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B744 High Rate Of Descent  
User currently offlineSevenHeavy From United Kingdom, joined Mar 2004, 1156 posts, RR: 10
Posted (9 years 5 months 3 weeks 4 days 18 hours ago) and read 4721 times:

Hi,

I recently read a trip report on a B744 that detailed a descent from FL280 (ish)to landing in around 5 minutes. I have no desire to try to validate (or not) this claim but it did get me thinking and if anyone can provide any information on the following I would appreciate it:

1. This would equate to an average rate of descent of nearly 6000fpm. Assuming that initially the descent rate would be higher to allow for a stabalised approach is this remotely achievable under normal passenger (or any commercial) operations?.

2. Are there even any (non emergency) situations i.e. ATC clearances that would require this type of descent?.

3. what kind of workload would this put on the crew to get the aircraft in an acceptable configuration for a stabalised approach path?.

Lastly I have used the B744 as that was the aircraft involved but it is really a queation applicable to any large jet aircraft. I have heard for example that the A340 is particularly difficult to slow down and requires considerable planning and skill to effect a very quick controlled descent because of its "slippery" profile?

Thanks and regards,

SevenHeavy


So long 701, it was nice knowing you.
20 replies: All unread, jump to last
 
User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 1, posted (9 years 5 months 3 weeks 4 days 17 hours ago) and read 4595 times:

From FL280 to a landing in 5 minutes, is not too likely. I read the same report (flying over Antarctic from ORD-HKG).

It could be done by lowering the gear and you will fall out of the sky. However, you do need to get the flaps out and that does take some time. You can always configure at or below FL200 (Max flap extension FL200) and descend with flaps 20 and 180-200kias. However, the descent profile into HKG doesn't really need a descent like that.

HKG tends to keep you up a little high and they do cut some corners on the vectoring so if you are high it's tough to get down.

The workload imposed on the crew in a situation like as described could be very heavy. But, if the crew knew what was coming and was prepared, it might not be a real big deal.


User currently offlineMandala499 From Indonesia, joined Aug 2001, 6878 posts, RR: 75
Reply 2, posted (9 years 5 months 3 weeks 4 days 17 hours ago) and read 4574 times:

The steeper the descent, the faster you go too... How would the aircraft stabilize? Start to level off earlier than usual... think ahead and smoothly or the pax will start panicking or worse... throwing up. Plus/hence, you need more distance to stabilize.

Where I have heard this in a non emergency is an LH744 coming into Jakarta from Singapore. Leaving it's cruise level, it was told to contact arrivals... Arrivals then said something quite unusual. "LH### there are 5 traffic, if you want to be ahead I can give you heading 220, maximum speed and descent. Do you want to take it?"

LH took it... ATC then instructed "...heading 220 descend to 4000 at max speed and report reaching."

LH reported back... "heading 220 and down to 4000, will report reaching 4000. passing FL330 now... LH###"

Out of curiousity, I looked at the clock and it was 1723 local by my watch. Just before the 5 minutes was up... "LH### at 4000"...

After that he was to contact approach for final vectoring for 07L... I thought to myself.. that must be close to about 6000fpm descent... it is possible, but I have been told that it can be an uncomfortable descent doing it. (speedbrakes out?)

There are some rules of thumb that can come out of familiarity with the aircraft... like 5 miles to slow down from 300KIAS to 250KIAS on idle for 732 at about 47tons... or things like that...

Mandala499



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlineJAM747 From United States of America, joined Feb 2005, 550 posts, RR: 1
Reply 3, posted (9 years 5 months 3 weeks 4 days 15 hours ago) and read 4486 times:

Would'nt such a rapid descent put considerable stress on the aircraft? I have heard of aircrafts that need to descend fast to a specific location doing a spiral desent depending on airway traffic. Would such a descent make it less stessfull for a aircraft?

User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 4, posted (9 years 5 months 3 weeks 4 days 15 hours ago) and read 4485 times:

As long as no limits are exceeded there is no undue stress on the airframe.

