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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 5th Apr 2019, 07:23
  #3241 (permalink)  
 
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Turning the wheel was on my type rating course, but featured only one other time in my run of recurrent sims. I would guess that the low houred FO probably had the best recency on a bit of wheel turning.
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Old 5th Apr 2019, 07:24
  #3242 (permalink)  
 
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Originally Posted by Chesty Morgan View Post
I'm sorry but how many hours does one require before one can turn a wheel?
more than 200. There’s a diff between competence and proficiency.

theres a video of a pair of idiots on YouTube who run through a runaway trim procedure. The ‘fo’ cranks the wheel like he’s rolling a drum - meanwhile, the extendable handle sat comfortably in its retracted position.
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Old 5th Apr 2019, 07:33
  #3243 (permalink)  
 
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Originally Posted by Cows getting bigger View Post
Is it not a bit quaint that a 21st century airline manufacturer still believes that a hand-cranked pulley is the best final solution to a complex systems problem?
It is unfortunate, that following the lion-air crash, Boeing and the FAA detailed an AD, that to address a faulty MCAS system, required pilots to disable a perfectly working electric trim system. For a pilot that happened to be appropriately trimmed already, high and not too fast, trimming by the trim wheels is going to be OK. For pilots in more challenging situations, then this was going to be a problem. Both Boeing and the FAA would have been aware of this.

Once the faulty MCAS design had been recognized, it should have been fixed or at the very least, a mechanism introduced and documented, so that a pilot could disable the errant MCAS system without taking out other, important, working systems.
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Old 5th Apr 2019, 07:38
  #3244 (permalink)  
 
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I think there is a reasonable consensus (lest's say 50% chances) that vane shaft broke, keeping AOA vane attached or not, and subsequent alarms and checklists (both useful and useless) threw the crew out of balance. They didn't manage airspeed and lost ability to trim. They reengaged electric trim, was not strong enough either, forgot to CUTOUT, mcas trimmed down, EOF.

I think one of the biggest problems here is the compounding of stupidities. Each stupidity on its own is very much survivable, but all of them is a huge mess.

0. Of course MCAS MUST NOT BE operative with AOA disagree. Minimal software mod.

1. one AOA clearly fails, why not use a switch to transfer everything to the other (manually or automatically). It's a 3 way switch (AOA input L/NORM/R). In the event of stick shaker on, AOA disagree, check if any AOA is stupid (75 is quite stupid), switch to the other side, no more alarms in the cabin, crisis over in 10s tops. minimal wiring loom mod.

Even if you don't do it:

2. We have now perfect data about the influence of AOA over airspeed. 30 knots tops over the full AOA range and airspeed. Probably 15 knots 0 to 15 degrees 0 to 300 knts, probably less than 5 knots in the really tricky areas (slow). Upon AOA disagree, both airspeeds should use a default AOA value (4 deg maybe) instead of throwing UAS. and offer a reading with a possible +-7 knot deviation. But keep autothrottle and autopilot, maybe a caution message (airspeed calculation inacurate, stay 20 knots away from limits). Not a really disturbing unreliable airspeed, just because of a few knots. Minimal software mod.

3. Same with altitude. (altitude calculation inaccurate, stay 1000 feet clear from limits). Minimal software mod.

So that the only remaining alarm would be a stick shaker plus AOA disagree, and you still have autopilots. Much, much easier to handle. But if this is still enough for you to have the aircraft out of trim and miss speed management,

4. If speed goes over 280, message: reduce speed to regain trim ability). Minimal software mod.

My point is: most probably ANY of those mods would have saved the day, and all of them are pretty evident.

To me the problem is simply a huge lack of effort at design level to 1) Imagine 2) prepare for failures.


Chances are that the very same secuence of events, without MCAS final strike, has happened more than once before in other 737 variants (AOA fails, unreliable air data, stick shaker, big confusion, lack of proper aviation and or navigation and possibly all the way to overspeed and uneffective trim). Only without MCAS the aircraft would have been more or less in trim and therefore not nosediving and making the news.

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Old 5th Apr 2019, 07:39
  #3245 (permalink)  
 
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Bjørn Fehrm at Leeham:
Bjorn’s Corner: ET302 crash report, the first analysis

At 7 the aircraft nose is dipping (see Pitch Attitude Disp trace) because PF can no longer hold against the Yoke forces we discussed Wednesday (Ctrl Column Pos L/R). PF decides he needs Electric Trim to stop the aircraft from diving. Cut Off switches are put to Electric Trim active. PF successfully trimmed against the last MCAS attack, he can do it again.

