The warning above the big white switches in the following picture had me intrigued. Is there some FAA regulation related to the same?
It is not an FAA regulation to have the air conditioning off during takeoff and/or landing, however some manufacturers require it, in which case the pilot is legally obligated to comply with it.
I have flown two aircraft (both jets) which required it to be off:
- Some of the Learjets require the AC to be off for both takeoff and landing because it uses a high draw electrical motor to drive the compressor, and when it cycles off and on it causes electrical spikes which can cause problems with the anti-skid system.
- Some of the Dassault Falcon jets require the AC to be off for takeoff (actually, they automatically turn it off, but if the automatic system is inoperative the MEL requires turning it off manually) for performance reasons. Since the AC is these aircraft is using bleed air off of the engine compressor as a source, allowing the air to continue through the engine instead increases thrust.
I know that many airliners have the option to takeoff with it on or off for performance reasons, and provide performance charts or adjustments for both.
As far as I know there is no specific regulation covering Air Conditioner operation however this varies from aircraft to aircraft and you should always check your specific aircrafts POH for information on systems installed and how they are to be operated.
On air conditioned models, the air conditioner must be “OFF” to ensure normal takeoff performance.
In terms of why that is there, Air Conditioner units use engine power to run (they are basically heat pumps). In smaller aircraft, especially on the slower/low power end of the spectrum (like the archer pictured here) taking away HP to run an AC unit can mean the difference between clearing a 50ft obstacle and not clearing it.
As for FAA regulations, the FAA does outline procedures for certifying a plane for reduced thrust takeoffs, however this involves power setting alterations. Depending on how you look at it running the Air Conditioner is in a way a reduced power takeoff however since you cant specifically adjust Air Conditioner power draw (as far as I know) running it could draw an unknown and potentially variant amount of power.