Ask the Captain: How is fresh air delivered to the airplane cabin?

Question: What does it take to get fresh air delivered into the cabin during flight?

– Jim, Thailand

Answer: In most airliners, air is compressed by the engines, cooled by the air conditioning system and then sent to the cabin. Fresh air can also be routed to the cabin from a small jet engine in the back of the airplane, known as an auxiliary power unit, or via a hose when at the gate.

Question: When your flight is delayed and you have to wait on the runway for hours, why is the air conditioning not used? I was in this predicament at LAX and it was awful. Very hot inside the aircraft.

– Doug, Panglao, Philippines

Answer: When waiting for departure it is common to shut down the engines to save fuel. The auxiliary power unit supplies electricity and air for air conditioning. Some APUs do not provide as much air, causing it to be hot and stuffy onboard.

The air conditioning system is being used but is not as effective as when engine air is used. The flight attendants can let the pilots know of any issues in the cabin, so talk to them.

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