Originally Posted by
EDLB
+1
The 737 safety philosophy means that it turns into a conventional stick and rudder aircraft once you turn the AP off. And that with redundant left and right seat set of controls. The PF assumes in AP off mode that he has full authority on the flight controls and surfaces. There are automatic flap retract in over speed left but that does not reduce his controll over the aircraft.
If you brake that philosophy by introducing “features” overriding PF control inputs they need to be full FBW worth with all fail safe features needed for a FBW control.
With the two accidents it came out, that the manual trim wheel can not be actuated manually in a high elevator deflection and high speed situation.
Your first point is the heart of the matter. When faced with any aircraft control problem, the pilot needs to be able to quickly revert the aircraft to a configuration in which he knows what he is dealing with. In the old style mechanically controlled planes such as the 737, this was easily achieved with the autopilot disconnect button. Further, old guys like myself, grew up with these systems. I started flying transport category aircraft when an autopilot was simply a wing leveler and pitch or altitude hold. Manual flight was routine for climbs and descents. My generation needed to be encouraged to embrace auto flight as it matured. We were spring loaded to dump it and manually fly if we got behind. As the years moved on we started to have new/younger pilots whose only experience was systems, auto flight and flight management computers that could handle all phases of flight except initial takeoff. We were encouraged to use these systems fully to reduce workload and to increase our ability to maintain a lookout for traffic, terrain, volcanic cloud, cb, whatever. This advancement was wonderful but it also came with a problem. Over time, hand flying skill and instrument scan was degraded, especially in those who did not have a lot of experience hand flying in vertigo and anxiety inducing circumstances. This resulted in a disability where autoflight could, depending on the individual, become a crutch rather than a tool. The pilot with this disability needed, in any crisis, to first get auto flight operating. This is not a big problem in most circumstances but is a very big problem when the issue is basic aircraft control.
To your second point. I do not know if this is a fact and it seems like it should have been a certification issue if it is. I would not accept any simulator demonstration but would expect that it has been demonstrated in the actual aircraft that the manual, hand crank, stab trim is operable throughout the envelope of the aircraft, speed up to Vmo, altitude, thrust setting, g loading, Cg. If this was not done, it is a problem. If there is a speed limit to manual stab operation, the pilots should be told, even it is just a note that it was not demonstrated to work in excess of Vmo , or whatever speed it was tested to.