Boeing “withheld information” on 737 MAX

Boeing failed to tell airline pilots about features of a new flight-control system suspected of playing a role in the fatal crash of an Indonesian 737 MAX plane, according to pilots who fly the jet in the U.S.


In Oct 29 Lion Air crash that killed 189 people in Indonesia, investigators have determined that AOA sensor was feeding bad data to jet’s flight computer, repeatedly activating MCAS when there was no risk of stall


Boeing 737 MAX: Incorporates Manoeuvring Characteristics Augmentation System (MCAS) – anti-stall feature introduced due to heavier engines, which changed aerodynamics of jet


Engines: Two CFM Leap-1B turbofans


HOW MCAS WORKS

Level flight: Normal angle of attack (AOA) – angle at which airflow hits aircraft

Aircraft trajectory

AOA sensor
Winglet aligns itself with airflow

AIR FLOW

Nose-up flight
High AOA puts aircraft at risk of stalling. MCAS automatically triggered, moving horizontal
stabiliser trim anticlockwise to push jet’s nose down

Longitudinal axis of aircraft

Angle of attack

Aircraft trajectory

AIR FLOW

Measured angle of attack

System activates only when plane is being flown manually, in flaps-up flight, and typically during steep turns


Sources: AP, JAO Aero Media LLC, New York Times, Seattle Times 
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