View Full Version : emergency descend vs rapid descend

29th Aug 2010, 23:35
can anyone explain in details? thanks....:O

29th Aug 2010, 23:50
Well, an emergency descent is one where you're descending for safety and a rapid descent is one where you expedite a normal descent procedure.

A lot of pilots on here believe that every emergency descent is a rapid descent, but this is not true. A rapid descent varies from aircraft to aircraft (on the A340, it's >3500fpm). You wouldn't carry out a rapid descent if you lost all engine thrust, would you?

Pro Spin
29th Aug 2010, 23:59
Another example to help differentiate between the two is an explosive decompression. The crew would initiate an "emergency descent" but if they suspect airframe damage they may consider maintaining the current speed and aircraft config (i.e: no speed brake or gear) to avoid further damage. On the A320 this would give a rate of descent of around 1500-1800fpm - an emergency descent but not a rapid descent.

Hope that helps.


Pro Spin

Teddy Robinson
30th Aug 2010, 00:01
being pedantic about the question :

Emergency descent is in my experience a memory drill to be used in a cabin hi-alt / loss of cabin pressure. The contents of this drill are typically :

crew masks don, flow rate 100%, crew communications establish, announce emergency descent, thrust levers flight idle, speed MMO/vMO, airbrakes out
check MSA , inform atc etc ...

Rapid descent ... as above but with no emergency, therefore no drill and no masks and with clearance from or at the request of atc.

30th Aug 2010, 00:40
Another example to help differentiate between the two is an explosive decompression. The crew would initiate an "emergency descent" but if they suspect airframe damage they may consider maintaining the current speed and aircraft config (i.e: no speed brake or gear) to avoid further damage. On the A320 this would give a rate of descent of around 1500-1800fpm - an emergency descent but not a rapid descent.

Why wouldn't you use the speed brake? The configuration you're looking at it is little different to a normal descent.

30th Aug 2010, 08:42
Mr Deux /Teddy

If you suspect airframe / structural damage, the additional buffetting caused by deploying the speedbrakes and/or gear, could further damage the aircraft structure and lead to an in-flight break-up.

For that reason, if you suspect structural damage it is advisable to maintain present IAS for the descent to minimise the changes to the loading.

Yes, the descent will take longer, but it is deemed safer.


In both the above cases you would be on oxygen - I think you need to do some more revision.

Pro Spin
30th Aug 2010, 10:09
For me, oxygen masks are there for 1 reason - a lack of breathable air in the flightdeck (decompression above FL100 or smoke).

I can see a number of examples where you can perform a rapid descent but not require oxygen masks (e.g: APU Fire, Cargo Fire, red bomb threat).

Oxygen masks severely impede cockpit and cabin communications and therefore I personally would only use them for the above mentioned flightdeck environment issues (smoke or lack of air)


Pro Spin

galaxy flyer
30th Aug 2010, 17:00
In the 60's, there was a 707 that suffered a bomb explosion, damage was significant and the crew did the "high dive" emergency descent, as practiced in training. The plane broke up in the upper teens, IIRC. OTOH, a AF C-141 had aft door failure, most of the crew were rendered semi-conscious from the rapidity of the decompression at FL 410, I believe. The co-pilot wasn't sure what tp do but by then training mentioned structural failure and he did a gradual descent and saved the plane and crew. Lockheed, who rebuilt it, was positive that the plane would not have survived a high speed descent.


31st Aug 2010, 03:51
in an extension to that......

With the airplane at cruise altitude and speed, and an emergency descent became necessary....

Would you go idle, speed brakes, slow to gear extension speed, extend the gear, then descend at a rather high rate...or,

Would you go idle, speed brakes, and immediately start the descent, but necessarily at a lower rate of descent.


galaxy flyer
31st Aug 2010, 04:27
Depends on type, older ones did slow to gear extension, DC8s used the thrust reversers, as I understand it, we did in the Galaxy.


Teddy Robinson
31st Aug 2010, 07:52
Structural : absolutely, if suspected, been there done that @ 210 kts, no airbrake.(and no oxygen) Don't think that was part of the question though ? or perhaps as the term "rapid descent" does not appear in our FCOM I have taken another tack

Routing in from the south to GVA, they keep us high over departing traffic trying to make sector safe, and (usually) give the option of a high rate to make the approach fix OR the full procedure with possible holding.
So long as the weather is not an issue and the cabin is secure, it helps atc, and helps us
It's rapid, but it is not an emergency, that was my point.

Pro-Spin .. I take your point as well, our FCOM says expedicious rather than rapid for those circumstances, perhaps they should review the terminology used in our documentation.

7th Sep 2010, 21:42
thanks for the infos guys.... as we know,

emergency descend
- initiated due to rapid decomp or smoke
- actions are, oxy mask on 100%, comm est,
PF - alt window 10k, hdg off airways, speed vmo/mmo or current
speed if structural damage is suspected, thrust idle, spd
brake out (careful if structural damage, avoid high vib).
PNF - seatbelt on, lights on, pax oxy on (cabin alt 14k or more),
ignition start (airbus), sq 7700, mayday call.
rapid descend :-
- alt window (any altitude, since its not decomp), speed close to
vmo/mmo, thrust idle, speedbrake out.

am i right, or am i right?? can someone add somewhere that i might missed?? thanks.

7th Sep 2010, 22:31
I'm wondering whether the trained procedure for emergency descent is to use the autopilot or fly it manually? If autopilot, what mode? How is transition through the altitude of the Vmo/Mmo corner handled?

