Originally Posted by
Centaurus
Here is another point of view. There is evidence the aircraft was diving steeply before impact with the water. Regardless what caused the stabilizer to have moved fully forward, there is no doubt the pilots would have been trying to pull out of the dive by pulling hard on the elevator. Extreme air loads caused by high speed would have been working against them. The significant forward position of the stabilizer would be in direct opposition to the elevator position during the attempted recovery; thereby severely limiting the effectiveness of the elevator.
Under the heading Manual Stabilizer Trim, (Boeing 737 FCTM Non Normal Section), the following advice is offered:
"Excessive air loads on the stabilizer may require effort by both pilots to correct mis-trim. In extreme cases it may be necessary to aerodynamically relieve the airloads to allow manual trimming."
To relieve airloads, the crew must momentarily release all backward pressure on the elevator then rapidly wind the stabilizer trim backwards manually or electrically. In turn, this allows more effective elevator control. In other words, a yo-yo manoeuvre. The crew needed to react instantly and correctly to relieve air loads in this manner. Unfortunately, the Lion Air crew did not have the altitude to successfully recover before impact.
I saw this once in a 727 simulator a long time ago. I was FE and the exercise was not runaway trim but somehow the crew got trimmed for fast speed and couldn't get any response with back elevator until they relieved back elevator pressure and then they could trim. My memory is hazy but if you are hand flying and the trim runs for 10 seconds wouldn't sometime in that period the opposite elevator input cause the stab trim brake to engage?