What is the maximum certified operating altitude for the APU?

The maximum certified operating altitude for the Auxiliary Power Unit (APU) is indeed 37,000 feet mean sea level (MSL). This altitude indicates the highest point at which the APU can reliably perform its functions, which typically include providing electrical power and bleed air for air conditioning and starting the main engines while the aircraft is on the ground or in flight.

Operating the APU above this altitude could lead to performance issues, such as insufficient airflow or power generation, due to the thinner atmosphere, which can affect proper combustion and cooling. Therefore, 37,000 feet is established as the upper limit for safe and effective APU operation, ensuring the unit functions as designed for various operational requirements.