The insufficient trim mystery after re-activation of Electric Trim

After 7 PF commands Electric Trim Nose Up in two short cycles. I asked my selves (as did others) why these short trims? They are fighting to get the nose up to the extent they risk switching in the Electric Trim again. Then why not trim nose up continuously or for at least long cycles once Electric Trim is there? It took me several hours to find an explanation. Here my take:

To understand the blip trims one must have flown fast jets at low altitude. At the speed ET302 is flying, 360kts, it’s hypersensitive to trim. The least trim action and the aircraft reacts violently. Any trimming is in short blips.

As PF holds the nose up with a very high stick force, now for a long time, his sensitivity to release stick with trim is not there (this is what Pilots do when they trim nose up, otherwise the aircraft pitches up fast). He trims therefore in short blips and has difficulty to judge the trim effect he has achieved. His is not flying on feel. He can’t, he is severely out of trim, holding on to the Yoke with a strong pull force.

Anyone who has flown a grossly out of trim aircraft at high speeds knows your feel is compromised. The sensors you have to rely on are your eyes, not your hands.

PF has the horizon glued to read the aircraft. The result is the short nose-up trims we see. The nose goes up and the stick force needed is reduced. His judgment is; this is enough for now. Any MCAS attack I now trim against, then I correct my trim if I need to.

But the aggressive MCAS, trimming with a speed 50% higher than the pilot and for a full nine seconds, kicks in at 8 with a force they didn’t expect. Speed is now at 375kts and MCAS was never designed to trim at these Speed/Altitude combinations. Dynamic pressures, which governs how the aircraft reacts to control surface movements, is now almost double it was when last MCAS trimmed (Dynamic pressure increases with Speed squared).

The Pilots are thrown off their seats, hitting the cockpit roof. Look at the Pitch Attitude Disp trace and the Accel Vert trace. These are on the way to Zero G and we can see how PF loses stick pull in the process (Ctrl Column Pos L). He can barely hold on to the Yoke, let alone pull or trim against.

His reduced pull increases the pitch down further, which increases the speed even more. At 05.45.30 the Pilots have hit the seats again (Accel Vert trace and Ctrl Columns force trace) and can start pulling in a desperate last move. But it’s too late. Despite them creating the largest Control Column movement ever, pitch down attitude is only marginally affected.

We have Control Column displacement this time, JT610 was Force. If the elevator reacts to these displacements, at the Dynamic Pressure we have, we should have seen the diving stop. The lack of reaction to the large Control Column displacement of two Pilots pulling makes me think we now have blowback. This is not a design fault, we are well beyond Vmo. But it explains the rapid dive, unhindered by the Pilots’ actions.

It’s easy to say “Why didn’t they trim then?”. Because they are going down at 20 degrees nose down (which is a lot, a normal landing approach is 3°) and at 400kts. Then you just pull for all you have. And the aircraft is not reacting to the largest Control Column displacement since takeoff. This makes them pull even harder, the aircraft is unresponsive and they are fighting for theirs and all the passenger lives.

A final reflection: Once again we have been given no elevator trace. Why? It’s there, why can’t we see it. It would have given us a better understanding of what’s happening in the last part of the flight.
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Old 5th Apr 2019, 07:42
  #3246 (permalink)  
 
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Reading the report fills me with horror. Two of them, fighting to find the solution, with decreasing success as they are overloaded.

There is too much conflicting information to guarantee that a crew resolves the problem.
  • The aircraft is stalling, yet the pitch/thrust/speed appear correct.
  • As thrust is applied, the stall condition gets "worse", as you have to apply more back pressure to maintain the pitch.
  • The two primary airspeeds are different.
  • The stick shaker is activated, yet the airspeed is high.
  • The airspeed is high, yet the aircraft pitches down as it speeds up, not up.
  • As you speed up, you normally trim down. But it feels like I should trim up.

Stuff that I have never did in the 737 sim:
  1. Found myself with a stab trim that overpowered elevator at max deflection.
  2. The yo-yo or rollercoaster manual trim exercise.

