Re #279 - Optional modification for AoA disagree and EFIS display. ‘…crew has more tools to identify an AOA signal error if one is present and to isolate as to which one seems more reasonable’.
I prefer to consider such displays as adding potential confusion; context is paramount.
‘Reasonability’ implies comparison. With only two inputs there is no direct way to established which AoA is correct (high is in error);
I assume that FCeng et al, are very familiar with these aspects, others less so.
A comparison with stick shake might incorrectly deduce that the high value is correct, or at least it is the immediate risk to flight - stall avoidance.
Similarly, comparison with speed, the mispositioned on-side low-speed awareness (stall) could add to the view that the high AoA is correct.
Subsequent cross check of speed could detect a difference in speed (AoA used for pressure correction), requiring a check of the standby ASI, but short of stalling the aircraft the relationship between an errant AoA input and airspeed cannot be determined. Although it might be concluded that the off-side speed is the better reference, and that with speed increase the stick shake is invalid - false correlation between AoA gauge and stick shake.
This would require a reversal the original mental picture - a demanding task; ‘first learned, best remembered’.
This context represents a piloting viewpoint of additional instrumentation, including mental activity - workload. The view (mental model) provides the reference situation for judging further action.
Many operators demand new, additional displays, yet few are able to argue why these would help avoid situations which they were unable to avoid with existing instruments. Similarly for recovery from upset situations of their own making - excluding system failures.
An engineering / certification argument must never invoke human management of an abnormal situation involving a system failure, which in the first instance was designed to replace human inability to manage the normal situation (boot strapping ?). Also consider the reasonableness of any piloting task.
_
An afterthought, in reversing the above - errant low AoA (high is really correct), then in MCAS terms there is no immediate problem, no stick shake, perhaps a stability weakness - no MCAS when required; other disagree alerts depend on the system logic.
This might imply that to-date, instances of low AoA have not been recorded (or equivalent maintenance flags), or that this type of failure is extremely remote.
Thus why did the AoA fail high - given a choice of direction; vane, wiring, logic ?