kalvado wrote:Boof02671 wrote:Show us the incidents.
Here you go:
Though this incident, and it is almost certain to be one incident reported by both crew members, was almost assuredly not an MCAS incident. The reason why is it stopped when the autopilot was disconnected. The concern of the pilots, in light of the lack of MCAS information in the FCOM was that there might be other corner cases they didn't know about. This would be a completely reasonable concern. There are not cases in the ASRS data to last week that included uncommanded stabiliser trim down in non-autopilot operation. There are, however, other cases of 737NGs having uncommanded descents and trim down in autopilot operation. Now ASRS only covers US carriers, but it is very well used, so there is a high likelihood that and US MCAS failure would have been reported.
As for a tendency to pitch up at high-thrust, low-speed, high AOA. This exists already in the 737NG, and other a/c with wing mounted engines. At least one Boeing FCTM for the 737NG has this in it
To recover from a stall, angle of attack must be reduced below the stalling angle. Nose down pitch control must be applied and maintained until the wings are unstalled. Application of forward control column (as much as full forward may be required) and the use of some nose-down stabilizer trim should provide sufficient elevator control to produce a nose-down pitch rate. It may be difficult to know how much stabilizer trim to use, and care must be taken to avoid using too much trim. Pilots should not fly the airplane using stabilizer trim, and should stop trimming nose down when they feel the g force on the airplane lessen or the required elevator force lessen.
Under certain conditions, on airplanes with underwing-mounted engines, it may be necessary to reduce thrust in order to prevent the angle of attack from continuing to increase. Once the wing is unstalled, upset recovery actions may be taken and thrust reapplied as needed.
The MAX will be different to the NG, but it will still have manny of the same characteristics, so it is fairly easy to see the logic that Boeing had when looking at what to/not to change in the manuals. They already had info about thrust and stall plus telling pilots that you do have to trim to get out in some cases. It is also quite easy to see how this is flawed logic. Especially since the NG wording would be somewhat confusing on the Runaway Stab correction:
Hold the control column firmly to maintain the desired pitch attitude. If uncommanded trim motion continues, the stabilizer trim commands are interrupted when the control column is displaced in the opposite direction.
Manual Stabilizer Trim
If manual stabilizer trim is necessary, ensure both stabilizer trim cutout switches are in CUTOUT prior to extending the manual trim wheel handles.
Excessive airloads on the stabilizer may require effort by both pilots to correct the mis-trim. In extreme cases it may be necessary to aerodynamically relieve the airloads to allow manual trimming. Accelerate or decelerate towards the in-trim speed while attempting to trim manually.
Would pilots that have tried the first automatically think to do the second when the first was insufficient?
Also, the manual has information on Elevator Blowback, as mentioned in Leehman, though it is buried in the Stall recovery bit:
Nose Low, Wings Level
In a situation where the airplane pitch attitude is unintentionally more than 10 degrees nose low and going lower, the airspeed is increasing rapidly. A pilot would likely reduce thrust and extend the speedbrakes. Thrust reduction causes an additional nose-down pitching moment. Speedbrake extension causes a nose-up pitching moment, an increase in drag, and a decrease in lift for the same angle of attack. At airspeeds well above VMO/MMO, the ability to command a nose-up pitch rate with elevator may be reduced because of the extreme aerodynamic loads on the elevator.