“The problems began around November 2016, when Forkner allegedly discovered that MCAS would turn on when the airframe was flying at Mach 0.2, a lower speed than previously determined. These speeds are often found during the most crucial parts of the flight: takeoff and landing.”
Mach 0.2 is less than 150 mph. Take-off and landing speeds are higher!
More critical is that turning off the autopilot turned ON MCAS. The very existence of MCAS was hidden from the pilots. So when they would have a problem, they would disengage the autopilot and it would get worse. There was nothing in the emergency manual that helped them know what they were fighting.
It’s inexcusable to completely hide such a critical system from the pilots.