Originally Posted by
DaveReidUK
Bearing in mind that neither of the reports have been published yet, it would be safer to say that on the 737 MAX an AoA indication failure (not necessarily involving a defective vane/transmitter) may (depending on the magnitude and sense of the resulting error) trigger MCAS.
Out of interest, before the grounding were there any recorded instances of a more benign air data failure on a MAX, obviously without producing the JT/ET result ?
My comment is not a full fault-tree analysis, and there are several sub-cases of AOA failure on the MAX. In particular nose down or 'small' disagree value would not trigger MCAS. Since AOA disagree was not enabled on many aircraft (as per software fault), those rare cases were unlikely to be recorded in detail.
Edit: As to why the known AOA failures only occurred on the captain's side of the aircraft, that may be a combination of bad luck, and the use of air-stairs on that side. There are no known cases where the AOA failed on the side that was not being used by MCAS.
Despite repeated requests, nobody on this forum has produced hard evidence, so we must assume that such data does not exist (partly for the reasons I mention above). Perhaps some events were noted anecdotally, but a full FDR download was not warranted, and the data was overwritten.
Edit: In theory there could have been a safety case for monitoring AOA data more closely, but given the other failures and delays in grounding the MAX, this is 20/20 hindsight.