Rule of thumb, for the -400 to slow from 300 to 250, plan on 10 miles at 200Tons, at 300 tons, it's 13miles.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17044 posts, RR: 67
Reply 5, posted (9 years 5 months 3 weeks 4 days 13 hours ago) and read 4448 times:

Quoting JAM747 (Reply 3):
Would'nt such a rapid descent put considerable stress on the aircraft? I have heard of aircrafts that need to descend fast to a specific location doing a spiral desent depending on airway traffic. Would such a descent make it less stessfull for a aircraft?

As PhilSquares points out, airliners are quite rugged. All the stress would be on the part of the pax Big grin



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineBRAVO7E7 From United States of America, joined Jul 2004, 1840 posts, RR: 17
Reply 6, posted (9 years 5 months 3 weeks 4 days 9 hours ago) and read 4375 times:

You don't have to believe me, but this is what happened. Keep in mind that we burned nearly four tons of fuel on the ground just waiting to take off. This flight has a flight time if over 15 hours, being United's longest flight. Since we almost had to land in Beijing due to lack of fuel, the aircraft was obviously getting pretty dry. Like I said, it felt almost like a free fall, and was extremely sharp.

User currently offlineMandala499 From Indonesia, joined Aug 2001, 6878 posts, RR: 75
Reply 7, posted (9 years 5 months 3 weeks 3 days 20 hours ago) and read 4206 times:

then there's the "leaf science" of the 737... flap40 gear down idle thrust, -4000fpm at 150 KIAS... just make sure U plan ahead, level off early and let the engines spool up otherwise you could see ship masts above the horizons  

Oh and don't forget the flap limit speed... U don't want them ripping off pulling out of a descent at low level and idle engines !

One or two airports here "require" such "manouvers" if a 744 goes there it would be quite a sight!

Mandala499

[Edited 2005-04-03 13:19:12]


When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlineBobbyBoeing From Germany, joined Mar 2005, 5 posts, RR: 0
Reply 8, posted (9 years 5 months 3 weeks 3 days 11 hours ago) and read 4120 times:

Hello all,

does anybody know, when this happened? I'm interested in the exact date!


User currently offlineNewark777 From United States of America, joined Dec 2004, 9348 posts, RR: 29
Reply 9, posted (9 years 5 months 3 weeks 3 days 11 hours ago) and read 4110 times:

Quoting BobbyBoeing (Reply 8):
does anybody know, when this happened? I'm interested in the exact date!

Here's the trip report, with all the dates and flight numbers.

Adventure On United(UA) From TPA-HKG (with Pics) (by BRAVO7E7 Apr 2 2005 in Trip Reports)

Harry



Why grab a Heine when you can grab a Busch?
User currently offlineRightWayUp From United Kingdom, joined Oct 2001, 86 posts, RR: 0
Reply 10, posted (9 years 5 months 3 weeks 3 days 11 hours ago) and read 4107 times:

And don't forget about the pressurisation, very uncomfortable!

User currently offlineMusapapaya From United Kingdom, joined Apr 2004, 1091 posts, RR: 0
Reply 11, posted (9 years 5 months 3 weeks 3 days ago) and read 4005 times:

Is that the ATC who gave this specific instruction for this UA plane to descend like this?
I bet this is rather abnormal...



Lufthansa Group of Airlines
User currently offlineWing From Turkey, joined Oct 2000, 1572 posts, RR: 24
Reply 12, posted (9 years 5 months 3 weeks 2 days 23 hours ago) and read 3991 times:

Airline airplanes can withstand such high rate of descents and passenger comfort can be traded with safety if needed but on a normal day operations I don't see a good reason to do that kind of rushed approaches.Anytime you rush inflight you increase your chances to forget something and create your self more troubles.


Widen your world
User currently offlineBRAVO7E7 From United States of America, joined Jul 2004, 1840 posts, RR: 17
Reply 13, posted (9 years 5 months 3 weeks 2 days 10 hours ago) and read 3872 times:

Quoting Musapapaya (Reply 11):
Is that the ATC who gave this specific instruction for this UA plane to descend like this?

Well, let me say that the Asian Air Traffic Controller did not speak English very well. Now I was not listening the whole time, but he did say something like:
United 895 Heavy, Descend and maintain 5,000 feet.


That is about it, before I turned it off at least.


