Why Airplanes turn off the AC before takeoff

Have you ever noticed that the cabin feels warmer just before a plane takes off?

Many passengers wonder why the air conditioning seems to stop working at that moment. The reason is not a technical problem it is part of the aircraft’s normal operating procedure.

When passengers board the plane the cabin is usually cooled by an external air conditioning system at the airport.

This keeps everyone comfortable while the aircraft is parked at the gate.

Just before departure the external power and cooling supply are disconnected.  At that point the aircraft switches to its Auxiliary Power Unit (APU) a small onboard engine that provides electricity and cool air until the main engines are fully running.

During takeoff pilots need as much engine power as possible to safely lift the aircraft into the air.  To help achieve this some systems that are not essential during takeoff including parts of the air conditioning and climate control system may be temporarily reduced or switched off.

This allows more engine power to be used for takeoff instead of running cabin cooling systems.

Former American pilot John Cox explains that this short changeover happens because the aircraft moves from ground power to its own power systems.

Once the engines are operating normally and the plane reaches a stable stage of flight the air conditioning returns to normal and the cabin quickly becomes comfortable again.

So, if the cabin feels a little warm before takeoff there is usually no reason to worry. It is a normal part of the flight process designed to support a safe and efficient departure.