Originally Posted by
Ftrooppilot
Diluter-demand oxygen systems can be used up to 40,000 feet. In a pressure-demand system, oxygen in the mask is above ambient pressure, permitting breathing above 40,000 feet. Because the pressure inside the mask is greater than the pressure around the user’s torso, inhalation is easy, but exhalation requires more effort. Aviators are trained in pressure-demand breathing in altitude chambers.
1. Which system do the 777 pilots have - diluter or pressure demand ?
2. Discounting former military pilots, what % of airline pilots get altitude chamber training and high altitude physiology training ?
3. How big an IAS envelope is there between stall and Mach tuck in a 777 at 45,000 ft ?
My questions don't imply anything - just looking for answers.
Civilian pilot high-altitude training and equipment is intended to get you DOWN, in a big hurry, from a high-altitude cabin. In that scenario, any DCS would hopefully be mitigated by the rapid decent to lower altitude (ie re-compression). This assumes only a few seconds spent before hustling on down.
It's not designed to go the other way...very high odds of serious or debilitating DCS if you went quickly from normal cabin alt to 40K+ and stayed there for any length of time. Only work-around would be to pre-breath pure O2 or an exotic diving mixed gas for an extended period (probably impractical in this scenario...the other guy would inquire what you're up to). Military pilots would likely know this (as would experienced divers/parachutists), but civilian pilots might not understand that. They might think their mask (on 100% or pressure-demand) would keep them safe. The mask would keep them supplied with O2...while the N2 in their blood boiled.