Topic Author
Posts: 2276
Joined: Thu Aug 05, 1999 1:42 pm

Rapid Decompression

Sat Oct 30, 1999 8:27 am

To the airline pilots out there:

Please don't think relates to what happened to Payne Stewart, I had this question itching at the back my neck for a time now.

How are you trained for rapid/explosive decompression? If the decompression doesn't kill you won't the temperatures?

How come the 'quick donning' masks usually take longer to don than the time of useful consciousness?

Are these masks the same as the ones used in the event of a smokey inflight fire?


Neil Harrison
Posts: 1066
Joined: Fri Mar 16, 2007 1:29 pm

RE: Rapid Decompression

Sat Oct 30, 1999 9:51 am

All transport category commuter and airline (probably corporate jet ops too, but don't know for sure) train for rapid decompression, and onboard fires/smoke.

Quick donning O2 can be put on within seconds - there is a mandated time frame by regulation both in Canada and the USA, but I don't know what it is other than you have to be able to put it on and activate it with one hand.

The chances of explosive decompression on any jet aircraft are very, very remote. Explosive decompression would occur on a smaller jet with the loss of a door or fuselage failure as a result of explosion, for instance. On a large jet aircraft like a 747, the loss of a cabin door would result in a rapid decompression at the further most point from the door, increasing in intensity to within immediate vicinity of the door. Concurrent with the loss of pressure, the airplane continues to try and pressurize itself by closing the pressurization outflow valve.

With the last paragraph in mind, it changes the situation in the cockpit from needing only seconds to react to a period somewhat longer. Of course, should the failure causing loss of pressurization be from a blown out cockpit window, then things would be a lot more exciting (...NOT!), er how about urgent! The cockpit windows are the thickest and most reinforced on the airplane, partially for that reason.

When an aircraft suffers a rapid decompression, the pilots know about it instantly due to the feeling in their ears - a very distinct physiological reaction. Additionally, when the cabin pressure rises above 10,000 feet, alarms go off in the cockpit.

So the chances of getting a -60C blast of cold air in the face are one in a gazillion. At any rate, the aircraft must be able, and crews are trained to get the aircraft down below 14,000 in 4 minutes or less, from the highest certified altitude.

Many cockpit O2 masks require a supplementary smoke goggles in the event of smoke/fire. Some masks integrate the two, but nonetheless both types are not usually portable.

For fires, separate Personal Breathing Equipment (PBE's) are now installed. They are tight fitting hoods with a llittle Oxygen generator inside - good for about 15 minutes.

If you need to do both the above procedures at the same time (like with Swissair 111 last year), you're having a really bad day.

Once again, deepest condolences to the family and friends of all onboard Payne's aircraft. Rest in Peace.

Best Regards,

Posts: 11191
Joined: Tue Jun 15, 1999 11:29 am

RE: Rapid Decompression

Sat Oct 30, 1999 9:57 am

The quick-don oxygen masks have be able to be donned within 5-seconds (if my memory of regs serves). You'd have to be pretty dawgone high (higher than most airliners fly) to have a TUC of 5 seconds. Sorta defeats the purpose otherwise. The quick-don masks are *not* the same ones as the smoke masks.
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
Topic Author
Posts: 2276
Joined: Thu Aug 05, 1999 1:42 pm

RE: Rapid Decompression

Sat Oct 30, 1999 12:34 pm

The reason why I asked about that last question was because I was looking at a pic of a pair of DC-9 masks and those look cumbersome. The NTSB report from the Valujet crash was pretty damning about the quick donning masks, not being quick donning enough...

Again, thanx to all who contributed to this question.

- Neil Harrison
Posts: 448
Joined: Thu Jul 29, 1999 8:12 am

RE: Rapid Decompression

Sat Oct 30, 1999 1:31 pm

As a side note, the FARs require one pilot of ALL pressurized aircraft flying above 40,000 ft to be on O2 at all times at or above that altitude. That is one of the reasons why commercial, non-supersonic flights don't usually go above 39,000.

This means that if Payne Stewart's pilots followed the rules religiously (and we have no reason to be lieve they didn't) whatever happened to them was prior to 40,000.