737 Stuck Manual Trim Technique
Join Date: Jan 2008
Location: Netherlands
Age: 58
Posts: 36
Likes: 0
Received 0 Likes
on
0 Posts
Join Date: Apr 2018
Location: KDCA
Posts: 26
Likes: 0
Received 0 Likes
on
0 Posts
Ostrower has a copy of the 1982 FCTM with a description of "roller coaster" technique:
https://theaircurrent.com/wp-content...-1240x1903.jpg
(main article)
https://theaircurrent.com/wp-content...-1240x1903.jpg
(main article)
Join Date: Dec 2015
Location: Cape Town, ZA
Age: 62
Posts: 424
Likes: 0
Received 0 Likes
on
0 Posts
Ostrower has a copy of the 1982 FCTM with a description of "roller coaster" technique:
https://theaircurrent.com/wp-content...-1240x1903.jpg
(main article)
https://theaircurrent.com/wp-content...-1240x1903.jpg
(main article)
Join Date: Apr 2015
Location: Under the radar, over the rainbow
Posts: 790
Likes: 0
Received 0 Likes
on
0 Posts
Join Date: Mar 2019
Location: Zurich
Posts: 1
Likes: 0
Received 0 Likes
on
0 Posts
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.
Join Date: Aug 2008
Location: Airborne
Age: 63
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
Flaps extended . . . . . . . . . . 10° and 80% N1
Flaps up . . . . . . . . . . . . . . . . 4° and 75% N1
Join Date: Jul 2002
Location: Netherlands
Age: 71
Posts: 165
Likes: 0
Received 0 Likes
on
0 Posts
Not active any more but I never forgot the Convair accident due to a reversed trim:
https://www.flightglobal.com/news/ar...cables-326251/
The last weeks It crossed my mind I might have tried to trim even more nose down, in a desperate last attempt to see if the nose would come up...Which in this case would only have sped up the outcome of course...
Remember, those guys were loosing it big time, they were desperate...
Many accidents I have played back in my mind ( a kind of survival procedure for me to deal with terrible accidents), with me making the right decisions and saving the day.
But there are a few cases where I cannot find a realistic better outcome. Like JAL123. I think this MCAS affair is close to that, although technically it was survivable. But You would have to get immediately into the right direction of thinking.
How many times in YOUR career the SIM had to be stopped because Your crew was going down the drain, following a completely wrong lead? I was stopped at least once if I remember correctly....
https://www.flightglobal.com/news/ar...cables-326251/
The last weeks It crossed my mind I might have tried to trim even more nose down, in a desperate last attempt to see if the nose would come up...Which in this case would only have sped up the outcome of course...
Remember, those guys were loosing it big time, they were desperate...
Many accidents I have played back in my mind ( a kind of survival procedure for me to deal with terrible accidents), with me making the right decisions and saving the day.
But there are a few cases where I cannot find a realistic better outcome. Like JAL123. I think this MCAS affair is close to that, although technically it was survivable. But You would have to get immediately into the right direction of thinking.
How many times in YOUR career the SIM had to be stopped because Your crew was going down the drain, following a completely wrong lead? I was stopped at least once if I remember correctly....
fdr said
The design defect of immovable manual trim wheel in the pitch control system under some conditions was obviously acceptable to the FAA 50 years ago to allow certification of the B737 aircraft type.
Grandfather rights on existing certification of the B737 aircraft type has somehow allowed this defect in the flight control system to continue to exist in the modern era.
The high authority automatic MCAS system combined with the low authority manual electric trim system for the pilot to counteract the MCAS, has now shown up this "hidden" design defect in a most dreadful way.
The design defect of the immovable trim at high aerodynamic loads has been festering for 50 years awaiting a system that would reveal it to be a fatal design flaw.
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.
Forget about MCAS, how on earth is the procedure in the FCTM reasonable or acceptable.
Grandfather rights on existing certification of the B737 aircraft type has somehow allowed this defect in the flight control system to continue to exist in the modern era.
The high authority automatic MCAS system combined with the low authority manual electric trim system for the pilot to counteract the MCAS, has now shown up this "hidden" design defect in a most dreadful way.
The design defect of the immovable trim at high aerodynamic loads has been festering for 50 years awaiting a system that would reveal it to be a fatal design flaw.
Thread Starter
It certainly was neither violent nor extreme manoeuvering, you're only pulling to as much of a normal climb attitude as you can reasonably acheive and then relaxing back to level flight. Pax would find it a bit of an undulationperhaps like flying through wave but to call it "yo-yo' is a big exaggeration. Even roller-coaster greatly overstates it although it illustrates the shape of the thing, if you like.
