Originally Posted by
BraceBrace
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.
It certainly does seem to be lost in your memory. I've already explained we trained in the rollercoaster manoeuvre in (a Gatwick area) sim in the late '90s. It didn't seem unrealistic at all, far from it. There was no mention of THS being "free floating", this is a technique to recover from a runaway trim that's not been reacted to fast or decisively enough (as, apparently, in both MAX accidents) and enables recovery of ability to re-trim after the force exerted by the control column to maintain level flight has rendered the trim wheel so stiff as to be immovable.
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.