sevenheavy
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B744 High Rate Of Descent

Sat Apr 02, 2005 9:57 pm

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.
 
PhilSquares
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RE: B744 High Rate Of Descent

Sat Apr 02, 2005 10:53 pm

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.
Fly fast, live slow
 
mandala499
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RE: B744 High Rate Of Descent

Sat Apr 02, 2005 10:59 pm

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 !
 
JAM747
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RE: B744 High Rate Of Descent

Sun Apr 03, 2005 12:44 am

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?
 
PhilSquares
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RE: B744 High Rate Of Descent

Sun Apr 03, 2005 12:53 am

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.
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Starlionblue
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RE: B744 High Rate Of Descent

Sun Apr 03, 2005 2:30 am

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."
 
bravo7e7
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RE: B744 High Rate Of Descent

Sun Apr 03, 2005 6:54 am

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.
 
mandala499
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RE: B744 High Rate Of Descent

Sun Apr 03, 2005 8:08 pm

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 !
 
BobbyBoeing
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RE: B744 High Rate Of Descent

Mon Apr 04, 2005 4:28 am

Hello all,

does anybody know, when this happened? I'm interested in the exact date!
 
Newark777
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RE: B744 High Rate Of Descent

Mon Apr 04, 2005 4:49 am

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?
 
RightWayUp
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RE: B744 High Rate Of Descent

Mon Apr 04, 2005 5:06 am

And don't forget about the pressurisation, very uncomfortable!
 
musapapaya
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RE: B744 High Rate Of Descent

Mon Apr 04, 2005 3:52 pm

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
 
wing
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RE: B744 High Rate Of Descent

Mon Apr 04, 2005 5:09 pm

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.
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bravo7e7
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RE: B744 High Rate Of Descent

Tue Apr 05, 2005 5:33 am

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.
 
musapapaya
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RE: B744 High Rate Of Descent

Tue Apr 05, 2005 7:08 pm

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
 
PhilSquares
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RE: B744 High Rate Of Descent

Tue Apr 05, 2005 8:15 pm

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.
Fly fast, live slow
 
bravo7e7
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RE: B744 High Rate Of Descent

Wed Apr 06, 2005 2:24 am

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.
 
PhilSquares
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RE: B744 High Rate Of Descent

Wed Apr 06, 2005 6:45 am

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.
Fly fast, live slow
 
bravo7e7
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RE: B744 High Rate Of Descent

Wed Apr 06, 2005 7:43 am

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.
 
AirWillie6475
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RE: B744 High Rate Of Descent

Tue Apr 12, 2005 1:13 pm

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.
 
oly720man
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RE: B744 High Rate Of Descent

Tue Apr 12, 2005 8:32 pm

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.
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