Finally, it needs to be remembered that the deafening stick shaker reduces cognitive ability, and is shaking both control columns, and may therefore be prominent as the "primary" problem.
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Old 5th Apr 2019, 07:53
  #3247 (permalink)  
 
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I've read and imagined the "hipersensitive trim" theory for short blips before the final dive.

I think it is plausible. I think not enough electric trim force is plausible also.

All we need to know the truth is a zoomed in view of the trim units around that time.

I guess it doesn't make any difference, though.
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Old 5th Apr 2019, 07:54
  #3248 (permalink)  
 
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Originally Posted by ecto1 View Post
I think there is a reasonable consensus (lest's say 50% chances) that vane shaft broke, keeping AOA vane attached or not, and subsequent alarms and checklists (both useful and useless) threw the crew out of balance. They didn't manage airspeed and lost ability to trim. They reengaged electric trim, was not strong enough either, forgot to CUTOUT, mcas trimmed down, EOF.

I think one of the biggest problems here is the compounding of stupidities. Each stupidity on its own is very much survivable, but all of them is a huge mess.

0. Of course MCAS MUST NOT BE operative with AOA disagree. Minimal software mod.

1. one AOA clearly fails, why not use a switch to transfer everything to the other (manually or automatically). It's a 3 way switch (AOA input L/NORM/R). In the event of stick shaker on, AOA disagree, check if any AOA is stupid (75 is quite stupid), switch to the other side, no more alarms in the cabin, crisis over in 10s tops. minimal wiring loom mod.

Even if you don't do it:

2. We have now perfect data about the influence of AOA over airspeed. 30 knots tops over the full AOA range and airspeed. Probably 15 knots 0 to 15 degrees 0 to 300 knts, probably less than 5 knots in the really tricky areas (slow). Upon AOA disagree, both airspeeds should use a default AOA value (4 deg maybe) instead of throwing UAS. and offer a reading with a possible +-7 knot deviation. But keep autothrottle and autopilot, maybe a caution message (airspeed calculation inacurate, stay 20 knots away from limits). Not a really disturbing unreliable airspeed, just because of a few knots. Minimal software mod.

3. Same with altitude. (altitude calculation inaccurate, stay 1000 feet clear from limits). Minimal software mod.

So that the only remaining alarm would be a stick shaker plus AOA disagree, and you still have autopilots. Much, much easier to handle. But if this is still enough for you to have the aircraft out of trim and miss speed management,

4. If speed goes over 280, message: reduce speed to regain trim ability). Minimal software mod.

My point is: most probably ANY of those mods would have saved the day, and all of them are pretty evident.

To me the problem is simply a huge lack of effort at design level to 1) Imagine 2) prepare for failures.


Chances are that the very same secuence of events, without MCAS final strike, has happened more than once before in other 737 variants (AOA fails, unreliable air data, stick shaker, big confusion, lack of proper aviation and or navigation and possibly all the way to overspeed and uneffective trim). Only without MCAS the aircraft would have been more or less in trim and therefore not nosediving and making the news.
Fully agreed. There could be much more on the list (e.g. same sound for cabin pressure altitude warning and t/o config, which killed 121 people)
Sensors will continue to break in future. Bits will continue to flip. Wires will continue to fail. Connectors will continue to corrode. People will continue to be humans.
It is the damned duty of every OEM lead design and certification engineer and every FAA, EASA and have you representative to think of possible failure modes and ask for solid and sane design.
It is not the duty to think about saving money by keeping a 40 years old certification in place. Which lets the boss, the boss of the boss and the boss of the boss of the boss smile.
It seems basic airmen and engineering knowledge is lost in the industry and substituted by plain software commodity engineering skills, that are typical for games, desktop software and iOS apps. These do not run airplanes.
Not the only thing that is lost in this world.
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Old 5th Apr 2019, 07:54
  #3249 (permalink)  
 
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What moment does one get from deploying speed brakes ? NU or ND ?

