Do not leave the aircraft unattended more than __ with the APU running.

Do not leave the aircraft unattended more than __ with the APU running.

• A. 2 minutes
• B. 5 minutes
• C. 10 minutes
• D. 15 minutes

Answer: (B)

Running the APU on the ground provides the power and air you might need, but leaving the aircraft unattended while it’s running introduces risk. Any fault—overheat, abnormal EGT, oil leak, or a fire indication—could develop while nobody is watching, and a quick response is unlikely. A five-minute limit strikes a balance: it’s long enough to perform quick tasks or checks, but short enough to ensure you’re nearby to detect and address problems or to shut the APU down if no issue is present. If you need to be away longer, the safe practice is to shut the APU off and switch to external power or arrange for monitoring, rather than extending unattended operation. The other timeframes either hinder routine operations or increase hazard and resource use by allowing a longer window for potential problems to go unnoticed.

Running the APU on the ground provides the power and air you might need, but leaving the aircraft unattended while it’s running introduces risk. Any fault—overheat, abnormal EGT, oil leak, or a fire indication—could develop while nobody is watching, and a quick response is unlikely. A five-minute limit strikes a balance: it’s long enough to perform quick tasks or checks, but short enough to ensure you’re nearby to detect and address problems or to shut the APU down if no issue is present. If you need to be away longer, the safe practice is to shut the APU off and switch to external power or arrange for monitoring, rather than extending unattended operation. The other timeframes either hinder routine operations or increase hazard and resource use by allowing a longer window for potential problems to go unnoticed.