Bleed air extraction from the APU is not permitted above what altitude?

Bleed air extraction from the APU is not permitted above what altitude?

• A. 15,000 Feet
• B. 25,000 Feet
• C. 30,000 Feet
• D. 35,000 Feet

Answer: (B)

Bleed air from the APU is limited by how much pressure the APU’s compressor can reliably generate at a given ambient air condition. As you climb, the surrounding air gets thinner, and the APU can’t maintain the required bleed air pressure to feed the packs and other pneumatic systems beyond a certain point. To keep essential systems powered and to avoid overloading the APU, this bleed source is not permitted above a specific altitude. That ceiling is 25,000 feet, so the APU bleed can be used up to that level but not above it. Up at cruise altitudes, engine bleed air is used instead to supply the pneumatic needs.

Bleed air from the APU is limited by how much pressure the APU’s compressor can reliably generate at a given ambient air condition. As you climb, the surrounding air gets thinner, and the APU can’t maintain the required bleed air pressure to feed the packs and other pneumatic systems beyond a certain point. To keep essential systems powered and to avoid overloading the APU, this bleed source is not permitted above a specific altitude. That ceiling is 25,000 feet, so the APU bleed can be used up to that level but not above it. Up at cruise altitudes, engine bleed air is used instead to supply the pneumatic needs.