Why do airplanes turn off the AC during takeoff?

Have you ever wondered what it would be like flying in an airplane without air conditioning? That's unimaginable and almost no one boards their flight thinking they are going to be locked in a hot cylindrical can. But every time the flight takes off, the AC turns off, only to be turned on again when the plane reaches a certain altitude. 

Why does the AC in an airlplane turns off during takeoff?

On some flights, you will notice that the AC is running when you board the plane. You are busy adjusting the ventilator placed above your head. The airflow is almost never perfect to your liking. But then the AC sometimes switches off as the plane prepares for takeoff. 

• Sometimes, it comes as a relief from being constantly blasted with cool air above your head. Other times you might be left wondering why the airflow was cut off.
• Well, it's standard policy to turn off any unnecessary power-using device during takeoff, and air conditioning in most aircraft uses power from the engines. 
• The climate control systems are turned off to ensure that engines function at full throttle on takeoff and that all power needed is left for the engines. 
• The AC is turned on after the flight reaches a safe altitude. 
• Usually, engines on some planes use bleed air (compressed air) from the auxiliary power unit for power. The same bleed air is used for air conditioning while on the ground when there are no engines running. 
• Another reason could be that air conditioning is supplied from the ground air and it is disconnected just before the door is closed. 

• In other cases where a flight is potentially delayed, pilots can choose to turn off the AC and the engines both to conserve fuel. Otherwise, the plane may have to return to the gate for refuelling.

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Flying hot!

Dimming lights and turning off AC during takeoff and even landing doesn't signal anything is wrong. However, there have been times when the AC conked off during a flight and passengers were stuck in a hot cylinder in the air with no other option. 

In October 2021, passengers on a Pune-Delhi Air India flight were left sweating and fanning themselves in what was their worst flight ever after the auxiliary malfunctioned shortly after takeoff. Then, there have been several cases where passengers were locked up inside a delayed flight on the ground with the AC turned off for several hours. 

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