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Old 16th Jan 2021, 12:55
  #63 (permalink)  
PEI_3721
 
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gums, Detent, et al, caution with specific comparisons.
Following on from zzuf, good refs; - associating the A320 with feel and bob wts could be misleading.

Airbus chose the combination of electrical signalling, digital computation, and side stick as their FBW system. All of these challenged the certification status quo; this required adaptation, interpretation, and new regulations. Airbus designed the future, rewrote the regulations.
Conversely, Boeing, using the improved technologies where possible, chose to follow history. Moving sticks, trim based force-feel, fleet commonality.

The piloting differences matter little (avoiding endless opinionated debate); these aircraft meet the safety requirements, and are flown as any aircraft can be.

Airbus chose a manoeuvre demand algorithm C*, a combination of pitch rate and 'g', with rate dominating low speed, 'g' higher. The trim followup restores a stable condition and minimises drag. (Military systems may favour 'g' more than rate)

Boeing is similar except the trim followup had to maintain the speed-dependent force-feel; this is the basis of the C*U algorithm, where U is the speed aspect.

The 737 Max with MCAS extended previous trimming adjustments (STS), to compensate for aircraft weaknesses; in no way is this FBW (electrical signalling at best). Post modification, MCAS fails safe, no trim demand or incremental runaway (although separately, the stab still could).

Relating this to AF447; the A330 did exactly what the pilot demanded, for the situation, as the crew interpreted it - UAS - pitch/ power. The technical / icing cause had be been identified from previous incidents and modification was in hand. The safety lessons stem from why this one accident differed from several previous incidents with the same trigger - go to previous threads for debate.

In the 737 Max accidents the aircraft did its own thing; crews were in recovery mode without explanation or guidance.

Even after modification, MCAS and the revised checklists could still lead to an AF447 type of incident. The checklist for AoA disagree requires action for unreliable airspeed; this biases the crew's mind to UAS, requiring pitch/power, bypassing wider situational aspects such as cross referring standby instruments which could clarify the situation, not requiring any manoeuvre.
This suggests that Boeing's operational approach to MCAS, alerting and drills, are still out of sync; perhaps not really appreciating if (why) MCAS is required - certification or training.
Old aircraft, even with new mods still require old style situational awareness to help crews understand, without ambiguity, and not presuming any failure, cause, or action. It is difficult to impose new technical philosophies on an old aircraft; similarly for operational aspects.
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