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737 Stuck Manual Trim Technique

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737 Stuck Manual Trim Technique

Old 5th Apr 2019, 12:04
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737 Stuck Manual Trim Technique

Inability to operate the manual trim on a 737 is a hot topic just now.

During my 737 type conversion (3-400 series, UK, 1998) we were shown a techniqe for trimming manually even when aerodynamic loads were too large to allow normal movement of the wheel.

A large out-of trim input was provided and an attempt to turn the wheel manually proved it to be immovable. Recovery was for both pilots to pull the column back to give an appreciable pitch up, if only a few degrees, and then relax the pull. The resulting controlled pitch down released enough load on the stab to allow a bit of trim - perhaps less than half a turn initially, to be achieved. The procedure was repeated and with each repetition more and more manual trim was achieveable until a point was reached where normal though very stiff operation became possible.

I seem to recall this was a demonstration that manual trim remained available even in out of trim conditions way beyond those anticipated even in the worst concieveable runaway.

Is this a standard part of 737 conversions or was it an add-on by our very punctilious trainer? I'd be most interested to know how widely this technique is known because once seen, it would never be forgotten. I suspect the Ethiopian pilots hadn't seen this or there would be signs of pulls and bunts on the data, and possibly no acident to discuss either.

737 pilots - over to you....

Last edited by meleagertoo; 5th Apr 2019 at 12:22.
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Old 5th Apr 2019, 12:31
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Covered here:
Boeing advice on "aerodynamically relieving airloads" using manual stabilizer trim

I suspect the Ethiopian pilots hadn't seen this or there would be signs of pulls and bunts on the data, and possibly no acident to discuss either.
It appears they couldn't stop the aeroplane flying into the ground, let alone get the nose high enough to do that...
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Old 5th Apr 2019, 13:03
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fdr
 
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Originally Posted by meleagertoo View Post
Inability to operate the manual trim on a 737 is a hot topic just now.

During my 737 type conversion (3-400 series, UK, 1998) we were shown a techniqe for trimming manually even when aerodynamic loads were too large to allow normal movement of the wheel.

A large out-of trim input was provided and an attempt to turn the wheel manually proved it to be immovable. Recovery was for both pilots to pull the column back to give an appreciable pitch up, if only a few degrees, and then relax the pull. The resulting controlled pitch down released enough load on the stab to allow a bit of trim - perhaps less than half a turn initially, to be achieved. The procedure was repeated and with each repetition more and more manual trim was achieveable until a point was reached where normal though very stiff operation became possible.

I seem to recall this was a demonstration that manual trim remained available even in out of trim conditions way beyond those anticipated even in the worst concieveable runaway.

Is this a standard part of 737 conversions or was it an add-on by our very punctilious trainer? I'd be most interested to know how widely this technique is known because once seen, it would never be forgotten. I suspect the Ethiopian pilots hadn't seen this or there would be signs of pulls and bunts on the data, and possibly no acident to discuss either.

737 pilots - over to you....
The wording in the FCTM, P 8.17 is rather different to the technique discussed, the nicest thing that can be said is that it is understated and leaves a great deal to the imagination. It may just be that we are all separated by a common language, but being kind, perhaps the FCTM leaves a great deal to the creativity of the TCI/TRI etc. The technique is great sport, not so sure it adds confidence in the strength provided by certification standards. Conceptually, both pilots needed on the controls to deal with a fault that is not impossible to occur seems to be untidy at best. Expecting the crew to undertake aerobatics without having a tail wheel and another set of wings over the top painted in chequers seems to be out of place. There is a silver lining however, that is that the operators should be able to charge more for the disneyland ride that is considered to be appropriate.

If a runaway trim event was about as remote as me winning the lottery, there wouldn't be a problem, it would be hypothetical, and the matter would be just a curious gedankenexperiment, but the recent events suggest it is not, and the 50 years that this has been accepted as a solution may speak loudly to the state of the art. Had Orville suggested to Lt Selfridge that one of the plans of recovery was to follow the wright flyers FCTM in such a manner, the selfless Lt would have probably stayed landside, after all, that was before the time of airline coffee, pretzels and peanuts being served airborne.

