What happens to the APU’s oxygen supply during engine start procedures?

During engine start procedures, the APU (Auxiliary Power Unit)’s oxygen supply is indeed monitored closely and can be affected by the demands of the starting process. The correct response reflects the fact that during engine starts, particularly in certain aircraft operations, the APU's functions may be reallocated to support cabin pressurization, especially when the engines are not yet providing thrust or power.

This redirection is crucial for maintaining a safe and comfortable environment for crew and passengers while the main engines are being ignited. The APU is primarily responsible for providing electrical power and pneumatic pressure, and strategic management of its systems, including the oxygen supply, is essential to support other aircraft systems during these procedures.

Thus, understanding how the APU interacts with other systems, particularly in critical startups, is important for aircrew operations and safety protocols.