Sharp Changes in Altitude and Course After Jet Lost Contact

In this wacky scenario, one must take into account the physiology of the human body at altitude. A decompressed airliner at 35000 feet would affect ALL on board, crew and passengers unless the 777 has a cockpit that is somehow sealed from the rest of the aircraft for which I am not aware. Also, the oxygen system on the flight deck, as well as the walkaround systems used by the cabin attendants, is much much more sophisticated than those plastic drop downs in the passenger cabin. Oxygen would be required once cabin pressure gets above about 15k. In aerospace physiology, a term used is “time of useful consciousness” or TUC....TUC at 35k without O2 is between 15 to 30 seconds, depending on the individual...even less in some, particularly after a rapid decompression. TUC above 40k is maybe 5 to 10 seconds. Above 40k, unpressurized cockpit, 100% oxygen must be administered under pressure through the mask, for the human body to remain functional. The higher you get above 40k unpressurized, the more the pressure is required in the mask, and you must have to forcefully exhale against that mask pressure to get the 02 into the blood in the lungs. These physiological facts are why most airline flight ceilings are in the mid 30s for almost all airline activity. Business aircraft are frequently above 40k, think Mr. Payne Stewart’s ill fated flight. IIRC, above 40k, one crewmember MUST be on oxygen at all times, I.E. MASK ON...in the Stewart incident, not sure those regs were being followed. Also, unless the MA crew had not been breathing 100% O2 since at least takeoff, aka prebreathing in aeromedical physiology, to rid the body of as much nitrogen as possible, a decompression, weather intentional or otherwise to those flight levels, aviator decompression sickness, or the “bends”, comes into play. Particularly if the flight were to continue at those altitudes unpressurized. That is one of the most primary physiological concerns following a decompression at those flight levels...and the need to get to a lower altitude without delay, not just for oxygen supply and TUC concerns, but to also get barometric pressure back on the human body, to keep nitrogen in solution, and not let N2 come out of solution and into bubble form...aka bends. Above 50k, a decompression would cause the human blood to basically “boil” from the lack of barometric pressure on the body as N2 comes out of solution. Thus the reasoning for pressure suits used in all military flights above 50k...U2, SR 71, shuttle etc... Aircraft decompression is usually one of three types. Insidious, a slow leak for instance, rapid decompression, a window or door “popping out”, and explosive decompression, usually caused by total destruction...think shuttle Columbia here, or possibly that Hawaiian airliner that survived the cabin top basically tearing away in flight.. Explosive means the air escaping the vessel, (aircraft) is faster than the speed of sound.

Also, the oxygen system on the flight deck, as well as the walkaround systems used by the cabin attendants, is much much more sophisticated than those plastic drop downs in the passenger cabin.

There is no "walkaround system" used by cabin attendants. At least there was not when I was flying and I was trained on the 777. The rule is "if you see the masks drop, immediately sweep the nearest one to your face, sit down (or get down on the floor) and hold on, because the plane is about to dive." That is why there is an extra mask at every seat row - for cabin crew and/or laps traveling without a seat.

I was trained that you immediately put the mask on because within seconds you will not be able to do so - you lose your coordination and wouldn't physically be able to hold a mask or put it on, much less help anyone else.

You are right that there are 3 types of decompression: slow/gradual; rapid; and explosive, but an explosive decompression does not mean total destruction. UA 811 was an explosive decompression (cargo door ripped loose) that happened at around 22,000 feet; Aloha 243 was also explosive. One of the flight attendants on 811 was hanging on to the stairwell railing for dear life, waving like a flag in the wind. If the event had happened at a higher altitude, she would have been sucked out of the cabin, as she would not have been able to hold on long enough. Explosive decompression is very obvious. Rapid and slow decompression are very dangerous in that you might not realize what is happening (you are still able to breathe in and out) and can be under the effects of hypoxia before you can react.

I had a coworker who was involved in a rapid decompression where there was no explosive event; the masks just suddenly dropped and for the first few seconds, the cabin crew did not react because there was no apparent reason for the masks to have deployed (no bang, no fog, nothing obvious). It wasn't until the rapid descent began that they realized they were in trouble. My friend had damage to her sinus cavity - the lining of her sinus tore loose and caused her horrible problems later on. But immediately during and after the event, she had not felt anything, possibly because she was already under the effects of hypoxia.

I had a coworker who was involved in a rapid decompression where there was no explosive event;

As a former USAF Physiological training instructor, in a training field where we trained pilots, flight nurses, aircrew members,VIPS, guests, etc., the medical affects of altitude on the human body, I probably went through close to a thousand rapid decompressions in hypobaric chambers. We called them RD's....and normally in my days, rd chamber flights simulated an actual decompression from 8k to about 22-25k.. Been away a long time, but I would suppose the training profiles are much the same.......yep. you dont have to clear your ears on the way up, but you do on the way down....sinuses are another matter...I have seen some painful sinus problems with both trainers and trainees.

and in regard to the supplemental oxygen systems aboard a 777, I am totally un-informed, but in my passenger flight history aboard commercial airliners, I have seen "walkaround" bottles stowed in some aircraft...btw, we used them all the time out of Kadena back in the day...while pushin leaflets out the backend of a HerkyBird over North Nam, unpressurized with the ramp down at fl250 give or take a few...usually around 0200 or so local....with an ECM bud about 10k overhead, paintin a hundred radar targets on NV scopes..

Yes, there are walkaround oxygen bottles stored near every bulkhead, but they are for medical emergencies. I mean, you could use it in a decompression if you were able to. If you were to be involved in a decompression, by the time you located a bottle, excavated it from underneath some passenger’s crap that has most likely been thrown on top of it, unclipped it from the wall, removed the mask from the plastic wrap, uncoiled the hose, found the input valve, snapped the hose to it, strapped the mask to your face and turned the flow on, you’d be passed out on the floor. Just snapping the hose into the input can be a challenge in a fully conscious state, as it involves holding aside a small metal clip which wants to snap back into place. I’ve seen some crewmembers take several attempts to do this in recurrent—can’t imagine having to do it while under hypoxic conditions. In addition, the oxygen bottles are not forced air. (Not sure if the passenger emergency masks are forced. I would guess not. I’ve never had to use one, fortunately.)

Along with the medical oxygen, the AC would also contain PBE for firefighting. Those contain 15 minutes worth of oxygen, but that is a hood you wear over your head … again, pretty difficult to attain and get into within 10 seconds before hypoxia.

And yeah, I know what you mean about utilizing oxygen bottles. It truly is the cure for…ahem… exhaustion. Personally, I preferred just slipping up to the cockpit and taking a hit off theirs. Nothing to write up. ;-)

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