FAA Part 142, manual trim use, Yes, manual trim use post stabiliser runaway, No. Yo-yo? Nope. Jack stall from military training only.

Last edited by fdr; 5th Apr 2019 at 14:21.
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Old 5th Apr 2019, 13:10
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If the trim cannot be brought to within operating range quickly enough, the next option is to roll the plane to invert it - after turning the seat belt signs on.
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Old 5th Apr 2019, 13:23
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Pity, I thought I'd asked a straightforward question, I'll try again.

How many have and have not seen this demonstrated in the sim?
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Old 5th Apr 2019, 14:51
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First bring the power back.... 94% power with the nose down will make it impossible to use manual trim, for unreliable airspeed 4deg nose up and 80% power will give you strait and level with flaps out 10deg/75%
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Old 5th Apr 2019, 15:26
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meleagertoo, long time ago but yes i have used that technique. Not exactly taught it at the time but you were supposed to know about "unloading" the airframe. If I remember correctly it was really the only way to get the trim moving manually with the stab run to full down, without rupturing yourself.(737-300)
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Old 5th Apr 2019, 15:32
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What are the flap limiting speeds..? Does the MCAS operate when the flaps are `UP`,or When the flap lever is moved to the `UP` POSITION...?
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Old 5th Apr 2019, 16:37
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..and Boeing expects to carry passengers in these wretched things?

Last edited by BEagle; 5th Apr 2019 at 19:15.
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Old 5th Apr 2019, 22:04
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Originally Posted by bzh View Post
First bring the power back.... 94% power with the nose down will make it impossible to use manual trim, for unreliable airspeed 4deg nose up and 80% power will give you strait and level with flaps out 10deg/75%
Well, your premise is ok, but your figures are not. Boeing's memory items are 4deg/75% (flaps up) and 10deg/80% (flaps extended).

And that won't give you level flight, it will give you a speed not below minimum, not above maximum, at any weight, and will give you a climb at low level and a descent at high level. In other words, it will give you safe flight without reference to other instruments.

For the OP, no, I've never been trained an unloading technique in the simulator. I've only read about it in my spare time.
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Old 6th Apr 2019, 05:16
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We used to practice manual trimming in the
B727 during sim sessions

Required coordination by both pilots and the loads were significant but it was doable


Only once used it in real life after de-icing the stab froze up in cruise but soon freed up
as we descended into warmer air
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Old 6th Apr 2019, 07:20
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Too much speed can spoil your chances in an unreliable airspeed or 'stab out of position' upset.

But what to do in that first second just after you recognise that you have a problem?

On my last type, a factory pilot told me that the manufacturer designed it in such a way, that if you just put the N1 needles at 12 O'clock, you'll neither go too fast or too slow to get in trouble.

This was on an Embraer, but is there a similar 'rough guide' for the Boeing?
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Old 6th Apr 2019, 07:27
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But what to do in that first second just after you recognise that you have a problem?

On my last type, a factory pilot told me that the manufacturer designed it in such a way, that if you just put the N1 needles at 12 O'clock, you'll neither go too fast or too slow to get in trouble.

This was on an Embraer, but is there a similar 'rough guide' for the Boeing?
For a UAS, you would do the UAS memory items, which include a pitch attitude and an N1, as pointed out by Derfred in his post above.

Last edited by Capn Bloggs; 6th Apr 2019 at 11:07.
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Old 6th Apr 2019, 08:50
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Unhappy

Originally Posted by meleagertoo View Post
Inability to operate the manual trim on a 737 is a hot topic just now.

During my 737 type conversion (3-400 series, UK, 1998) we were shown a techniqe for trimming manually even when aerodynamic loads were too large to allow normal movement of the wheel.

A large out-of trim input was provided and an attempt to turn the wheel manually proved it to be immovable. Recovery was for both pilots to pull the column back to give an appreciable pitch up, if only a few degrees, and then relax the pull. The resulting controlled pitch down released enough load on the stab to allow a bit of trim - perhaps less than half a turn initially, to be achieved. The procedure was repeated and with each repetition more and more manual trim was achieveable until a point was reached where normal though very stiff operation became possible.

