If the APU is supplying bleed air or one pack fails, which airflow is delivered regardless of the PACK FLOW selector position?

When the APU is supplying bleed air or when there is a failure of one pack, the airflow delivered is automatically set to high. This is a safety and performance feature of the aircraft to ensure that sufficient airflow is maintained in the cabin for passenger comfort and to support the systems that depend on proper temperature and pressure controls.

The PACK FLOW selector typically allows crew members to choose the desired airflow setting, but in cases where there are operational constraints, such as when the APU is the primary bleed air source or one of the packs is inoperative, the system defaults to high airflow. This priority is to protect the aircraft and ensure that adequate ventilation is always available, regardless of the manual settings selected by the crew.

In normal operations, the PACK FLOW selector can be manipulated to provide the appropriate airflow, but under the discussed conditions, the system defaults to high airflow to ensure safety and performance standards are met.