What is the maximum altitude for using APU bleed?

The maximum altitude for using Auxiliary Power Unit (APU) bleed air is established at 15,000 feet. At this altitude, the APU can effectively provide bleed air for systems such as air conditioning and engine start, which are critical for maintaining cabin pressure and comfort, as well as powering up essential systems before engine startup.

Above this altitude, the efficiency of the APU decreases, and operational limitations may either restrict or prohibit the use of APU bleed air to ensure safety and performance standards are met. This altitude limitation helps to maintain adequate system functionality and prevents potential issues that could arise from relying on the APU at higher elevations where performance may be compromised.