Originally Posted by
Bergerie1
Well there is a second AoA vane but the MCAS and stick shaker system only uses one at a time. The AoA vane being used swaps with the other AoA vane with Weight on Wheels. It appears both AoA vanes are fed to the ADIRUs so that is where the 'unreliable airspeed' comes from.
Boeing seemed to have expected that the crew would switch off the Stab Trim, if it repeatedly added nose down, even if it canceled on 'manual' trim button press, but then started again, and again and again. One crew did switch off stab trim, the accident crew did not.