During single engine operations, what is the maximum altitude the APU may be started?

During single engine operations, what is the maximum altitude the APU may be started?

• A. 10,000 ft MSL
• B. 15,000 ft MSL
• C. 20,000 ft MSL
• D. 25,000 ft MSL

Answer: (B)

During single-engine operations, the APU is used to provide bleed air and electrical power so you can start the remaining engine and power essential systems without relying on the operating engine. The APU has a flight-start altitude limit, and it can be started in flight up to 15,000 ft MSL. This limit exists because, at higher altitudes, ambient pressure and air density reduce the APU’s ability to deliver sufficient bleed air for a reliable engine start and to meet system needs. Therefore, the maximum altitude to start the APU in this scenario is 15,000 ft MSL.

During single-engine operations, the APU is used to provide bleed air and electrical power so you can start the remaining engine and power essential systems without relying on the operating engine. The APU has a flight-start altitude limit, and it can be started in flight up to 15,000 ft MSL. This limit exists because, at higher altitudes, ambient pressure and air density reduce the APU’s ability to deliver sufficient bleed air for a reliable engine start and to meet system needs. Therefore, the maximum altitude to start the APU in this scenario is 15,000 ft MSL.