(One of the aircraft I have flown had a partial speed brake deployment with elevator stuck in a ND setting in the C/L....)
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Old 5th Apr 2019, 07:55
  #3250 (permalink)  
 
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Originally Posted by Chesty Morgan View Post
I'm sorry but how many hours does one require before one can turn a wheel?
Chesty, we discussed this earlier, and you said you have flown the 737 with manual trim and it was no problem.
I’ve only tried this a few times, but found the manual trim to be pretty hard. A friend of mine got «Stab out of trim» enroute and diverted because he thought he had a jammed stab. This after he tried manual trim and found it so hard he concluded he had a jammed stab.
It now looks like manual trim is nearly impossible at higher speeds.
It puzzels me a bit that the stab can be trimmed so far it will bring the aircraft out of the pilot’s control. And then you can’t manually bring it back under control because the trim forces are too high.

How Boeing will solve this is beyond me. MCAS is a killer and if they restrict it it will affect the certification. In order to get rid of MCAS they have to redesign the aircraft.
IMHO the MAX will stay on ground for a long time.
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Old 5th Apr 2019, 08:04
  #3251 (permalink)  
 
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Originally Posted by NiclasB View Post
EASA document from Feb 2016 allegedly states that electric trim would not work above 230 knots. That might explain why they re-engaged trim (if the indication that they did re-engage trim is correct)...
Might be a good time to reiterate the relevant part from the document:

"The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides a compensating factor for the inability to use the thumb switches throughout the entire flight envelope. Furthermore, the additional crew procedures and training material will clearly explain to pilots the situations where use of the trim wheel may be needed due to lack of trim authority with the wheel mounted switches."
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Old 5th Apr 2019, 08:10
  #3252 (permalink)  
THUNDERTAILED
 
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Originally Posted by Cows getting bigger View Post
Is it not a bit quaint that a 21st century airline manufacturer still believes that a hand-cranked pulley is the best final solution to a complex systems problem?.
Are the complex systems not the problem? Do you really need an electric trimmer to move a stabilizer in a 15 degree range? Do you really need a electric motor to close your car boot?
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Old 5th Apr 2019, 08:13
  #3253 (permalink)  
 
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Originally Posted by threemiles View Post
Fully agreed. There could be much more on the list (e.g. same sound for cabin pressure altitude warning and t/o config, which killed 121 people)
Sensors will continue to break in future. Bits will continue to flip. Wires will continue to fail. Connectors will continue to corrode. People will continue to be humans.
It is the damned duty of every OEM lead design and certification engineer and every FAA, EASA and have you representative to think of possible failure modes and ask for solid and sane design.
It is not the duty to think about saving money by keeping a 40 years old certification in place. Which lets the boss, the boss of the boss and the boss of the boss of the boss smile.
It seems basic airmen and engineering knowledge is lost in the industry and substituted by plain software commodity engineering skills, that are typical for games, desktop software and iOS apps. These do not run airplanes.
Not the only thing that is lost in this world.
Spot on post. Sums it all up succinctly

Ttfn
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Old 5th Apr 2019, 08:20
  #3254 (permalink)  
 
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I have read all the comments made on this forum concerning the Lion Air, and now the Ethiopian 737 Max crashes. It seems to me that the majority of comments focus on what could, or should, have been done by the crews involved. The Ethiopian pilots especially, whilst doubtless fully knowledgeable of the previous incident, were faced with the extraordinary and bizarre coincidence of a 2nd failure on the Max of the AOA vane, supplying erroneous data to the MCAS. This happened at the worst possible time where they were at their busiest, and with no height or time to play with. Whilst we all now have the benefit of knowledge, hindsight and time to analyse the situation . . . they didn’t. Of course they did their best, attempting to follow the memory items and new procedures as this crisis developed, but who, hand on heart, can lay any blame on them for not getting it exactly right? They may have been an average crew, with maybe less than average experience, but they were a trained and qualified crew and presumably signed off to fly the Max.

Even Boeing chief executive Dennis Muilenburg has publically stated: “As pilots have told us, erroneous activation of the MCAS function can add to what is already a high workload environment”. The Max, and in fact all commercial aircraft, simply have to be designed, built and certified to be within the flying ability of all pilots deemed qualified by their authorities to fly the Max. Two crews have shown sadly that the Max was outside their ability, particularly the 302 crew even with prior knowledge of the potential failure, and the industry therefore has to assume that this is the norm, not the exception.

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Old 5th Apr 2019, 08:23
  #3255 (permalink)  
 
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Originally Posted by ecto1 View Post
...

My point is: most probably ANY of those mods would have saved the day, and all of them are pretty evident.