I seem to recall this was a demonstration that manual trim remained available even in out of trim conditions way beyond those anticipated even in the worst concieveable runaway.

Is this a standard part of 737 conversions or was it an add-on by our very punctilious trainer? I'd be most interested to know how widely this technique is known because once seen, it would never be forgotten. I suspect the Ethiopian pilots hadn't seen this or there would be signs of pulls and bunts on the data, and possibly no acident to discuss either.

737 pilots - over to you....
What you discribe is Pilot training, thats not done any more...

These days we train operators!

They get airborne with a minor sensor fault and instead of identfying the nature of the failure unverstandig it and flying the aircraft (pitch/power) they operate as usual A/P On, LNAV, flaps up turning HDG bugs talking to ATC etc.
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Old 6th Apr 2019, 09:25
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Originally Posted by KRH270/12 View Post


What you discribe is Pilot training, thats not done any more...

These days we train operators!

They get airborne with a minor sensor fault and instead of identfying the nature of the failure unverstandig it and flying the aircraft (pitch/power) they operate as usual A/P On, LNAV, flaps up turning HDG bugs talking to ATC etc.

What is described is also a design that is not compliant with the requirements of Part 25. There is no justification that can be made that an aircraft needs to be handled in such a manner with the failure of a system that is both possible and part of the design requirement to have no adverse effects on failure... Forget about MCAS, how on earth is the procedure in the FCTM reasonable or acceptable. This is not an acro, it is a transport category aircraft.
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Old 6th Apr 2019, 09:44
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how on earth is the procedure in the FCTM reasonable or acceptable.
If done properly and no doubt Boeing's test pilots did measured tests, then if it saves your life then it's acceptable..Competence as a pilot is preferable of course. But evidence suggests all pilots are not necessarily competent.
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Old 6th Apr 2019, 09:58
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Originally Posted by KRH270/12 View Post


What you discribe is Pilot training, thats not done any more...

These days we train operators!

They get airborne with a minor sensor fault and instead of identfying the nature of the failure unverstandig it and flying the aircraft (pitch/power) they operate as usual A/P On, LNAV, flaps up turning HDG bugs talking to ATC etc.
AFAIK checklists were introduced to standardise training, and avoid risky seat-of-the-pants flying. Pitch and power is rarely part of standard flying. Unfortunately those checklists don't cover multiple simultaneous warnings, let alone the underlying AOA faults. Ironically, a very short AOA disagree checklist would have helped a lot, but this output was not even included as standard on the flight display. Instead the pilots had to fall back on several half-baked checklists, emergency ADs, and intuitive diagnosis.
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Old 6th Apr 2019, 11:03
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Thanks Bloggs.

So what N1 do you set on Boeing then?
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Old 6th Apr 2019, 11:04
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Exclamation

Originally Posted by GordonR_Cape View Post
AFAIK checklists were introduced to standardise training, and avoid risky seat-of-the-pants flying. Pitch and power is rarely part of standard flying. Unfortunately those checklists don't cover multiple simultaneous warnings, let alone the underlying AOA faults. Ironically, a very short AOA disagree checklist would have helped a lot, but this output was not even included as standard on the flight display. Instead the pilots had to fall back on several half-baked checklists, emergency ADs, and intuitive diagnosis.
No its not, i got. about 13k h on the 737 and all the hefty non normals start like this -> A/P OFF, A/T OFF

and then??? Its good old pitch and power, thats not Seat-of-the-pants-flying, its basic flying Skills that are required.

its pitch and power that keeps you airborne...

I agree with you that Boeing messed this one up big time. And i am not blaming the Crew here.

But when most big non normals like engine failures, windshear, runaway stab., TCAS RA, EGPWS warnings, stall recovery require manual flight manual throttle.... you better have well trained pilots on that flight deck rather then minimum trained operators....
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Old 6th Apr 2019, 11:10
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Originally Posted by Nomad2
So what N1 do you set on Boeing then?
:
Originally Posted by Derfred in post 10
Well, your premise is ok, but your figures are not. Boeing's memory items are 4deg/75% (flaps up) and 10deg/80% (flaps extended).
In mine, it's 80% in both cases, same deck angle.
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