above its ceiling for any length of time and there's only one reason for doing that to incapacitate, quite frankly kill, get rid of all the passengers in the back. you depressure rise the airplane and you're on an oxygen mask. and that would explain coming down to a more comfortable altitude. >> this is a technical question, but do masks nod come down to people in the back of the plane? >> even if they come down, those masks are only designed to give you enough oxygen to sustain you without any brain damage from the highest altitude that you're authorized to fly a jet 43,000 feet down to 14,000. they're never designed to stay up there. consequently they'll run out of oxygen at 10, 15 minutes at the maximum. on top of that, there were walk-around bottles that the crew may get on. those are breathable even up to