[myth2018]

Boeing has been using only two for quite a time. Having a failed and a working one would simply indicate that something is wrong, but this information is valuable anyway -- it could be used to prevent MCAS from engaging based on wrong data, exactly one of the features the new software update is bringing.

Besides, those AoA sensors are EXTREMELY reliable. So reliable that some have raised the hypothesis that the real problem is not in the sensors themselves, but in some piece of hardware or software between them and the flight computers.

It seems plausible to me since failures in those sensors are too rare in the other planes but, despite that, they allegedly failed in two 737 Max 8s and in a really short timespan.