Originally Posted by
MechEngr
We have two crashes because the AoA system lied. I don't need to fly a plane to know that.
It should have told the truth and signaled the equivalent of "The data is wrong" instead of reporting an erroneous 70 degree nose up AoA (ET302).
In both crashes the stall warning system, based on the AoA lie, caused aural and stick shaker warnings and disabled the autopilot, confusing the pilots about the status of the planes, which were not near stalling. The pilot's ability to detect MCAS actuation was adversely affected by the false warnings. Had that status been available to the MCAS systems engineers they are very likely to have added that state as a consideration in inhibiting the operation of the stabilizer trim motor, but they apparently believed AoA was reliable. It was an error to believe that, but the AoA subsystem developers would be the ones most familiar with the reliability of the AoA system.
So why didn't the aural stall warning group, the stick shaker group, or the autopilot group ever notice that the AoA could be unreliable and force the development of a clear indicator to the pilots about the reason for all three of them dumping on the pilots at the same time?
As you don't fly the type I will try to keep this comment on a level playing field.
Sensors installed on most modern transport aircraft "don't lie". That's why I asked the question regarding your comment. Systems that are not in agreement in data feeds generally provide pilot (s) "feedback" either through EICAS or by alerting the pilots through respective PFD's (or ND's) such as a horizontal amber line drawn through the respective failed modes on the PFD for LOC/VNAV/LNAV or VTK (inop FMC) on respective pilots ND.
When you consider the vast amount of users reading these posts, it is very easy to draw conclusions from posts, such as yours, that systems "lie", which may not be correct, so I wanted to clarify your post.