Next time you're in the sim ask to try it. It's quite a gentle flightpath as you're pulling big forces on the yoke at first.
I'm surprised it disappered from the FCOM though. Mr Boing's gonna regret that decision...
Min height to do this at? 500 feet if you had to - not that you'd choose to do of course. There should be no diving or descent involved, just undulations up from and back to whatever altitude you started from. If you had height to spare ypu might use a bit of descent but it wouldn't be to my taste, I'd not want the nose below the horizon with extreme down-trim simply because of the recovery, and also to avoid airspeed buildup which would surely be obvious to most.
Join Date: Dec 2005
Location: Frisco, Texas USA
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
Has anyone read the preliminary report here? They used the electric trim 30 seconds before the crash. MCAS responded again. Airspeed was about 350 KIAS.
So, it would seem to me that if the electric trim could move the wheel, and that it can be stopped and overridden by hand power, that manual trim should have worked. 350KIAS should NOT be too fast for manual trim. Since they followed and summarily rejected the QRH and improvised, then who is at fault, or at least share fault? 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. I'll give the Lion Air guys a bit of a pass, but not much. They have a horrible reputation in the training department.
But what do I know. Six airlines in four countries on the B737 and I teach on it. Read the reports. Read them with a skeptical eye. They are surprisingly incomplete.
So, it would seem to me that if the electric trim could move the wheel, and that it can be stopped and overridden by hand power, that manual trim should have worked. 350KIAS should NOT be too fast for manual trim. Since they followed and summarily rejected the QRH and improvised, then who is at fault, or at least share fault? 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. I'll give the Lion Air guys a bit of a pass, but not much. They have a horrible reputation in the training department.
But what do I know. Six airlines in four countries on the B737 and I teach on it. Read the reports. Read them with a skeptical eye. They are surprisingly incomplete.
Originally Posted by HalinTexas
Since they followed and summarily rejected the QRH and improvised, then who is at fault, or at least share fault?
Then there were momentary electric trim inputs; I think they realised that they didn't have enough pitch control and decided to try the electric trim again. What would you have done? Just sat there with the switches off because that was the end of the QRH drill and slowly speared in?
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.
Join Date: Dec 2005
Location: Frisco, Texas USA
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
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.
Originally Posted by HalinTexas
Anyone that hand flies the airplane much knows that you have to trim the hell out of Boeings
Crews with little general aviation experience just aren't getting enough practice to survive these types of events, and it's not their fault.
Join Date: Jul 2006
Location: Sand Pitt
Posts: 121
Likes: 0
Received 0 Likes
on
0 Posts
Join Date: Apr 2009
Location: Hotel Gypsy
Posts: 2,821
Likes: 0
Received 0 Likes
on
0 Posts
Since they followed and summarily rejected the QRH and improvised, then who is at fault, or at least share fault? 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.
1. Aerodynamic development that led to poor static stability at high AOAs.
2. Inadequately deigned software add-on (MCAS) to
3. Single point of failure (AOA gauge) in safety critical flight control system.
4. Inadequate training and documentation.
5. Poor Boeing assessment of systematic failures that led to Lion Air crash - initial AD.
6. Failure by Lion Air #1 to articulate and capture problem after first, non-fatal event.
7. Regulatory oversight, lack of?
8. Two slightly dull/average/unlucky crews faced with multiple inputs.
I'll wager that the crew 'percentage' will not be the biggest number.
Join Date: Dec 2015
Location: Cape Town, ZA
Age: 62
Posts: 424
Likes: 0
Received 0 Likes
on
0 Posts
Time to repost this (or similar) article link every time someone also asks about:
- how do manual trim wheels, cables and the jackscrew work
- why the horizontal stabiliser is loaded via opposing elevator aerodynamic forces
- alternative techniques for unloading the HS jackscrew (roller coaster)
- why didn't the pilots do X or Y?
- can the plane fly inverted?
- why was this certified?
See: https://theaircurrent.com/aviation-s...nvestigations/
Edit: +1 for Cows getting bigger
- how do manual trim wheels, cables and the jackscrew work
- why the horizontal stabiliser is loaded via opposing elevator aerodynamic forces
- alternative techniques for unloading the HS jackscrew (roller coaster)
- why didn't the pilots do X or Y?
- can the plane fly inverted?
- why was this certified?
See: https://theaircurrent.com/aviation-s...nvestigations/
Edit: +1 for Cows getting bigger