Originally Posted by
jugofpropwash
The underlying issue here seems to me that regardless of whether the MCAS is a good system, it's not going to cause a problem unless there's a sensor failure. If this crash turns out to have the same cause as the first, then that means two bad sensors, on virtually new aircraft belonging to two different airlines. Wouldn't this be an abnormally high failure rate on a critical part?
One thing that was I wondering after the Lionair accident, was what are failure rates of the AoA vanes in general. Are they more or less reliable than the pitot-static systems they complement? This is fairly critical when a single vane in the MAX can provide the input to move the stab in MCAS.
My understanding is on the NG, a single vane failure indicating high alpha will generate indications only, i.e a stick shaker on one side and a probable IAS disagree due to an AoA input to IAS calculation. This is somewhat confusing with no AoA disagree annunciation (it certainly seemed to confuse Lionair maintenance who paid attention to to the working pitot-static system and not the failed AoA vane prior to the accident flight.
For any 737 pilots present, would an erroneous stick shaker activation due to faulty AoA data be something not incredible within a career?