User currently offlineMusapapaya From United Kingdom, joined Apr 2004, 1091 posts, RR: 0
Reply 14, posted (9 years 5 months 3 weeks 1 day 21 hours ago) and read 3783 times:

The ATC just said descend and maintain at 5000 feet, but they did not say how 'fast' you have to reach 5000 feet really...
What governs that 'speed'?



Lufthansa Group of Airlines
User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 15, posted (9 years 5 months 3 weeks 1 day 20 hours ago) and read 3777 times:

Quoting BRAVO7E7 (Reply 13):
Well, let me say that the Asian Air Traffic Controller did not speak English very well

IIRC, you were going into HKG. They speak very good english there. You should have had no trouble understanding them at all.

ATC assumes a 2000fpm descent rate for descents. Anything more and they will you ask you to "expedite". If you can great, if you can't you just tell them "unable". End of story.

Sometimes ATC will give you a speed to maintain during the descent. In places like HKG they will give you a "high speed" that is above 250 below 10,000'.

However, they will not ask the crew to do something that is against the AFM. If they do, the crew can always decline.


User currently offlineBravo7e7 From United States of America, joined Jul 2004, 1840 posts, RR: 17
Reply 16, posted (9 years 5 months 3 weeks 1 day 14 hours ago) and read 3719 times:

Quoting PhilSquares (Reply 15):
IIRC, you were going into HKG. They speak very good english there. You should have had no trouble understanding them at all.

ATC assumes a 2000fpm descent rate for descents. Anything more and they will you ask you to "expedite". If you can great, if you can't you just tell them "unable". End of story.

Sometimes ATC will give you a speed to maintain during the descent. In places like HKG they will give you a "high speed" that is above 250 below 10,000'.

However, they will not ask the crew to do something that is against the AFM. If they do, the crew can always decline.

Firstly, remember the fuel level was VERY low, so it may have been necessary. Secondly, this was not Kong Kong center, but a different, less busy center.


User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 17, posted (9 years 5 months 3 weeks 1 day 9 hours ago) and read 3683 times:

Quoting Bravo7e7 (Reply 16):
Firstly, remember the fuel level was VERY low, so it may have been necessary. Secondly, this was not Kong Kong center, but a different, less busy center.

If, as you say, it was low fuel, then it would have been Hong Kong radar that directed the descent to 5000'. Otherwise the crew would have stayed at altitude. Descending early, outside of HKG airspace, would have made the problem worse!

Depending on the day and direction of flight, HKG radar isn't all that busy.


User currently offlineBRAVO7E7 From United States of America, joined Jul 2004, 1840 posts, RR: 17
Reply 18, posted (9 years 5 months 3 weeks 1 day 8 hours ago) and read 3670 times:

Quoting PhilSquares (Reply 17):



Quoting PhilSquares (Reply 17):

If, as you say, it was low fuel, then it would have been Hong Kong radar that directed the descent to 5000'. Otherwise the crew would have stayed at altitude. Descending early, outside of HKG airspace, would have made the problem worse!

Depending on the day and direction of flight, HKG radar isn't all that busy.

Whatever it may have been, their English was not all that great.........at all.


User currently offlineAirWillie6475 From United States of America, joined Jan 2005, 2448 posts, RR: 1
Reply 19, posted (9 years 5 months 2 weeks 2 days 3 hours ago) and read 3358 times:

I recently read a trip report on a B744 that detailed a descent from FL280 (ish)to landing in around 5 minutes.

I'm sorry but I highly dubt that, if that were true than the pilot would have had full speedbrakes and had the gears down at 15 thousand feet. The 747 doesn't slow easily. In all my 747 flights the descend began at least 20 minutes before touch-down. It could also be that the pilots had a poor approach planning and decided to let ATC control the approach.


User currently offlineOly720man From United Kingdom, joined May 2004, 6746 posts, RR: 11
Reply 20, posted (9 years 5 months 2 weeks 1 day 19 hours ago) and read 3336 times:

To compare, a recent Air Berlin flight I was on (B738) from MAN-HAM took around 15 mins from cruise at FL390 to landing - according to the inflight screens.


wheat and dairy can screw up your brain
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