Is another start attempt permitted after an unsuccessful APU start attempt in the air?

The correct response is that another start attempt is not permitted until after landing. This procedure is rooted in safety protocols to prevent potential hazards associated with repeated starting attempts of the Auxiliary Power Unit (APU) in-flight, which could lead to complications such as overheating or damage to the APU.

When an APU fails to start, it usually indicates an underlying issue that could be exacerbated by immediate retry attempts. Allowing for a cautious approach by postponing any further attempts until safely on the ground helps ensure that the operation remains within safe parameters. This protocol mitigates risks not only to the aircraft itself but also to the crew and passengers on board, considering that a malfunctioning APU could significantly impact power availability or environmental controls in the aircraft.

On the other hand, initiatives such as attempting to restart immediately or after a specific waiting period may seem practical but overlook the crucial aspect of safety management in flight operations. Addressing technical issues promptly is essential; however, prioritizing safe operations by avoiding unnecessary attempts in the air is paramount.