PPRuNe Forums - View Single Post - Boeing 737 Max Recertification Testing - Finally.
Old 5th Aug 2020, 12:33
  #201 (permalink)  
safetypee
 
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derjodel, # 196

The weakness of your point is the assumption that the nacelles change AoA; they do not. The change is in the relationship between stick force and speed (AoA) - the longitudinal stability.

At constant speed, AoA is increased by moving the stick and pitching the aircraft. Thus with the first high AoA 'event' - trim down, the stick force will increase, providing a force-feel feedback to the pilot. This change encourages the pilot to move the stick forward to reduce stick force and thus reduce AoA ( normal flying technique for speed / AoA change ).
There is a risk that the pilot will accept or even increase stick force - manoeuvring the aircraft to a higher AoA, this is like any other aircraft. MCAS was intended to achieve a similar stick force-to-speed (AoA) relationship the NG; i.e. the Max will feel the same as the NG and still meet the certification requirements even with the larger engines.

The MAX can be stalled, as the NG. One MCAS input might be judged as sufficient to cue pilot awareness of a deceleration / manoeuvre, but never intended to prevent a stall.
The aircraft stall characteristics would be the same with / without MCAS, although without MCAS the potentially lower stick force during recovery could encourage re stalling.

Big Pistons,

The FCCs will now be cross monitored to limit trim failures within a range where manual control is acceptable (13.3).
Non FCC related failures, e.g. stab trim runaway, are not protected - as in the NG, but wiring changes in the MAX reduce the likelihood of failure, the corrective action for which still relies on timely pilot intervention (13.6).
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