[js2]

> The classic approach is to have three sensors

Which can also fail:

In 2008, on a customer-acceptance flight of an Airbus A320, two of the angle-of-attack sensors froze and those two sensors then outvoted the third. When the pilots went to demonstrate the stall-prevention system, they were not aware of the malfunctioning sensors. The plane crashed, killing the seven people on board.

The same problem arose again on a 2014 Airbus A321 Lufthansa flight leaving Spain. Eight minutes after takeoff, two of the angle-of-attack sensors froze at the same pitch. This time, after a drop in altitude, the pilots were able to regain control and complete the flight. [1]

I don't think the fundamental problem with MCAS was the number of sensors, but that it was too difficult for the pilots to override MCAS when it faulted.

1. https://www.seattletimes.com/business/boeing-aerospace/a-lac...