How the Boeing 737 Max safety system differs from others

By George Petras (USA TODAY)

A Boeing 737 Max 8 crashed in Ethiopia killing everyone on board. The crash of the Ethiopian Airlines plane marks the second deadliest accident involving a Boeing 737 in the past five months. So is there a problem with this particular model? USA TODAY

Note: A graphic on the Boeing flight system has been updated to show the correct position of an aircraft sensor.

Boeing’s 737 Max 8 jet and its onboard anti-stall system will undergo renewed scrutiny in the wake of Sunday’s Ethiopian Airline crash in which 157 people died.

Ethiopian Air’s Max 8 was identical to the one flown by Indonesia’s Lion Air Flight 610, which crashed Oct. 29 killing 189 passengers and crew.

The Max 8 uses a system called MCAS — Maneuvering Characteristics Augmentation System — which is designed to stabilize the aircraft in flight.

Boeing added MCAS after redesigning its 737 platform for the Max. The redesign changed the size and placement of the aircraft’s engines, which altered how the jet handled in flight.

The Max tended to raise its nose in flight, a movement called pitch. If an aircraft pitches too high, it risks stalling and crashing.

MCAS is designed to automatically reduce the pitch in manual flight without pilot input. The system is constantly fed data from two synchronized wing-like devices called Angle of Attack sensors, located on the plane’s nose.

If the AOA sensors detect the plane is pitching too high, the MCAS automatically adjusts the tail’s stabilizer — the horizontal part of the aircraft’s tail — to level out the plane.

However, if the AOA sensors feed faulty or contradictory data to the MCAS, the system can force the aircraft into a dive, according to a Boeing service bulletin issued Nov. 6.

Pilots can cut off the system manually, but its sudden activation can confuse pilots. Flight data recovered from the Lion Air crash showed pilots repeatedly tried to get the nose up.

Boeing delivered its first Max 8 in May 2017. About 350 Max jets have been delivered, with more than 5,000 orders pending.

Some airlines have grounded their 737 Max jets pending investigation.

SOURCES Associated Press; Boeing; Florida Institute of Technology; Federal Aviation Administration; theaircurrent.com; Embry-Riddle Aeronautical University; Reuters; USA TODAY research

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