View Full Version : Emergency descent rates

Bern Oulli
15th Jul 2002, 18:03
I am an air traffic control instructor, rewriting some radar exercises (i.e. deleting the Vikings Viscounts and Vanguards!). One of the scenarios requires an emergency descent following cabin de-pressurisation. Given some typical commercial jets and turbo-props, what rate of descent would you guys expect to achieve from cruise to FL100 ish? The boffins programming the sim seem to think that expedited ROD + 10% is OK - I say a lot more. Give me some figures related to type guys, then I can re-program a boffin. Cheers

15th Jul 2002, 18:10
between 4000 and 4500 ft/min should be the average...

15th Jul 2002, 18:46
I would hope that I should be able to get about 6000fpm out of a 757/767. Of course there was an aircraft many, many years ago that could do around 26,000fpm but I shall not mention its name here as it is forbidden with in the company!
I have heard as well that if you sideslip a 75 it simply falls out of the sky...whether you can get it out of the sink of course is another matter...
Kind regards,
yours aye,

15th Jul 2002, 19:15
In the C525 would expect to get 6000/7000 fpm
:cool: :cool:

15th Jul 2002, 20:26
Airbus 6000+ ish give or take.

16th Jul 2002, 03:43
All the aircraft I have flown have been able to "clock" the VSI at over 6000 fpm on an emergency descent. The Westwind (which has a very good set of airbrakes) I once timed at 12,000+ fpm, so your expidite ROD + 10 % may be a little conservative.

Bern Oulli
16th Jul 2002, 07:24
Thanks a lot guys, all these figures are well in excess of what the sim is programmed to do. I shall depart the fix and reprogram a programmer!

Be careful up there.

16th Jul 2002, 13:05
Bern Oulli

Under normal operations we were kept at cruise level beyond descent point due outbound traffic at LPA last night. When clear, winding speed up to 340Kt in "open descent" (i.e idle thrust) gave peak descent rate >6000 fpm with an average of about 4000fpm down to FL 150 to get us back on profile, with use of speedbrake (A320). Pressurisation system copes fine with these rates, so no ear popping.

as an aside, for an Emergency descent our QRH drill says to "maintain or reduce speed if structural damage" which would obviously reduce the descent rates, whereas for a straightforward pressurisation failure (non structural) we will wind the speed up to max for highest ROD which probably "averages out" to 6000-7000 from FL350 down to FL100.


Young Paul
16th Jul 2002, 13:59
It would vary - and it also flattens out as the air thickens. I would suggest that, to be realistic, you go for a random figure between 4000fpm to 7000fpm, reducing to 1500 to 3500 close to FL100.

Bern Oulli
16th Jul 2002, 18:54
Thanks one and all. This is approach radar that we are simulating, the idea being to present the student with an a/c descending at a high rate into his crowded bit of airspace (FL120 downwards) with not very much notice from area control. We do not intend to complicate the issue at the moment with structural damage as well.

There are limits to what the computers will do (so the boffins tell me) so those ball-park figures are fine. Mind you, we had a PA28 up to mach 3.0 yesterday. No structural damage either!

Thanks again.