All 737s have two AoA sensors - they're used for several purposes, not just MCAS. Originally MCAS used only one of the two sensors, though it alternated which

All 737s have two AoA sensors - they're used for several purposes, not just MCAS. Originally MCAS used only one of the two sensors, though it alternated which one with each flight. The optional features were an AoA disagree indicator, and the AoA data itself being displayed on the cockpit displays. Having either optional feature didn't change the fact that MCAS only used one sensor.