When the BLEED VALVE selector is in AUTO with the anti-ice off, what is the bleed air source on the ground and in flight, respectively?

When the BLEED VALVE selector is set to AUTO and the anti-ice system is off, the bleed air source operates differently on the ground and in flight due to the specific requirements and safety considerations associated with vehicle operation in those environments.

On the ground, the bleed air source is sourced from the Auxiliary Power Unit (APU). The APU is used while on the ground to provide bleed air for air conditioning and other systems without needing to run the engines. This setup helps to conserve fuel and minimizes engine wear, allowing the aircraft to operate its environmental control systems efficiently.

In flight, once the engines are running and generating sufficient power and bleed air for operational needs, the source switches to the engines. The engines provide the necessary bleed air for various systems as they are more efficient than the APU once the aircraft is airborne.

Understanding this operational strategy reinforces how the aircraft manages its systems effectively, ensuring that the most efficient and safest power sources are used depending on the phase of flight.