Puzzled by description of AoA malfunction theory on recent Lion Air accident The theory for the recent Lion Air accident states that the AoA sensor malfunctioned and the airplane systems commanded nose down.
Boeing also stated this occurs when the autopilot is disabled. The implication is that the pilots had no input to disable nose down command.
Is this inference correct in the B737-Max?
The Operations Manual Bulletin put out by Boeing suggests that this is a trim runaway event.  Airspeed and altitude measurements are affected by the angle of attack of the airplane.  The indicated airspeed will be lower in a high angle of attack situation.  The accident airplane was reading a higher angle of attack than reality due to a malfunction of some kind.  The new avionics in the Boeing 737-MAX correct the airspeed measurement for angle of attack so airspeed was reading higher than what it should have been.  As a result the automatic trim, which is set to keep a constant airspeed, kept trying to lower the nose since the reported airspeed was too high.  

The 737-MAX Operations Manual Bulletin included procedures to disable the automatic trim.  This runaway trim event occurred during the 3 flights before the accident flight but maintenance was unable to fix the problem.  

More information on the accident can be found at the Aviation Herald.