...
Disagree. May address the issues that caused the latest accident, but contradicts the entire concept of the 737's instrumentation system, and will invalidate the safety calculations on which certification is based, as well as possibly opening the doors to other failure modes.

The 737 instrumentation is a dual-redundant system, comprising two completely separate systems such that in the event of a single failure one completely operational system is still available. With the aid of appropriate disagreement monitors, standby instruments and checklists, pilots are trained to detect and diagnose such failures and take appropriate action.

This system was state-of-the-art at the time the 737 was launched and is still in use in smaller, non-FBW airliners. It is totally adequate for its stated task, that is to provide information to a well-trained human crew. It should never have been allowed to provide inputs to a system that will automatically drive flight control surfaces.
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Old 5th Apr 2019, 08:40
  #3256 (permalink)  
 
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Originally Posted by AfricanSkies View Post
Do you really need an electric trimmer to move a stabilizer in a 15 degree range?
Of course not, you simply turn the manual trim wheel.

About 250 revolutions from full ANU to full AND ...
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Old 5th Apr 2019, 08:56
  #3257 (permalink)  
 
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trim blips

Originally Posted by EDLB View Post
Seems to me that the final hole in the cheese which dictated the outcome of both flights is, that at higher speeds the trim is jammed (in the direction of nose up) if trimmed nose down. On the Ethopian flight a single nose down command by the MCAS system was enough to seal their fate.

I do not believe that in the time where they clung on the column for nose up, that they did not try to use the trim switches to unload the back pressure. Elevator trimming you learn from day one in your SEP trainer.

On the Lion air you can see that the PF did constant fight the MCAS AND trim with nose up. As soon as he transferred command there are only few blips of nose up trim to see on the FDR. Same here on the Ethopian flight.

I can’t believe that you only try with two short blips if the landscape becomes larger fast.
Not a pilot, my field is electronic engineering. The FDR traces on both Lion Air & Ethiopia show short electrical trim ANU blips when longer trim activation would be expected.

I am curious as to where the FDR data for the stabilizer trim is read from - yoke trim switches or the motor drive electronics? Most high power motor drives have feedback that detects if the power demand is exceeded. If this happens, power to the motor is disabled, in order to protect it. Therefore a situation could arise where even though the pilot is activating ANU trim, it results in just a short ANU motor movement, before the motor power limit is exceeded. So if the FDR records from the drive electronics, the trim ANU 'request' by the pilot, will be seen as just a 'blip' although the trim switch is still activated,

This would account for AND trim running the full period as motor power demand is not exceeded (low aerodynamic load), but ANU trim is fighting against high aerodynamic load, which activates the motor protection. Thoughts?
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Old 5th Apr 2019, 09:09
  #3258 (permalink)  
 
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Originally Posted by fizz57 View Post
Disagree. May address the issues that caused the latest accident, but contradicts the entire concept of the 737's instrumentation system, and will invalidate the safety calculations on which certification is based, as well as possibly opening the doors to other failure modes.

.
I read your post and reflected about it. I see your point. We musn't have knee jerk reactions. But open your mind for a second:

Disregarding AOA for speed calculation (for example) will contradict which concept? Which safety calculation will it invalidate? Which other failure mode can you imagine if we do that? (note that the difference is about 5knt at takeoff speed between correct and batshit crazy AOA, so the error between fixed assumed AOA value and real AOA may be as low as 2knts).

Advicing the crew of inability to trim at high speed will harm how? We think it is worthy to throw them an alarm about the AOA heater not heating, and keep the stick shaker all along, but we believe it would be too distracting to remind them that he will loose trim ability due to high speeds?

Those are the official excuses. I don't buy them. It was honestly a very reasonable system when safety was important but not as important as today, data buses did not exist and pilots came from the military.

Not any more.We have better tools now and even if we break concepts and need to recertify things, it is simply too easy today to fool a 737 computer.
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Old 5th Apr 2019, 09:21
  #3259 (permalink)  
 
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https://leehamnews.com/2019/04/05/bj...is/#more-29839

Thinks that the force when electric tirm/ MCAS was switched back on probably bounced the crew out of their seats, causing them to lose/ weaken grip on the controls
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Old 5th Apr 2019, 09:25
  #3260 (permalink)  
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Originally Posted by DaveReidUK View Post
Of course not, you simply turn the manual trim wheel.

About 250 revolutions from full ANU to full AND ...
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
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