How long does the APU fuel shutoff valve need to close after the APU is shut down?

The APU fuel shutoff valve is designed to close in a specific timeframe after the APU has been shut down to ensure safety and proper operation within the aircraft systems. In this case, the correct timeframe for the APU fuel shutoff valve to close after the APU is shut down is 60 seconds. This allows sufficient time for any residual fuel in the lines to be cleared and ensures that the system is fully depressurized, effectively minimizing the risk of fuel leaks or potential fire hazards that could occur if fuel flow were to continue after shutdown.

The 60 seconds is a critical safety measure emphasized in operational procedures, as it strikes a balance between system responsiveness and ensuring that residual processes have completed. Understanding the timing of the valve's operation is important for pilots and technicians to follow standard protocols during and after APU operations, ensuring both safety and compliance with maintenance practices.