Question id 444 - Aircraft General Knowledge - Airframe, Systems, Powerplant - ATPL - Airline Transport Pilot license

Only portable oxygen bottles.
Two independent oxygen systems, one for the flight crew and one for the passenger cabin.
Two oxygen systems, both supplying the flight crew and the cabin together.
One oxygen system supplying the whole aircraft.

Training tests and timed exam simulations ATPL - Airline Transport Pilot license