthai (Reply 141):
Yes, except this was not a high G crash. Most 16 G seats have frangible mechanism that can easily be detected when the 16 G foward load condition have been applied. For static load requirement, static proof testing of a small sample set can be done with the assumption that the seats in same section of the airplane would see the same loading.

I've thought of that. The question is whether they kept all seats in the same order.  
My definition of high G is anything above 5G. If 3 big guys were seated in the same row, this would equate to 1500kg resting of compression load on those thin aluminium legs.

Are the logistics of moving and storing all those seats even worth the effort of 1 or 2 seat rows that they may ever have to replace? If they were in contact with salt water, they would have to be pressure-washed and dried very fast or else they would start to corrode.
I would think that overhead bins would be much more interesting as they're quite expensive and also see more abuse, and often have determined positions in the cabin (while seats are mostly the same, except for first and last rows). Except for the closing mechanism and the fixtures, they're all plastic, and given their position high up, they may not have seen as much salt water.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: zeke
Posted 2013-04-19 23:25:43 and read 7968 times.

Quoting Wisdom (Reply 130):

I do not believe that waffle, wind tunnel testing is still used today. Computational results are good, however they have their limits, and that is with the mesh and assumptions used in the model. We still cannot calculate everything going on in a cup of coffee if we add some milk and stir it, and that is a "simple" everyday experiment I do that a computer cannot.

Quoting bikerthai (Reply 141):

As with any aviation insurance claim, all parts removed are the property of the insurer, and the aircraft and its contents are also theirs. I have never heard of an insurer selling parts from an aircraft that they have written off like this. The liability aspects I think for them are just not worth it.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: mandala499
Posted 2013-04-20 08:10:25 and read 7689 times.

OK... just got info...
Windshear was at 200ft, and despite the captain having known to be a "slowmo dude" (but within the lag reaction parameters required) in training in the past, this case seems the FO was the PF. Late reaction to go around still suspected.

Was not a hard slam windshear or a soft shear, but progressed from one to the other quickly. Am hearing info that the windshear alert failed to scream.

TOGA was pressed but throttle was on manual... no further info on this yet on whether full G/A thrust was applied... it is likely that by the first water impact, engines had not yet spooled up to TOGA thrust...

To be honest, this botched G/A with suspected late G/A thrust application by some twist of fate is better than a slightly earlier spool up... putting the aircraft on the sea wall and creating a big mess and undoubtedly, loss of life.

One of those days I guess  

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: AirlineCritic
Posted 2013-04-20 09:49:46 and read 7528 times.

Quoting mandala499 (Reply 142):
Windshear was at 200ft, and despite the captain having known to be a "slowmo dude" (but within the lag reaction parameters required) in training in the past, this case seems the FO was the PF. Late reaction to go around still suspected.

Was not a hard slam windshear or a soft shear, but progressed from one to the other quickly. Am hearing info that the windshear alert failed to scream.

TOGA was pressed but throttle was on manual... no further info on this yet on whether full G/A thrust was applied... it is likely that by the first water impact, engines had not yet spooled up to TOGA thrust...

Very interesting, thanks for the info!

Quoting mandala499 (Reply 142):

To be honest, this botched G/A with suspected late G/A thrust application by some twist of fate is better than a slightly earlier spool up... putting the aircraft on the sea wall and creating a big mess and undoubtedly, loss of life.

Indeed. If the above information turns out to be true, this seems to apply as well:

Quoting mandala499 (Reply 142):

When losing situational awareness, pray Cumulus Granitus isn't nearby !

  

What an amazing accident. The windshear, spool up time, and pilot error holes in the cheese were aligned. But fortunately, the sea wall hole was not aligned, so it turned out survivable for everyone. Good outcome... for everyone, except the insurers, but who cares about them 

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: n471wn
Posted 2013-04-20 10:09:15 and read 7474 times.

Is the a/c out of the water yet?

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Wisdom
Posted 2013-04-20 12:55:27 and read 7375 times.

Quoting mandala499 (Reply 142):
OK... just got info...
Windshear was at 200ft, and despite the captain having known to be a "slowmo dude" (but within the lag reaction parameters required) in training in the past, this case seems the FO was the PF. Late reaction to go around still suspected.

Was not a hard slam windshear or a soft shear, but progressed from one to the other quickly. Am hearing info that the windshear alert failed to scream.

TOGA was pressed but throttle was on manual... no further info on this yet on whether full G/A thrust was applied... it is likely that by the first water impact, engines had not yet spooled up to TOGA thrust...

