What is the maximum altitude for starting the Auxiliary Power Unit (APU)?

The maximum altitude for starting the Auxiliary Power Unit (APU) is set at 30,000 feet MSL. At this altitude, the APU is designed to operate effectively within its specified limits. Starting the APU at this altitude ensures that adequate air pressure and temperature conditions are present for proper operation, which is essential for the optimal performance of auxiliary power systems.

Operating beyond this altitude may result in insufficient performance, leading to potential operational issues or failure to start. The manufacturer's specifications for the APU ensure that all operational parameters are adhered to, thereby ensuring safety and reliability.