737 Stuck Manual Trim Technique
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Just out of curiosity, looking at the initial report for the last minutes:
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.
How do you recover without unloading (diving) the aircraft?
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.
How do you recover without unloading (diving) the aircraft?
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Even if it was possible to manually trim in their state, the crew may not have been aware of just how much force it would take. The ops manual does not provide much guidance on this. Since the Captain presumably had all his hands full with the yoke, the FO probably tried the crank handle but either could not turn it or simply did not apply enough force.
Just out of curiosity, looking at the initial report for the last minutes:
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.
How do you recover without unloading (diving) the aircraft?
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.
How do you recover without unloading (diving) the aircraft?
Kind of sounds like it might be a certification requirement, or at least something that Boeing would have flight-tested at some stage in the last 50 years, though probably best not tried at home.
(no criticism intended or implied of the crew's decision to disable stab trim per the checklist)
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Just out of curiosity, looking at the initial report for the last minutes:
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.
How do you recover without unloading (diving) the aircraft?
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.
How do you recover without unloading (diving) the aircraft?
Edit: DaveReidUK There seems to be little clear data on the trim forces of a loaded horizontal stabiliser in that flight regime. More research may be needed, if the accident investigation justifies it.
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Trimming electric plus manual at the same time, wasn't that the reason of the Alaska Airlines crash?
https://en.wikipedia.org/wiki/Alaska...nes_Flight_261
See how much debating is going on in both threads, see how much we have learned more about the system in the last weeks.
Those poor fellas had to find a solution in just minutes with a situation that was running out of hand big time, causing confusion and CCR breakdown. I wouldn't point a finger yet at the guys up front. Most likely I'll never will.
Let's face it, I admit honestly I wouldn't like to have been in that scenario.
Although I've have never flow 737's but nearly all of the 747 versions, I wonder if I would have made the day with the right decisions.
https://en.wikipedia.org/wiki/Alaska...nes_Flight_261
See how much debating is going on in both threads, see how much we have learned more about the system in the last weeks.
Those poor fellas had to find a solution in just minutes with a situation that was running out of hand big time, causing confusion and CCR breakdown. I wouldn't point a finger yet at the guys up front. Most likely I'll never will.
Let's face it, I admit honestly I wouldn't like to have been in that scenario.
Although I've have never flow 737's but nearly all of the 747 versions, I wonder if I would have made the day with the right decisions.
What trim changes occur if you pop the speedbrakes..? Nose-up..?
Then select `flaps` to lowest setting,then retrim..?As Ibelieve the MCAS only operates when the flaps are selected `up`..?
Then select `flaps` to lowest setting,then retrim..?As Ibelieve the MCAS only operates when the flaps are selected `up`..?
Only half a speed-brake
gents, anyone able to asnwer these: https://www.pprune.org/rumours-news/619272-ethiopian-airliner-down-africa.html#post10441180
help appreciated.
How much of trim displacement in units is one spin of the manual wheel on the MAX/NG?
About the yoke elec trim thumb rocker switches
- do they control the actuators/motor directly in analogue, or only send signals to some sort of FCS logical subunit?
- what is the logic for simultaneous inputs L+/-R?
Is there an authoritative answer, whether or not the re-activation (after the 5 sec denial period) of MCAS software routine could override a live, running trim command from the elec thumb switches?
About the yoke elec trim thumb rocker switches
- do they control the actuators/motor directly in analogue, or only send signals to some sort of FCS logical subunit?
- what is the logic for simultaneous inputs L+/-R?
Is there an authoritative answer, whether or not the re-activation (after the 5 sec denial period) of MCAS software routine could override a live, running trim command from the elec thumb switches?
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gents, anyone able to asnwer these: https://www.pprune.org/showthread.php?p=10441180
help appreciated.
help appreciated.
Conversely MCAS trims down at 0.27 units per second, or 3.5 rotations of the wheel per second! That is a lot of manual winding, for every 9 second activation.
The rest will have to be officially answered by Boeing engineers.
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I would have recognized a runaway trim. Held the electric trim back until I didn't need so much control force. At the same time I'd call for the "Runaway Stab Trim" QRC/QRH. Used to be a memory item.
