Emergency Descent from above FL410.

[Paradise Lost]

On some a/c an "Automatic Emergency Descent" mode is available either as an option or as standard equipment. What happens to you physiologically if you experience a catastrophic decompression at levels above FL410, makes depressing reading and shouldn't be considered before eating!
If you just consider the "useful time of consciousness" as 9-12 seconds, and that your O2 mask is certified to supply 100% oxygen under pressure UP TO 41,000 ft (!), then I am puzzled why the certifying authorities (FAA/EASA) would ever allow any a/c to operate above that level without an automatic emergency descent mode mandated.
It's a moot point whether you would wish to survive in a vegetative state thereafter, but at least give us a chance.

[Grum]

Jeez i'm going to have to look up these 'physiological effects', didn't realise you could end up in a vegetative state afterwards.

Anyway, my aircraft does not have an emergency decent button and during a sim debrief the other day the instructor had this to say; Instead of diengaging and getting down as quickly as possible why not keep the AP on and simply roll ASEL down to 10000 or MSA and use the pitch wheel or TCS. Sure you are not going to descend at the same high rate but at least you are going down and if you were to pass out you know the aircraft will level off. I hasten to add that we have auto throttles which would kick in to prevent a stall.

There was a thread a while back about a kingair with a cracked windshield, the crew hit DUMP to relieve the pressure, diengaged and descended, they both passed out and the co-jo regained consciousness around 8000ft inverted! :ok:

[smallfry]

This is a common misconception
Firstly,
The masks are designed for continous use upto a CABIN altitude of 41000. In the event of a decompression, the cabin would rise up, but unlikely to be sitting at 41000 for very long before you managed to get the masks on.
Thus aircraft can be certified to fly above 41000' with these masks, as long as the manufacturers have demonstrated that the aircraft can be descended from the required FL to 10000' within a certain time frame (4 minutes). This is why your emergency descent drills require you to follow manufacturers guidelines for rapid descent, regarding use of speedbrakes and or gear or whatever. They have had to prove the aircraft can do it, and this might require a specific configuration.
Secondly,
Yes, You would pass out, (without the masks), eventually, but if the aircraft remained under control ( ie EDM or autopilot in VS/FLC/VNAV to a selected Altitude - normally 10000' if MSA permits) then you would come round again (unless you had had a secondary complication, like a heart attack or something). You would have a headache, and maybe a bit of baro trauma, but I think Vegetative state is over-reaching it a bit.
Apart from a big fright, you should have no long term damage.

[G-SPOTs Lost]

EDM is great if you are conscious enough to close the TL's and deploy the speed brake otherwise you'll fly level.

It is a freaky thing to watch though when demostrated in the sim, my type (C680) has a tremendous tendency to slow when level at 14000 to the stick shaker at which point it lowers the nose to build speed and then repeats this until you hit the ground, from FL400 it gives you around 15 mins to come around and take control.

Memory item is still to commence the emer descent manually or with the AP engaged TCSing to Mmo with 10 panels and idle power i.e. you DONT wait for EDM

[galaxy flyer]

Also remember, we are speaking of rapid decompression, not explosive! The cabin is coming up at a high rate, but not near instantaneously. Loose both packs in my plane at FL 410 and you can pretty much sit there watching the cabin come up slowly. FAR 25 doesn't protect against explosive decompression. BTW, the FL 510 cert. test opens a valve the size of the cabin window to simulate loss of a window, the cabin there rises pretty slowly.

GF

[Paradise Lost]

Also remember, we are speaking of rapid decompression, not explosive!
Actually I was talking about explosive decompression, a la Aloha 737 type!
I also perform Airworthiness test flights during which max. diff pressures are checked, cabin leak rates at max. diff are monitored, Cabin warning horns/mask drop-outs are tested. Under EASA requirements, the cabin leak rate is not to exceed 1,500 fpm, and is commonly in the order of 9-1,200 fpm thus giving nearly 10 minutes to descend to a safe level in the event of LOSS of pressurisation!
However if you are above FL410 at max. diff and the "bad repair" comes undone, or the corrosion from the lav spillages sheds a chunk of fuselage, and you have an "explosive" decompression, then time of consciousness and even survival are in the balance.
Regarding what happens to you physically, I merely extracted that from the PPRuNe medical section, and it wasn't good news! A lot of bleeding and plenty of oxygen starvation to the brain...... http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/icons/x.gif

[hunterboy]

I thought that the FL410 rating on the mask was to do with the maximum partial pressure of O2 that will be supplied (at 410) using a demand mask.
To get more than that amount of o2 into your lungs would require a different type of mask (such as those on Concorde)

[smallfry]

While I appreciate your concern and realise you are being rhetorical not pedantic,you and I both know that in reality you will have a lot of unhappy owners if you fly your Global at less than FL410!
We could all worry about everything... What if the engines run out of oil at 30W? What happens if the Galley catches fire over the Pacific? Personally I am more concerned about a Fire than Depressurisation. Sometimes you have to have a bit of faith in your Maintainance team, and your preflight....
If you had a explosive decompression it is a very bad day.

[doubleu-anker]

Remember this. Just because it is legal, does not necessarily mean it is safest practice. There are commercial pressures bought to bare on decision making, before authorities come up with a regulation.

I will never consider an "enroute alternate" for F/P purposes, for example, as I think it is too risky. I. E., one more door closing behind you. However, in certain situations it is legal. (yes I have carried out long range operations)

Common sense and risk management can play a part to reduce the dangers.