Originally Posted by
A37575
Apologies if a similar posting has already been made among the over 4000 posts on the subject. Extract from the Boeing 737-200 Pilot Training Manual February 1982 page 04.80.31. Edited for brevity. Runaway and Manual Stabiliser - Recovery from Severe Out-of-Trim:
. "In an extreme nose-up out-of-trim condition, requiring almost full forward control column, decelerate, extend the flaps and/or reduce thrust to a minimum practical setting consistent with flight conditions until elevator control is established. Do not decrease airspeed below the minimum maneuvering speed for the flap configuration. A bank of 30 degrees or more will relieve some force on the control column
. This, combined with flap extension and reduced speed should permit easier manual trimming.If other methods fail to relieve the elevator load and control column force, use the "roller coaster" technique. If nose-up trim is required, raise the nose well above the horizon with elevator control. Then slowly relax the control column pressure and manually trim nose-up. Allow the nose to drop below the horizon while trimming. Repeat this sequence until the airplane is trim.
If nose-down trim is required, slowing down and extending the flaps will account for a large degree of nose-up pitch. If this does not allow manual trimming then the reverse "roller coaster" can be performed to permit manual trimming."
Boeing "Airliner" magazine published in May 1961 discussed the above subject as it applied to the Boeing 707 by stating: "To trim the stabilizer manually while holding a high stick force on control column. As the airplane changes altitude, crank in the desired trim change. Correct airplane attitude after a few seconds with elevators. Relax stick force again and crank in more trim. Repeat this procedure as necessary until proper 'trim' position of stabilizer is established."
We learned all about these maneuvers in the 1950-60s. Yet, for some inexplicable reason, Boeing manuals have since deleted what was then - and still is - vital handling information for flight crews. Finally, author D.P.Davies comprehensively covers the subject of large trim changes, failure cases and Mach number effect on stabilizers, at pages 38 to 42 in his fine book "Handling the Big Jets," A good case for current airline pilots to buy his book as it is still the best on the market,
IMHO, perhaps if the crews of the ill-fated Boeing 737-800MAX aircraft were familiar with this advice, current as far back as in 1982 and further back still to Boeing 707 types, they could have applied the roller coaster method to gain manual stabiliser control sooner; rather than be caught out by the stabiliser reaching full forward before attempting to trim manually.
Yes it has been discussed here. It was intended to deal with a jet upset at higher level. Davies’ advice likewise.
If you relaxed pull at treetop height you would be in the deck before you could trim.