Both accidents used the trim to stop the motion, but NOT to reverse the trim. Anyone that hand flies the airplane much knows that you have to trim the hell out of Boeings, and trim some more. I suspect some serious training deficiencies, along with lack of experience.
I'm not buying that they could trim manually. They were doing less than 350KIAS. I suspect they didn't pull the handle out to crank it.
Both accidents used the trim to stop the motion, but NOT to reverse the trim. Anyone that hand flies the airplane much knows that you have to trim the hell out of Boeings, and trim some more. I suspect some serious training deficiencies, along with lack of experience.
I'm not buying that they could trim manually. They were doing less than 350KIAS. I suspect they didn't pull the handle out to crank it.
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What is described by the OP was taught to me (But not demonstrated ) when flying a PC6 jumpship, to defeat the classic killer of landing empty with full aft trim and forgetting to set it to half fwd for a full load take-off. Albeit a smaller plane, the PC6 has a full moving stabiliser and is subject to the same problem. This has claimed a number of lives on the dropzones.
Never heard about it on the B737 though.
Never heard about it on the B737 though.
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[QUOTE=HalinTexas;10441177
There was no reason to turn the electric trim switches back on, but since they did, they should have used it! If they had, they could have saved the airplane.
.[/QUOTE]
In my limited understanding of the B-737 MAX MCAS/trim workings, I believe that once the trim Cut Out switches are opened, the only way to trim the stabilizer is via the manual trim wheels. My friends with Boeing experience say that this is a slow and physically taxing operation. To re-trim the horizontal stabilizer quickly would require closing of the trim Cut Out switches, but, of course, that would allow the MCAS to re-initiate the nose down trim action. The pilots would have had a very small window of opportunity (maybe 5 seconds) in which to close the Cut Out Switches, trim ANU, and open the Cut Out switches before MCAS could resume commanding AND.
Just as a matter of interest, I quote from the Boeing 707 Stratoliner Flight Manual, Revision 11-8-60, entitled "Stabilizer Trim Emergency Operation":
"If the stabilizer electric trim becomes inoperative, the manual trim can be used. Due to the flight loads imposed in an out of trim condition, it may be necessary to release the control column to a low force position and retrim while in an "unloaded" condition. If the airplane is much out of trim , this action will have to be repeated until correct trim is obtained."
The manual also stated that the procedure to "Raise Nose" if the stabilizer was jammed nose down was to deactivate the inboard spoilers and raise the outboard spoilers by operating the speed brake lever.
I don't remember where or how I obtained this manual, but I've had it for 30 years or so.
Cheers,
Grog
There was no reason to turn the electric trim switches back on, but since they did, they should have used it! If they had, they could have saved the airplane.
.[/QUOTE]
In my limited understanding of the B-737 MAX MCAS/trim workings, I believe that once the trim Cut Out switches are opened, the only way to trim the stabilizer is via the manual trim wheels. My friends with Boeing experience say that this is a slow and physically taxing operation. To re-trim the horizontal stabilizer quickly would require closing of the trim Cut Out switches, but, of course, that would allow the MCAS to re-initiate the nose down trim action. The pilots would have had a very small window of opportunity (maybe 5 seconds) in which to close the Cut Out Switches, trim ANU, and open the Cut Out switches before MCAS could resume commanding AND.
Just as a matter of interest, I quote from the Boeing 707 Stratoliner Flight Manual, Revision 11-8-60, entitled "Stabilizer Trim Emergency Operation":
"If the stabilizer electric trim becomes inoperative, the manual trim can be used. Due to the flight loads imposed in an out of trim condition, it may be necessary to release the control column to a low force position and retrim while in an "unloaded" condition. If the airplane is much out of trim , this action will have to be repeated until correct trim is obtained."
The manual also stated that the procedure to "Raise Nose" if the stabilizer was jammed nose down was to deactivate the inboard spoilers and raise the outboard spoilers by operating the speed brake lever.
I don't remember where or how I obtained this manual, but I've had it for 30 years or so.
Cheers,
Grog
I did ask the question about airbrakes/speedbrakes in #49,but no-one has bothered to answer.
It should be incumbent on pilots to know the effects of secondary controls...usually Lesson #2 in Basic training..
