737 Trim Air
 

We never turn trim air off on our 737s that have trim air. I was told that AA turns off trim air in the ground. And recently I saw a photo of a Ryan Air 737 and they had their trim air off. Can someone enlighten me as to why one would not use trim air?

The 737-800’s have had a lot of trim air faults in the early days. There is a Boeing FCOM Bulletin titled “Nuisance Zone Temp Light Illuminations on 737-800 Airplanes.” The procedure is as follows:

After landing, prior to first power transfer:
Trim Air Switch ……………………………………….. OFF
Air Conditioning System ……… ____Pack(s), BLEEDS ON

Prior to takeoff, after last power transfer:
Trim Air Switch ………………………………………….. ON

We follow the above procedure as well on our 800s

Thanks. Sounds like a legacy procedure that is not valid today. I've never had a zone temp light in an -800 or -900. I remember, maybe 2 in the -400 when we first got them. Still, if the cabin temp was somehow more stable or easier to control, I'd like to try it.

Procedures that have no basis in reality or are unnecessary annoy me.

True, Mike. The Trim Air switch was incredibly dusty in all the jets I flew.