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Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 10:54 am

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
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Gonzalo
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 11:20 am

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


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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 12:09 pm

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....
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 12:48 pm

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]
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 1:40 pm

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.
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 1:51 pm

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?
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 2:09 pm

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.
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 2:12 pm

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.
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 2:20 pm

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.
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 2:37 pm

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 ?"

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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 3:23 pm

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.
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 4:10 pm

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]
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 4:18 pm

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?
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 4:33 pm

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.

  
 
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200 Feet MSL About 1nm Short Of The Touch Down Zon

Mon Apr 15, 2013 5:47 pm

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]
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 5:57 pm

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.
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 6:12 pm

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
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 6:24 pm

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.
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 6:26 pm

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..."
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 6:53 pm

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]
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 7:03 pm

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.
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 7:29 pm

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.
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 7:43 pm

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.
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 7:47 pm

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.
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 7:58 pm

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.
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 8:23 pm

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.
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 8:25 pm

In addition, I might add that on such an overall nice afternoon, none of us had our radar turned on.
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 8:30 pm

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.
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 8:54 pm

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
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 9:10 pm

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.

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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 9:26 pm

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.
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 9:51 pm

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.
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 10:14 pm

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?
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 10:14 pm

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.   
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 10:38 pm

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]
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 10:47 pm

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.
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 11:03 pm

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.
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Mon Apr 15, 2013 11:48 pm

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]
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Tue Apr 16, 2013 12:15 am

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]
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Tue Apr 16, 2013 12:33 am

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]
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Tue Apr 16, 2013 12:50 am

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.
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Tue Apr 16, 2013 12:56 am

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]
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airtechy
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Tue Apr 16, 2013 12:58 am

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.
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Tue Apr 16, 2013 1:01 am

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]
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Tue Apr 16, 2013 1:40 am

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.
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Tue Apr 16, 2013 1:50 am

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).
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Tue Apr 16, 2013 2:12 am

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?
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Tue Apr 16, 2013 3:23 am

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.
 
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Tue Apr 16, 2013 3:31 am

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.  
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RE: Lion Air 738 Ditches In Sea Off DPS Runway Part 2

Tue Apr 16, 2013 3:56 am

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.