Likewise with power changes,,and flap selection in this case would have stopped the MCAS.....`Aviate` is the first consideration !!!
It should be incumbent on pilots to know the effects of secondary controls...usually Lesson #2 in Basic training..
Likewise with power changes,,and flap selection in this case would have stopped the MCAS.....`Aviate` is the first consideration !!!
Will Boeing fix the stuck manual trim problem?
Will the FAA de-certify the B737 series aircraft until the stuck manual trim problem is resolved?
Or perhaps, the subject will be quietly buried, to wait for a future opportunity for the problem (inability to manually trim the stabiliser throughout the whole flight envelope) to re-emerge?
Will the FAA de-certify the B737 series aircraft until the stuck manual trim problem is resolved?
Or perhaps, the subject will be quietly buried, to wait for a future opportunity for the problem (inability to manually trim the stabiliser throughout the whole flight envelope) to re-emerge?
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Was trained this in1969 and have trained it ever since. Also seen it trained up to five years ago. Since then? My problem with current training is the loss of the knowledge base developed over many years as new trainers, themselves new train the newer guys and things get forgotten
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Just out of curiosity, looking at the initial report for the last minutes:
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.
How do you recover without unloading (diving) the aircraft?
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.
How do you recover without unloading (diving) the aircraft?
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In my limited understanding of the B-737 MAX MCAS/trim workings, I believe that once the trim Cut Out switches are opened, the only way to trim the stabilizer is via the manual trim wheels. My friends with Boeing experience say that this is a slow and physically taxing operation. To re-trim the horizontal stabilizer quickly would require closing of the trim Cut Out switches, but, of course, that would allow the MCAS to re-initiate the nose down trim action. The pilots would have had a very small window of opportunity (maybe 5 seconds) in which to close the Cut Out Switches, trim ANU, and open the Cut Out switches before MCAS could resume commanding AND.
Just as a matter of interest, I quote from the Boeing 707 Stratoliner Flight Manual, Revision 11-8-60, entitled "Stabilizer Trim Emergency Operation":
"If the stabilizer electric trim becomes inoperative, the manual trim can be used. Due to the flight loads imposed in an out of trim condition, it may be necessary to release the control column to a low force position and retrim while in an "unloaded" condition. If the airplane is much out of trim , this action will have to be repeated until correct trim is obtained."
The manual also stated that the procedure to "Raise Nose" if the stabilizer was jammed nose down was to deactivate the inboard spoilers and raise the outboard spoilers by operating the speed brake lever.
I don't remember where or how I obtained this manual, but I've had it for 30 years or so.
Cheers,
Grog
Just as a matter of interest, I quote from the Boeing 707 Stratoliner Flight Manual, Revision 11-8-60, entitled "Stabilizer Trim Emergency Operation":
"If the stabilizer electric trim becomes inoperative, the manual trim can be used. Due to the flight loads imposed in an out of trim condition, it may be necessary to release the control column to a low force position and retrim while in an "unloaded" condition. If the airplane is much out of trim , this action will have to be repeated until correct trim is obtained."
The manual also stated that the procedure to "Raise Nose" if the stabilizer was jammed nose down was to deactivate the inboard spoilers and raise the outboard spoilers by operating the speed brake lever.
I don't remember where or how I obtained this manual, but I've had it for 30 years or so.
Cheers,
Grog
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Just out of curiosity, looking at the initial report for the last minutes:
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.
How do you recover without unloading (diving) the aircraft?
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.
How do you recover without unloading (diving) the aircraft?
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I did ask the question about airbrakes/speedbrakes in #49,but no-one has bothered to answer.
It should be incumbent on pilots to know the effects of secondary controls...usually Lesson #2 in Basic training..
Likewise with power changes,,and flap selection in this case would have stopped the MCAS.....`Aviate` is the first consideration !!!
It should be incumbent on pilots to know the effects of secondary controls...usually Lesson #2 in Basic training..
Likewise with power changes,,and flap selection in this case would have stopped the MCAS.....`Aviate` is the first consideration !!!
They will kill quite a lot of lift, meaning they will cause the aircraft ROC diminish or even turn the other way all things equal, not what the pilots were looking for.