Cabin Air

[Genesis]

A fellow member suggested I ask my question here...


So I understand how when an airplane is running fresh air is constantly being pulled in and delivered to the cabin via the air conditioner. But when the pilot(s) turn off the engines, say when waiting at the gate, sitting on the runway/tarmac, etc. with the door closed, how do the passengers get fresh air to breathe? How is it that people don't suffocate or pass out from a lack of air while sitting for hours?

[Captain Hutch]

Good question! When sitting on the ground with the engines not running at the gate, power can be supplied to the aircraft by an external power unit connected to the aircraft or the aircraft's own internal Auxiliary Power Unit (APU). The APU is a little jet engine usually located somewhere in the tail section of the aircraft. Air Conditioning can also be supplied by an external air conditioner at the gate. Away from the gate, the APU provides both functions, air and electrical. The air conditioner can pull air through the ram air door via a turbofan or a recirculation fan can take the existing cabin air through a filter back into the cabin or a combination of both. The ram air door is a louvered opening usually located somewhere near where the wing connects to the fuselage. In high speed flight it doesn't need to be open very much to allow the proper amount of airflow thru the cabin, but on the ground and in slower phases of flight, such as configured for landing, the ram air door is fully open. There is a discharge valve too to help control the amount of air exiting the aircraft.

This is the general configuration for a B737 and the details vary from model to model, and I'm guessing the system is approximately the same for most airliners.

I hope that helps! :tiphat:

Hutch