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The warning above the big white switches in the following picture had me intrigued. Is there some FAA regulation related to the same?

WARNING: Airconditioner must be off to insure normal takeoff climb performance

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    $\begingroup$ That placard is one way of handling CRM... $\endgroup$ – FreeMan Oct 22 '15 at 15:12
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    $\begingroup$ Evidently it's a Piper Archer. $\endgroup$ – fooot Oct 22 '15 at 15:42
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    $\begingroup$ AC sucks power out of the engines, just like in a car. $\endgroup$ – Tyler Durden Oct 22 '15 at 17:05
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    $\begingroup$ The power loss from AC is worse when you misspell the word "ensure". $\endgroup$ – Daniel Griscom Oct 23 '15 at 1:48
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    $\begingroup$ @erdekhayser This is a GA airplane, not an airliner. It's a single crew aircraft and the "co-pilot" would usually be a passenger (or a flight instructor...) $\endgroup$ – reirab Oct 23 '15 at 4:35
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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.

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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.

In specific regards to the Piper Archer (pictured here) the POH states

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.

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  • $\begingroup$ The same is true for landing, in case a go around would be required. $\endgroup$ – mins Oct 22 '15 at 20:05
  • $\begingroup$ I'm pretty sure I remember seeing a similar statement in the POH for the Cherokees with A/C, too (not that the ones I've flown actually had A/C...) $\endgroup$ – reirab Oct 23 '15 at 4:38

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