when the air pressurized air in the plane gushes out into explosive force. those inside the plane need to get to an oxygen mask immediately or they suffer badly from asphyxia. on the two test flights. on one of the test flights, maximum altitude, 43,000 feet and the pilot just got it down, and even then, four of the test crew had to be taken to hospital to be treated for in diving terms called the bends, because they didn't get to their oxygen masks in time. now, it's very fortunate that that happened at that stage in the flight test program, and it exposed a flaw in a valve in the air conditioning system in the belly of the plane. that was rectified then, and there's been no recurrence of that since, but this simply shows to you that there was no redundancy for that failure. it was call add single point facial, highly unusual and no backup. and officers ensured since that can't be repeated. the whole purpose of test