Originally Posted by
ATC Watcher
There are lots of Rumors going round in Africa ( the mother of rumors ..) about the Capt having done all the works as trained, incl STAB TRIM cut out and all, but could not overcome the final dive manually .
I do not believe in rumors, especially not in Africa, but a question for those here with experience on the 737.
Is there a speed above which the air pressure on the control surface of the horizontal stab would start to prevent a standard human to activate normally the manual trim wheel ? and btw is this force accurately duplicated in a sim as speed builds up ?
I have flown some ( old) GA aircraft where above a certain speed the cables would just spin around the pulley not moving the stab ( e.g the Super Cub in a steep dive, where lever will turns with difficulty , but does not move the Stabilizer , and before you ask, this happens well below VNe )
I do not believe this would be possible in a modern airliner, but ask the question just in case. .
The thread:
Boeing advice on "aerodynamically relieving airloads" using manual stabilizer trim covers more-or-less the same thing I think. It's not that the cables spin without moving the stab (as with your Super Cub), it's that you won't be able to move them until aero loads are reduced.
I don't think it's clear (even having read that thread) whether or not it can still happen on newer 737s, but it may not have mattered for the ET crew. If your rumour is true it wouldn't be a great surprise, they were low (AGL) and fast, time to correct any mis-trim would be small. They had the unenviable choice between fighting the machine with the pickle switches (machine will win eventually, it's faster, it doesn't get tired, or distracted etc.) or hitting the cutouts and winding the handle, which is slow. The ground is rising...