What is the typical cycle time for an APU's start and cool down?

The typical cycle time for starting and cooling down an APU is indeed around 10 to 15 minutes. This duration is crucial for ensuring the APU operates within safe and efficient parameters. The start-up process involves various checks and sequences that allow the APU to reach its operating conditions, and the cooling down phase is equally important as it helps prevent overheating and prolongs the lifespan of the unit.

Understanding that the APU needs time to stabilize after starting and to properly shut down is vital for maintenance protocols and operational efficiency in aircraft systems, such as the C-5. Moreover, adhering to this timeframe contributes to the overall reliability of the power unit, ensuring it is ready for subsequent uses.