APU bleed air can be used in flight up to what altitude?

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

Answer: (B)

APU bleed air provides pneumatic power for engine starts and the environmental control system, but the air the APU can deliver becomes less reliable as you climb. To ensure a stable, adequate supply without overloading the APU, aircraft systems set a flight-use ceiling for APU bleed air. That ceiling is commonly 25,000 feet, so in flight you’d typically use the APU bleed up to about 25,000 ft and rely on engine bleed or other sources above that. The options reflect that: 30,000 ft would exceed the usual limit, while 15,000 ft and 20,000 ft are below the maximum. Therefore, the maximum altitude for APU bleed air in flight is 25,000 ft.