To be honest, this botched G/A with suspected late G/A thrust application by some twist of fate is better than a slightly earlier spool up... putting the aircraft on the sea wall and creating a big mess and undoubtedly, loss of life.

One of those days I guess  

If the EGPWS didn't scream, it either means that
-there was a problem with the EGPWS,
-that it wasn't windshear or
-that it was very light windshear and the crew failed big time.

It's atypical of microburst that you would have heavy rain from 400ft to 200ft and only then suddenly a downdraft, so if this was windshear, it must have been a very mild one and not attributed to a microburst event. So certainly not sufficient to crash the B738 if the correct procedures were followed.

I'm pretty sure that when you press TOGA on all Boeing aircraft, regardless of your mode, it will activate the G/A mode of your A/T. Many airlines make TOGA standard regardless of A/T on or off, because it allows you to focus on the actual threat (in fact, TOGA could have saved the TK B738 in AMS) and makes the go-around final even if crew members disagree in the worst CRM scenario.

The more we know, the more questions it raises.

[Edited 2013-04-20 12:56:44]

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: zeke
Posted 2013-04-21 01:44:05 and read 7012 times.

Quoting Wisdom (Reply 145):
It's atypical of microburst that you would have heavy rain from 400ft to 200ft and only then suddenly a downdraft, so if this was windshear, it must have been a very mild one and not attributed to a microburst event. So certainly not sufficient to crash the B738 if the correct procedures were followed.

You mean you are somehow surprised that nature is not "typical" ?????

Quoting Wisdom (Reply 145):
I'm pretty sure that when you press TOGA on all Boeing aircraft, regardless of your mode, it will activate the G/A mode of your A/T. Many airlines make TOGA standard regardless of A/T on or off, because it allows you to focus on the actual threat (in fact, TOGA could have saved the TK B738 in AMS) and makes the go-around final even if crew members disagree in the worst CRM scenario.

And I am pretty sure pressing the TOGA on the 737NG activates the G/A F/D mode, it dose nothing to thrust when manually flown.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-21 01:59:15 and read 6996 times.

Quoting mandala499 (Reply 142):
Windshear was at 200ft, and despite the captain having known to be a "slowmo dude" (but within the lag reaction parameters required) in training in the past, this case seems the FO was the PF.

I am surprised there's no mention of the triggering factor in this accident : Heavy rain reported by the occupants of the airplane, crew and passengers alike.
To concentrate only on the windshear aspect is probably not enough to explain the chain of events.

Quoting mandala499 (Reply 142):
Was not a hard slam windshear or a soft shear, but progressed from one to the other quickly. Am hearing info that the windshear alert failed to scream.

As at low altitudes, we augment the radar tilt, it's quite possible that it could miss the shear at the airplane's level : the beam is higher and could miss the horizontal windshift.

Quoting mandala499 (Reply 142):
this case seems the FO was the PF

I thought captain took over control during the heavy rain that blinded outside view... and the runway.

Quoting mandala499 (Reply 142):
TOGA was pressed but throttle was on manual... no further info on this yet on whether full G/A thrust was applied...

Doesn't an AT disconnect A/T leave it in the **Armed** mode : in this case, depressing the TOGA switches will give an automatic reduced TOGA thrust, levers advancing on their own and all ? and a second depress will give you full thrust ? along with FD guidance ?

Considering the above, I am not buying "pilot error" - yet :
- The initial cause was heavy rain - with a probable important downdraft - and some loss of lift.
- At two hundred feet - they were quickly below the approach descent path - then windshear hit and it was rather sudden...
- By taking over, the captain had already planned the possibility of a go around... that fact should lessen the case of a* botched manoeuvre*
- Time for analysis was ultra-short : what the pilot saw was lack of energy and no climb capability ; whatever the reasons were, it's just a matter of immediate perception, not logical understanding of all the factors involved.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: airmagnac
Posted 2013-04-21 02:39:18 and read 6902 times.

Quoting Wisdom (Reply 145):
If the EGPWS didn't scream, it either means that
-there was a problem with the EGPWS,
-that it wasn't windshear or
-that it was very light windshear and the crew failed big time.

The operating principle of any predictive warning system is to make measurements of the environment, compare those to known "signatures" of a given phenomenon, and if there is a correlation, then send out a warning.
But even if it is working properly, any such system is only as good as the measurement inputs and the knowledge of the phenomenon.
The sensors could very well miss some clues if not calibrated or directed in the right direction (see the earlier discussion about rain detection for METARs ; also, see

Quoting Pihero (Reply 147):
As at low altitudes, we augment the radar tilt, it's quite possible that it could miss the shear at the airplane's level : the beam is higher and could miss the horizontal windshift.

