What is the maximum altitude for using APU bleed air?

• A. 25,000 ft
• B. 30,000 ft
• C. 20,000 ft
• D. 15,000 ft

Answer: (A)

APU bleed air provides the pneumatic power for the environmental control system and for starting engines when needed. The system must deliver enough pressure and flow to keep the packs supplying conditioned air and to maintain cabin pressurization. As the airplane climbs, ambient pressure drops, and the APU’s bleed air compressor has a finite capability to produce the required pressure. That creates a published ceiling for reliable bleed air use. For this setup, the maximum altitude is 25,000 feet. Above that, the APU typically cannot guarantee the needed bleed air pressure, so you’d rely on other sources (like engine bleed air when engines are running) instead.