CONSO - I appreciate your summary list and agree with much of what you have presented. Below I have added my thoughts and a few points of clarification using italic text. The non-italic text below are the summary statements provided by CONSO.
1) AOA mismatch notice/display an optional item- no doubt at a ridiculous cost- so pilots had no notice of that discrepancy
- Agreed - neither did the engineers.
2) AOA single input with no matching- voting allowed to directly affect/move a critical flight control item ( stabilizer )
- Yes. Analysis determined that one increment of MCAS stabilizer motion by itself did not pose a safety issue. No second increment without pilot trim input. Design approach assumed pilot trim input would return airplane to trim prior to any subsequent MCAS activation.
3) Pilots of 737 prior to Max ‘knew” that push pull of control column in opposition to autopilot would disengage autopilot and allow manual- direct control until autopilot manually reset/engaged
- Push / pull on column does disengage autopilot (if engaged) and at all times provides direct control of elevator. Same for all 737 models.
- Autopilot box, however, continues to provide automatic stabilizer control even when autopilot function is disengaged:
- STS on earlier 737 models
- STS and MCAS on 737 Max
4) description of runaway stabilizer infers continuous movement despite column disconnect or no trim switch.- thus a positive action tripping circuit breaker is needed to stop
- Agreed from wording I have seen here in PPRUNE.
5) But MCAS- HAL on 737 MAX ignores both column and trim switch use- and moves stabilizer and then STOPS briefly- ALL dependent on ONE AOA value- with NO notice, NO display, and NO warning
- 737 Max does not ignore column or pilot trim switch. Column is sole control driver for elevator. Pilot trim has priority over automatic control of stabilizer. One difference is that pull column disables automatic airplane nose down STS command while pull column does not disable airplane nose down MCAS command.
- All 737 stabilizer motion involves turning of cockpit stabilizer trim wheels (one at each pilot's inboard knee) with ten revolutions of approximately 8" diameter, one inch wide wheels per degree of stabilizer motion. Wheel turn produces considerable noise as well (ranted not as significant when stick shaker is going.)
6) Neither instruction manual or training mentions the absolute authority of MCAS- HAL- so pilots believing and trained that pull or push on control column, and/or disconnecting Autopilot gives them ABSOLUTE manual control at ALL times and that trim switch still works( briefly)
- I cannot comment on instruction manual or training.
- No argument with this comment other than to restate that pilot stabilizer trim input via wheel mounted thumb switch always stops and overrides automatic stabilizer control whether coming from STS or MCAS functions.
7) Pilots are now faced with a WTF conundrum. They are going too fast to lower flaps which stops MCAS-HAL and at a low altitude per training - “runaway” stabilizer seems to stop for a while- and autopilot is off so ????
- Agreed. Design assumed that pilots would recognize improper stabilizer motion taking them repeatedly away from trim when flying relatively steady condition and take the action of cutting out stabilizer motors. I cannot speak to the associated manual nor training.
8) Meanwhile stick shaker rattles, trim wheel starts and stops and ????
- Agreed - quite the compound mess. Don't forget that they are also seeing air data miscompares (speed and altitude) and havd associated warning lights to potentially take their attention away from improper automatic stabilizer motion.
And only a few minutes to solve . . . " I'm sorry dave . . "
- Must continue to fly the airplane vertical/pitch axis with column and use control wheel mounted stabilizer trim switches to offload column forces while sorting out the situation. HAL never said "I'm sorry Dave", but HAL did continue to give errant nose down stabilizer increments that seem to have eventually overwhelmed Dave.
Let me add that with this and all of my entries on this topic I am not trying to place blame for this tragic accident on any one party. I am merely trying to shed some light on how the system involved functions so that all can better understand what this crew faced.
May all of those 189 souls rest in peace and everyone they left behind find the support and comfort that they need to face life after this horrific loss.
Respectfully submitted - FCEng84