When does bleed air switching occur during landing?

• A. When approach mode is engaged.
• B. Only after touchdown.
• C. Flaps greater than 20 degrees or the landing gear is down.
• D. At go-around command.

Answer: (C)

Bleed air switching is tied to the airplane’s landing configuration. As you move into approach and landing, the system recognizes that flaps are extended (typically more than 20 degrees) or the landing gear is down, and it changes the bleed air source accordingly. This ensures a steady, sufficient supply of bleed air for cabin conditioning and avionics needs without relying on engine bleed when the engines are operating at idle, or when engine bleed may be needed for anti-ice or other critical functions during the final phase of flight. In short, the switch is triggered by the aircraft entering landing configuration, not by merely engaging approach mode, nor by touchdown or a go-around command.