To accomplish APU engine cooling before shutdown when necessary, one method is to

To accomplish APU engine cooling before shutdown when necessary, one method is to

• A. Open the bleed air valve
• B. Close the bleed air valve
• C. Restrict fuel supply
• D. Increase compressor speed

Answer: (B)

Cooling the APU before shutdown is achieved by reducing the thermal load on the unit. The bleed air valve controls how much hot air the APU compressor sends into the aircraft’s bleed-air system. By closing this valve, you isolate the APU from that bleed-air demand, so the APU isn’t supplying hot bleed air to the system as it winds down. This allows the engine to shed its heat more effectively through its exhaust and cooling paths, helping it reach a safer, cooler state before shutdown. Opening the valve would keep the bleed-air load on the APU, making cooling harder. Restricting fuel or cranking up compressor speed would either cause an abrupt shutdown or add more heat, not promote cooling.

Cooling the APU before shutdown is achieved by reducing the thermal load on the unit. The bleed air valve controls how much hot air the APU compressor sends into the aircraft’s bleed-air system. By closing this valve, you isolate the APU from that bleed-air demand, so the APU isn’t supplying hot bleed air to the system as it winds down. This allows the engine to shed its heat more effectively through its exhaust and cooling paths, helping it reach a safer, cooler state before shutdown. Opening the valve would keep the bleed-air load on the APU, making cooling harder. Restricting fuel or cranking up compressor speed would either cause an abrupt shutdown or add more heat, not promote cooling.