The Roller Coaster technique in Boeing 737's
Joined: Nov 1999
Posts: 647
Likes: 19
From: East side of OZ
I remember when I flew B707s way back when that if the stab ran away that full up elevator control was equivalent to four units of stab trim so if you didn’t catch the runaway before that then you were left with little or no pitch control and the only option was the roller coaster procedure that we practiced in the sim.
Cheers,
BH.
Cheers,
BH.
Joined: Feb 2003
Posts: 543
Likes: 338
From: Blue sky
The rollercoaster technique wouldn't be needed. As far as I can tell, the only scenario in which the rollercoaster technique could've become necessary would be a trim brake failure. In that scenario, the motor wouldn't be operating but the stabilizer would move freely and would react to aerodynamic loads. The only way to regain control would be to grab the trim wheel(s), bring it to a stop, and then hold onto it for the remainder of the flight (or at least be ready to grab it again if needed). This is the reason for the final step on the Runaway Stabilizer checklist (Trim Wheel...Grab and hold).
If the THS is "free-floating" in the wind, you can "control" the trim through the elevator, but the weird thing is that the actions are completely opposite to the "normal". If I recall correctly, if the trimwheel is continuously trimming nose down, you have to push the elevator full down and it will stop the runaway. You don't use the elevator to "control the nose movement", but you use the elevator to "control the THS movement". And in that case, the elevator actions are completely opposite to the rollercoaster. You create a force that moves the THS in the direction you want it to move and you don't even need to touch the trimwheel to retrim. It will rotate by itself, you just have to know how to steer the elevator. If others have more information, feel free, as this is really long lost in my memory... I'm not aware of any sim that is capable of simulating this recovery procedure.
In the end, all these procedures are nice to know if you know what you are doing, but can lead to gigantic disasters if you don't really know what you are doing. Just stop the runaway in time and continue with what you have as you should have plenty of controllability. You shouldn't be doing testpilot recovery procedures.
Last edited by BraceBrace; 23rd May 2026 at 09:26.
Joined: Mar 2018
Posts: 2,265
Likes: 1,167
From: Central UK
Which brings on another topic of another recovery procedure that is completely forgotten and where things might get really confusing if you start with these recovery procedures.
If the THS is "free-floating" in the wind, you can "control" the trim through the elevator, but the weird thing is that the actions are completely opposite to the "normal". If I recall correctly, if the trimwheel is continuously trimming nose down, you have to push the elevator full down and it will stop the runaway. You don't use the elevator to "control the nose movement", but you use the elevator to "control the THS movement". And in that case, the elevator actions are completely opposite to the rollercoaster. You create a force that moves the THS in the direction you want it to move and you don't even need to touch the trimwheel to retrim. It will rotate by itself, you just have to know how to steer the elevator. If others have more information, feel free, as this is really long lost in my memory... I'm not aware of any sim that is capable of simulating this recovery procedure.
In the end, all these procedures are nice to know if you know what you are doing, but can lead to gigantic disasters if you don't really know what you are doing. Just stop the runaway in time and continue with what you have as you should have plenty of controllability. You shouldn't be doing testpilot recovery procedures.
If the THS is "free-floating" in the wind, you can "control" the trim through the elevator, but the weird thing is that the actions are completely opposite to the "normal". If I recall correctly, if the trimwheel is continuously trimming nose down, you have to push the elevator full down and it will stop the runaway. You don't use the elevator to "control the nose movement", but you use the elevator to "control the THS movement". And in that case, the elevator actions are completely opposite to the rollercoaster. You create a force that moves the THS in the direction you want it to move and you don't even need to touch the trimwheel to retrim. It will rotate by itself, you just have to know how to steer the elevator. If others have more information, feel free, as this is really long lost in my memory... I'm not aware of any sim that is capable of simulating this recovery procedure.
In the end, all these procedures are nice to know if you know what you are doing, but can lead to gigantic disasters if you don't really know what you are doing. Just stop the runaway in time and continue with what you have as you should have plenty of controllability. You shouldn't be doing testpilot recovery procedures.
My immesiate reactions on learning details the MAX accidents were 1) why the digamma didn't they react to what was obviously a runaway trim by operating the cutout switches and 2) if control was hard to maintain by control column alone whey didn't they roller-coaster - not realising that this (far fron "test pilot" manoeuvre) had been removed from the book and maybe they didn't know it. I was astounded to learn thst it was no longer included - along with a whole bunch of other potentially useful but rather esoteric stuff like variations on battery starts and in-flight FMC resets that we had in our FCTM and did in the typre conversion course, admittedly with a very old-school instructor who thought this stuff important.
Joined: Dec 2002
Posts: 2,776
Likes: 353
From: UK
Boeing shackled to the past - man or machine
RCTechnique - an old, ancient view of safety certification which claimed a piloting contribution in meeting requirements.
Long past its best-before-date, but with Boeing's policy of Grandfather Rights in the 737, and their design philosophy it was been retained.
Hindsight reminds us that human involvement cannot be quantified or prejudged.
Pre 1980s
https://www.dropbox.com/scl/fi/7wivz...=z97cebal&dl=0
"Boeing shackled to the past - man or machine."
Others consider the future - man and machine, together.
But who will embrace the next change; not a step jump, but a slow evolution so as not to disturb the current levels of safety.
Long past its best-before-date, but with Boeing's policy of Grandfather Rights in the 737, and their design philosophy it was been retained.
Hindsight reminds us that human involvement cannot be quantified or prejudged.
Pre 1980s
https://www.dropbox.com/scl/fi/7wivz...=z97cebal&dl=0
"Boeing shackled to the past - man or machine."
Others consider the future - man and machine, together.
But who will embrace the next change; not a step jump, but a slow evolution so as not to disturb the current levels of safety.
Joined: Feb 2003
Posts: 543
Likes: 338
From: Blue sky
Thanks, yes. If it's a "trim system failure", the yoke cut-out switches stop the runaway. If the brakes on the jackscrew fail, the yoke cut-out doesn't work and you need to grab the trimwheel and stop it immediately. In the first case, if manual trim is required but unable, the rollercoaster is an option. However, doing a rollercoaster with a free floating THS seems complicated to do from a CRM perspective. The easier solution shown to me was to "use the elevator to control the THS" to get in trim which requires opposite elevator movement to the rollercoaster.