7th Sep 2010, 22:52
if u have automation, why not? set the speed to mmo, and once it pass the transition level, it will maintain vmo.....
if u dont have automation, descend manually, and use your PNF to set whatever target that u want....:ok:

8th Sep 2010, 04:44
Thanks you for the post.
Hi guys, Im a newbie. Nice to join this forum.

Pontius's Copilot
8th Sep 2010, 08:37
PF - alt window 10k, hdg off airways,

Not in the UK please ...
http://www.nats-uk.ead-it.com/aip/current/aic/EG_Circ_2009_P_052_en.pdf (http://www.nats-uk.ead-it.com/aip/current/aic/EG_Circ_2009_P_052_en.pdf)
"...Therefore, if able, pilots should remain on the assigned route or track whilst carrying out the emergency descent; unless to do so otherwise would endanger the aircraft ..."

8th Sep 2010, 09:19
PF - alt window 10k, hdg off airways

1. Everyone seems to go for 10,000. Not a very good idea over the Alps or anywhere else that terra firma extends above 6000.

Remember that you are sitting there with Standard Pressure Setting on the altimeter and if enroute probably don't have the local QNH to hand.

Descend to 10,000 on 1013 when the QNH is 970 and you will actually be at 8710 (+/-) and the required separation from terrain at this level is 2000ft............unless you want to add other issues eg turbulence, EGPWS warnings etc etc into the mix. OK you can argue that in an emergency as long as you don't hit the ground than all is OK. but descending to 8710ft over the alps is not a good idea.

2. Don't try to remember what one country would like you to do. If you do then that is nice but it is not essential in an emergency

TCAS to "below" and avoid the traffic as best you can remembering that range is more accurate than bearing.........which will be easier if you don't stick to an airway centerline!!

3. Finally, don't forget that many (most?) aircraft can cruise safely at 25,000ft for some time with everyone on oxygen. As far as I am aware the 25,000 limit is based on the yellow masks used by pax........so if you have established everyone on oxygen then what is the rush to get down in the weeds?

Can't see myself hanging round freezing at 25,000 for very long if I can get down but one has to remember that a screaming dive to anything below 25,000 (away from Everest and the like) is going to have as many "not so good" points as good points.

8th Sep 2010, 17:04
And don't forget before you take your O2 mask off that it is pressure altitude that determines whether you have sufficient partial pressure of O2.

8th Sep 2010, 17:15
FAR calls for cabin altitude to never exceed 40K feet and to not exceed 25K feet for more than 2 minutes. This has to be met for an expected fuselage hole size. A single cabin window is usually considered. This can become an upper bound on passenger window area. Cockpit windows are strong enough to not have to be considered (testing with the chicken gun shows compliance there).

8th Sep 2010, 17:27
When descending on autopilot the MCP speed window will transition from Mach to Vcas when passing through the Mmo/Vmo altitude. For the most rapid emergency descent the crew will have dialed the window up to Mmo. At the Mmo/Vmo altitude the speed window will transition from Mmo to a Vcas value that represents a nominal descent speed (less than Vmo). In order to continue a rapid descent profile, the crew will have to dial the speed window up to Vmo.

14th Sep 2010, 19:47
thanks pontius and DFC for the additional infos... FCheng, will definitely try it on my next visit to the sim... thats why they ask us to fine tune and crosscheck what we've set up for the descend...:O

16th Sep 2010, 16:36

Emergency Descent only as procedure is not a Distress, so you cannot use the signal MAYDAY. Emergency Descent is an Urgency, for that reason you must used the signal PAN PAN PAN. Obviously, if you have to carry out an Emergency Descent due to an engine failure because of an explosion inside engine followed with decompression and hydraulic failure…you need to use MAYDAY MAYDAY MAYDAY

According to ICAO DOC 7030 when an aircraft operated as a controlled flight experiences sudden decompression or a (similar) malfunction requiring an emergency descent, the aircraft shall if able:
1. Initiate a turn away from the assigned route or track before commencing the emergency descent;
2. Advise the appropriate air traffic control unit as soon as possible of the emergency descent;
3. Set transponder Code to 7700 and select the Emergency Mode on the automatic dependent surveillance/controller pilot data link communications (ADS/CPDLC) system, if applicable;
4. Turn on exterior lights;
5. Watch for conflicting traffic both visually and by reference to ACAS (if equipped) and;
6. Coordinate its further intentions with the appropriate ATC unit.
Keeping in mind that the aircraft shall not descend below the lowest published minimum altitude which will provide a minimum vertical clearance of 300m (1000ft) or in designated mountainous terrain 600m (2000ft) above all obstacles located in the area specified.

* Personal note: In an Emergency Descent as number 7. I would switch ON Engine Anti-Ice because you could be very busy to realize that you are in icing conditions (specially performing an Emergency Descent during nights)
Finally, according to some planes if available, Speed Brakes have to be used to carry out and Emergency Descent, IF NOT, you cannot develop an Emergency Descent properly, Can you? The question about Structural Damage Known or Suspected, well it must be answered after using the Speed Brake. If the answer is Yes, you may dictate more conservative speed profiles or entry maneuvers, but you need Speed Brake to descend (drag)

In a rapid descent, which is a normal procedure, you should use the Speed Brake if available.

About the whole procedure in an Emergency Descent, you have to check your FCOM and QRH