Up to what altitude can the APU bleed be used to supply bleed air?

Up to what altitude can the APU bleed be used to supply bleed air?

• A. 15,000 feet MSL.
• B. 5,000 feet MSL.
• C. 25,000 feet MSL.
• D. 30,000 feet MSL.

Answer: (A)

Bleed air for the environmental control system must come from a source capable of delivering the required mass flow and pressure. The APU’s bleed capability is limited by altitude because the compressor can’t maintain the needed pressure at higher air densities. Up to fifteen thousand feet above mean sea level, the APU can still provide the required bleed air to feed the packs and support cabin conditioning and pressurization. Beyond that altitude, the APU can no longer sustain adequate bleed air, so engine bleed air (or another source) must be used to keep the packs operating.

Bleed air for the environmental control system must come from a source capable of delivering the required mass flow and pressure. The APU’s bleed capability is limited by altitude because the compressor can’t maintain the needed pressure at higher air densities. Up to fifteen thousand feet above mean sea level, the APU can still provide the required bleed air to feed the packs and support cabin conditioning and pressurization. Beyond that altitude, the APU can no longer sustain adequate bleed air, so engine bleed air (or another source) must be used to keep the packs operating.