Is that what it is?...250 turns of the trim wheel from stop to stop? That info wasn't available anywhere in the AMM, the FCOM or even the FCTM. Like some, I wondered how many turns it was, so thanks.
The full range (from the AMM) of the stab is 17°. This range is not available to all controls, (electric, manual, wheel), as noted in this thread, but let us assume the available range is -1 AND to 16 ANU using the big wheel.
Now we can calculate turns and degrees of trim, (remembering the comments on the difficulty of turning the wheel under some circumstances).
250 turns / 17 degrees = 14.7 turns per degree, or,
17 degrees / 250 turns = 0.07° per turn.
If the thinking and the math is correct, we can see that there is a lot of work and time to manually modify the stab trim using the wheel. In fact, those who fly/flew the B727/B737 will recall just how fast the wheel goes around when electrically-trimming in normal flight, flaps-up; the white mark on the wheel is almost a blur...
PJ2
having done manual trim on 707-737:-800 during sim training and air test over thirty years - a few points
1 stop wheel turning before you get way out of trim is the drill. But you have to notice. I note in the video posted here it took 10 seconds to disable STAB. Lion air struggled for 10 ?? minutes. In other words STAB is off so quickly that all these situations we speak of here don’t occur. And if they do, go to next step >>
2 old trick as mentioned earlier- off load stab by releasing back pressure for a few seconds allows you to trim ANU in any load situation . Both pilots both wheels with handles extended. Very quick. It’s the elevator loads against the STAB jackscrew that causes the high loads . But you have to know this and I think it’s not taught any more.
3 Stab is three times more powerful than elevators - they don’t ‘blow back’- just not designed to overcome STAB.
4 if you’ve turned off STAB ELECTRICS you can turn them on to enable ANU trim. Thumb switches. Then when back in green range - safe range- STAB OFF and trim manually.
5 But- and this all gets back to training- you have to know all this. Not look in manuals. It has to be in the core of your airplane skill base. Trained by the trainers. And if the trainers don’t have it ........
Summary. Are pilots new to 737 aware of the dangers posed by the stabiliser?
They do runaway stab, jammed stab and manual reversion during type rating training- at least did until recently! So they know how tough an animal the STAN can be but manageable.
MCAS
So. MCAS being sorted. Good thing. Does that leave us still with a much bigger problem? The elephant in the room! What’s going to happen next time an automated function badly misbehaves- and it will.
Y