Stab trim fix question?

[pandy2806 0]

Hi, I couldn't help but notice that when I was on the ground with all the hydraulic pumps turned off I was still able to adjust the trims as if I had full hydraulic power?! I'm no expert on the 737 NG, but I always thought that to use the stab trim you needed to have at least one hydraulic system pressurised?! I do know that this is indeed the case on the 747-400 as I have a lot of sim experience on the type, including being a pilot for UK Worldflight for the past 4 years. Surely with a tailplane the size of the 737's it would need power to move it?

[Spin737 102]

The only pumps you need are electron or blood. No hydraulics involved in the stab trim.And don't call me Shirley.

[ajacied551 1]

You dont,t need hydraulic power to move the stabilizer, The stabilizer trim system is the only flight control system on the 737 that don't have hydraulic power to move stabilizer. This system have a electrical actuator that drive's stabilizer up and down with stabilizer trim switch on the capt and F/O Control wheel's, or by the autoflight system.The Stabilizer trim actuator moves a stabilizer gearbox, When the stabilizer gearbox moves, It moves the jackscrew that moves the stabilizer up and down, The gearbox also back drives the stabilizer aft and forward cable drums. Movement of the forward cable drum moves the manual trim wheels and stabilizer indicator pointer. You can also use the stabilizer trim wheel's to move the stabilzer manually.

[pete_auau 1,153]

Hi, I couldn't help but notice that when I was on the ground with all the hydraulic pumps turned off I was still able to adjust the trims as if I had full hydraulic power?! I'm no expert on the 737 NG, but I always thought that to use the stab trim you needed to have at least one hydraulic system pressurised?! I do know that this is indeed the case on the 747-400 as I have a lot of sim experience on the type, including being a pilot for UK Worldflight for the past 4 years. Surely with a tailplane the size of the 737's it would need power to move it?

thought being a pilot u would have known this

[pandy2806 0]

No of course I didn't know this otherwise I wouldn't have asked this question. Like I said I'm not a real pilot, but most of my simming experience is on the 747 which does require hydraulics to work the trim. I was just wrongly assuming that was the same in the 737 obviously as it moves the whole tailplane as does the 744. If it's electric it must require some decent power then?! :)

[Spin737 102]

If it's electric it must require some decent power then?! :)

It's electric or manual. You can crank it by hand. On the trim wheel, there are pop-out handles in case you need them (eg. during de-ice operations).