I know that some of the Boeing planes have the two levers which look like speed brake handles that are labeled STAB TRIM.
To those who fly these birds, what is it like using those? I know that most of the time you would use the thumb switches, and that on later versions the levers are replaced with dual switches, but in the event that you use them do you just pull them both back a bit or push forward as needed?

 

They provide an increased range of stab trim travel which is sometimes used to set takeoff trim with aft cg conditions. The signal also overrides or neutralizes (depending on model) any other conflicting trim inputs. Levers or switches are simple push-pull operation, spring loaded to neutral position.

 

Ah, spring loaded, I see now... thanks. Just looking at them I'd assumed that if you pulled it to a certain position that it would stay there. Good to know.

 

As I recall, one lever/switch releases the stab trim brake and the other actuates the trim motor. If the thumb switches fail, the spring-loaded console levers bypass that circuit and go directly to the two actuators.

 

For the B747-400:

The control wheel trim switches must be moved together. This signals both trim control modules, through the Normal electrical channels, to position the stab with both trim actuators.

Autopilot trim uses the same normal electrical channels as control wheel trim. However, the autopilot can only use one channel, the left or right depending on autopilot selected. This is why the autopilot trims at "1/2 rate".

Since both control wheel trim switches and autopilot trim use the same electrical channels, if the autopilot is engaged and the control wheel switches are actuated, the autopilot disengages. If multiple autopilots are engaged, then control wheel trim is inhibited.

What you are referring to are the Alternate Trim switches.

The Alternate Stabilizer Trim switches provide trim commands in the same manner as the Stabilizer Trim switches through separate control channels.

They provide increased trim range and since ALTN Trim uses a separate control channel, it will override autopilot trim regardless of which autopilot(s) are engaged.

The ALTN trim will not disengage the autopilot.

 

Awesome explanation cougar, that's why I love the Tech forum... so much better than the dredge over in the Regional forum!
My biggest shock is that the levers are spring loaded to neutral... always assumed they'd stay where you moved them.

 

Now can we talk about how to roll the trim wheel on the 727 when you hand fly it to altitude and want to level off and accelerate?

https://www.google.com/search?hl=en&...ml%3B448%3B336

;^)

 

Stow the hand crank, your knees will thank you.

 

Push the trim wheel forward when disengaging the A/P, and the A/C won't buck. [Information lost to the ages.]

 

The first time you get hit in the knee with that handle, it WILL be the last....and damn it hurts.