If you don't sense the problem, you can't send a warning about it.

Second, if a phenomenon is not completly understood, then the signatures programmed in the system may not cover all possible cases. In which case the measurements will not correlate with anything, and no warning will be sent.


We are neither omniscient nor omnipotent, it is dangerous to reason in absolutes such as "a windshear event will always be detected". Especially if this will be used as a basis for a blame-game.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: Pihero
Posted 2013-04-21 03:15:52 and read 6841 times.

Quoting zeke (Reply 146):
And I am pretty sure pressing the TOGA on the 737NG activates the G/A F/D mode, it dose nothing to thrust when manually flown.

In this instance *sure* is in fact *correct*.
Sorry I forgot to mention that fact in my latter post.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: mandala499
Posted 2013-04-21 15:12:04 and read 6385 times.

Quoting Wisdom (Reply 145):
I'm pretty sure that when you press TOGA on all Boeing aircraft, regardless of your mode, it will activate the G/A mode of your A/T. Many airlines make TOGA standard regardless of A/T on or off, because it allows you to focus on the actual threat (in fact, TOGA could have saved the TK B738 in AMS) and makes the go-around final even if crew members disagree in the worst CRM scenario.

Sorry, I think Zeke and Pihero is correct. VORDME approaches at or near minima would be flown manual thrust in Lion Air. TOGA would only apply the G/A on the FD... as per:

Quoting zeke (Reply 146):
And I am pretty sure pressing the TOGA on the 737NG activates the G/A F/D mode, it dose nothing to thrust when manually flown.

Which was also reiterated by one NG pilot who dropped by my house yesterday.

Quoting Wisdom (Reply 145):
If the EGPWS didn't scream, it either means that
-there was a problem with the EGPWS,
-that it wasn't windshear or
-that it was very light windshear and the crew failed big time.

You need to fly over here in the rain then!    Lots of cases here where you get windshear without the airplane screaming it out... and nothing wrong with the EGPWS either.

Quoting Pihero (Reply 147):
I am surprised there's no mention of the triggering factor in this accident : Heavy rain reported by the occupants of the airplane, crew and passengers alike.
To concentrate only on the windshear aspect is probably not enough to explain the chain of events.

Spot cells of the Magenta kind... am sure U know what I mean... Which leads to:

Quoting Pihero (Reply 147):
As at low altitudes, we augment the radar tilt, it's quite possible that it could miss the shear at the airplane's level : the beam is higher and could miss the horizontal windshift.

And this is usually the cause of the windshear not detected by the EGPWS I guess.
Let's see how long before someone says doing that is totally wrong...   

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: cargolex
Posted 2013-04-22 07:31:47 and read 5913 times.

I've been following these two threads since they began, and after several hours in the original thread, I was shocked to realize that I had captured this aircraft in my lens a few weeks ago.

In happier times as 9M-LNB:


View Large View Medium
Click here for bigger photo!

Photo © A. Kwanten

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: deepunderground
Posted 2013-04-23 03:16:06 and read 5503 times.

A lot of people posting here are trying to envision Indonesian weather as similar to your home area. It's not. And if you think Bali is strange, you should come visit me in the Papuan highlands!

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: neutrino
Posted 2013-04-23 08:31:31 and read 5198 times.

Quoting deepunderground (Reply 152):

Right, and should anyone take up your invitation, bring them to experience the equatorial snowfields of Punjak Jaya.   

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: rfields5421
Posted 2013-04-23 08:55:40 and read 5142 times.

Quoting neutrino (Reply 153):
Punjak Jaya

Thank you.

I learned something new. One reason I enjoy these forums so much.

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: neutrino
Posted 2013-04-23 09:21:46 and read 5071 times.

Quoting rfields5421 (Reply 154):

My pleasure. Ditto yours truly.
WE, whose ears are readily open to others' mouths will always keep learning.  

Topic: RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2
Username: RickNRoll
Posted 2013-04-23 20:38:41 and read 4758 times.

Quoting deepunderground (Reply 152):
A lot of people posting here are trying to envision Indonesian weather as similar to your home area. It's not. And if you think Bali is strange, you should come visit me in the Papuan highlands!

An interesting read about air safety in New Guinea.

http://www.abc.net.au/foreign/content/oldcontent/s2464246.htm

Basically, investigations don't even happen, and it's one of the most dangerous places to fly in the world.


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