Wheelsright, #5014
Re Old MCAS. We cannot assume that crews knew of MCAS interaction with trim, (Boeing did not publish details).
With some knowledge (ET), the procedure called for use of trim and / or deduction of trim malfunction. See discussions on time assumed to recognise malfunction - MCAS active/quiescent cycle would take at least 13 sec of dedicated observation, thus probably much longer; then follow the trim runaway drill.
(5 sec could have been the value used in certification for trim runaway - but MCAS is not continuous)
An AoA alert only adds to the general confusion of several alerts consequential to AoA malfunction.
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Re ground inhibit of AoA. As reported the logic appears reasonable. AoA vane requires airflow thus is inaccurate until xxx kts, but it is required soon after rotate for the critical stick-shake function.
Disagree provides no benefit in this, but even with contrary arguments, inhibition of superfluous alerts below 400 ft is reasonable.
I suspect that the AoA mess originates from dominant customers request for AoA display (gauge), similar to 757 option. Their reasoning driven by cost to meet the then emergent upset recovery training - we have AoA display thus less / no additional training. Boeing said yes, but possibly added the disagree alert to overcome the ‘misleading’ information certification aspect with AoA malfunction - gauges show different values but not which is incorrect.
The better engineering solution is to remove the display - AoA Disagree not required, MCAS inhibited, … no additional training, install new alert that MCAS is inoperative.