If all four overpressure shutoff valves close while airborne, what systems will be lost?

When all four overpressure shutoff valves close while the aircraft is airborne, it results in the loss of both the air conditioning system and the ice protection system. The overpressure shutoff valves are critical for controlling the airflow and maintaining the required pressure within these systems.

The air conditioning system is responsible for providing a comfortable environment in the cockpit and cabin, regulating temperature, and managing humidity levels. When the overpressure shutoff valves close, the airflow necessary for the air conditioning system is interrupted, leading to a failure in climate control.

Simultaneously, the ice protection system, which prevents ice formation on critical surfaces of the aircraft, also relies on this airflow. The closure of the overpressure shutoff valves disrupts the operation of the ice protection system, increasing the risk of ice build-up that can adversely affect aircraft performance and safety.

Therefore, the correct answer identifies the loss of both the air conditioning and the ice protection systems as a direct consequence of the overpressure shutoff valves being closed during flight.