B-737 Elec Trim Switch

[Gominder]

Itīs just a point...
The trim switch located on the control wheel is actually a pair of two switches. For a trim input you have to push both of them.
With either autopilot engaged, you can disengage the a/p by giving a trim input.
So far so good...
But hitting only the right half of the switch...nothing will happen, the a/p stays engaged. Hitting the left half of the switch disengages the a/p. Or was it the other way around ???
Is there any technical background?

Have fun on trying it on your 737...itīs a easy way to win your beer for your after landing party.

[critcaact]

Gominder,
Small point.
Engaging electric pitch trim only disengages autopilot pitch mode.

[Cornish Jack]

I don't 'do' 737 but I imagine that the system is the same as the '47 etc. which is that for each trim axis there is a requirement for TWO inputs in order to activate the trim - one ARMING signal and one DIRECTIONAL command; hence the two switches. The switch which doesn't trip the A/P is the arming signal the one which does is the directional signal.
Same for aileron and rudder - the aileron one makes a good party trick... move them in opposite directions and the trim will operate as per the directional switch.... on the 47/4 the rear aileron switch of the pair is the directional one.

[static]

critcaact,

Hitting the trim switch totally disengages the autopilot on 737-300 to -900.

[OneDotLow]

Am I not correct I saying that one switch is for the motor, and the other for the 'clutch'?

ODL

[Cough]

Cornish - Almost right, arming does, direction doesn't! (Played with it on the ground on Sat)

CCCccc....ough

[Cornish Jack]

Whoops!!
Thanks Cough - as 'they' say ..."Never assume, check!!"

[Few Cloudy]

One Dot Low,

If by clutch you mean brake, as in Douglas, the brake does not get taken off electrically on the B737, but is overridden mechanically, whenever the trim wheel rotates.

[TexasFlyer]

Interesting, I have a Mooney and it has two switches which do exactly as described prev on the 737, must be an FAA standard. Mine doesn't go woop woop when you disengage - it goes beeeeeeeeep.