When an airliner loses all engines while at cruising altitude, two things happen:
- The plane is a glider. It will descend no matter if you want to or not.
- The cabin pressure is no longer maintained. Although the valves are closed automatically, they are not air tight - air will slowly leak out until the air pressure is equal to the atmospheric pressure outside.
My question is, which one happens faster? Are the valves able to maintain cabin pressure until the plane has descended to 10,000 feet, or will the oxygen masks deploy before the pilots can complete their descent at best glide speed?
EDIT: For the purpose of the question, let's assume it's s fuel exhaustion and ignore the APU. I'm specifically interested to know if the crew would encounter a situation where they have to choose between oxygen and best glide.