Originally Posted by
FullWings
...we also don’t know if the MAX or other variants can be manually trimmed at Vmo with the stab a long way out-of-trim forward (the roller coaster doesn’t work at low altitude).
The interim report conducted some tests
1.16.1 SIMULATOR ASSESSMENT OF CONTROL COLUMN AND TRIM WHEEL FORCE (pages 77-80)
copied, paraphrased, my emphasis
3 simulation tests were conducted ... in a CAE manufactured B737 MAX level D full flight simulator
Speed 220 Hands off trim value 6.8
Mis-trim value 2.3, Assessment value
D
Mis-trim value 3.3, Assessment value
C
Mis-trim value 4.3, Assessment value
B
Speed 250 Hands off trim value 6.2
Mis-trim value 1.7
Mis-trim value 2.7
Mis-trim value 3.7 , Assessment value
A
Speed 300 Hands off trim value 5.3
Mis-trim value 0.8
Mis-trim value 1.8
Mis-trim value 2.8, Assessment value
A
A = trim wheel not movable
B = trim wheel barely movable (1 turn not completed)
C = trim wheel moves with great difficulty (2 turns not completed)
D = trim wheel moves with some difficulty (2 turns completed)
It was observed that the greater the mis-trim value, the greater the force required by the pilot
on the control column to fly level flight and consequently the greater the force required turning
the manual trim wheel.
As the trim value from the event flight was around 2.5 units by the time the crew tried to use
the manual trim wheel, even at a speed of 220 kts the difficulty level of turning the manual trim
wheel was level B (barely movable/ 1 turn not completed).
1.16.2 ENGINEERING SIMULATOR AND FLIGHT CONTROL TEST RIG ASSESMENTS (pages 80-82) -
verbatim
(...)
TRIM WHEEL EVALUATION AT THE FLIGHT CONTROLS TEST RIG (FCTR)
Multiple scenarios were executed to run different manual trim Wheel forces for ET-302 flight conditions on ground as well as at different speeds and altitudes using Flight Controls Test Rig (FCTR).
A trim wheel evaluation was performed at the Flight Controls Test Rig (FCTR). Tests were done with aircraft on ground as well as at different speeds and altitudes with different trim settings.
It should be noted that:
- The maximum possible mistrim setting on the FCTR is -1.5 unit.
- 15 wheel rotations are necessary for 1 unit of trim.
- The first test was conducted with aircraft on ground at 0 kt. Expected force on the wheel 10 Lbs.
- It was noted that the wheel was easy to operate, the FCTR matched the physical aircraft very closely and that it was qualitatively close to CAE training simulator forces. The FCTR instrumentation recorded static force of approximately 9.3 pounds.
The second test was conducted with aircraft at 12,000 ft, 250 kts, in trim condition (expected 15 lbs force).
- It was noted that the wheel was a bit more difficult to operate but that it was still doable with one hand. It was qualitatively close to CAE training simulator forces. The FCTR instrumentation recorded static force of approximately 15 pounds.
The third test was performed at 12,000 ft, 340 kts (VMO), in trim condition (expected 21 lbs force.
- It was noted that the trim wheel force become much more difficult to operate than in condition 2. The wheel motion became jerky, straining efforts to turn it. Impact on speech. Qualitatively more difficult than on CAE training simulator. 15 turns would be tiring. Rig instrumentation recorded static force of 21 pounds.
The fourth test was conducted at 15,000 ft and 340kts (VMO), -1.5 units (mist-rim) 14 , expected 35 lbs force.
- It was noted that it was impossible to turn the wheel with one hand confirming the first officer’s statement “it was not working” meaning “hard to move. Some participants expressed surprise at the difficulty. It was possible to turn the wheel with two hands although not convenient at all. The level of force for this condition was found to be between 30 and 40 lbs. It was agreed that difficulty would increase further outside the normal operating envelope (as in the accident case).
The mistrim level on the event flight was 2.5 units at 340 Kts but since the FCTR is limited to 1.5 unit of miss trim, the actual event flight condition could not be tested. Manual trim forces were not attempted in the ECAB as it was not calibrated for the MAX. Manual trim was evaluated in the Flight Controls Test Rig (FCTR).