Originally Posted by
Derfred
There has been very little discussion here on the subject of false stick shaker on rotation.
Lion Air had it on two flights. That we know.
Whilst we don’t yet know anything about Ethiopian, the initial flight profile looks to me like a pilot reaction to a false stick shaker - very slow/erratic climb and rapidly increasing airspeed. Assuming they took off with flaps extended, MCAS would not have contributed to the early part of this profile. The rapidly increasing airspeed may have led them to pull flaps up during the confusion, which may have then led to an MCAS activation.
Identifying false stick shaker on rotation has not formed part of any simulator training I have experienced.
I think that is an excellent description of the sequence of events, and the interaction between the computer and the crew in both events.
AFAIK most checklists are not aimed at instantaneous diagnosis of the underlying fault, but rather a patchwork of responses to different flight control situations.
IMO false stick shaker activation (in isolation) is a hazardous condition, because of the additional stress imposed on the crew during a high workload situation. The fact that it cannot be turned off, means it is an ongoing source of distraction, which then becomes a factor for subsequent events.
I would speculate that false MCAS activation on its own (in the absence of any distractions) could have been a more survivable situation, because the crew could focus all their attention on that one single failure. The reality may be that they were already in a 'tunnel vision' hazard evaluation mode, and the MCAS activation was too insidious to be immediately recognised. The 3rd pilot in the earlier Lion Air flight was able to be more objective, outside this process.
I cannot think of any other scenario where false stick shaker activation would present an immediate hazard, which might be why it has not been a training issue. The situation with AF447 was the opposite kind of fault, where the aural stall warning (not stick shaker) was valid but only intermittently active (due to software inhibition), which led to additional confusion.
Edit: My post was drafted before the WSJ article was posted.