AeroTech
The questions you ask? Your questions do not appear aircraft specific which makes it very difficult to answer.....
747 all engines flame out and you are worried about decompression..No 747-400 have APU inflight start so forget that.
Surely the rate of decent depends on the amout of oxygen available. ie Some 747s have extra oxy fitted for crew and pax so when flying over mountainous areas they can remain at altitude longer until a safer altitude becomes available..no cumilous granitous around..
APUs rarely if ever supply bleed air in the air. They provide electrical power
On a unpressurised ferry flight...The airconditioning pac s will still be running just the out flow valves open ...no diff pressure but plenty of flow thru...same as when the aircraft is on the ground..pac s running..
Crew oxy masks not pressure fed? How do you think they get oxy to the mask.
ETOPS DIVERSION. ETOPs is flying on one engine. one engine will provide enough bleed air to keep the aircraft pressurised. No oxygen is required. If you lose an engine and have a decompression. Multiple failures it is a very bad day and if you are on the edge of your ETOPS range you may not make it to your designated diversion airfield.
Why so many questions..What are you learning?