Black box data shows pilots fought control system in Indonesia crash

Flight data shows bad sensor data kept forcing nose of aircraft down.

Enlarge / Cpt Nurcahyo Utomo (head of Flight Mode Indonesian Safety Transportation Committee) during the press conference, in Jakarta, Indonesia, on November 28, 2018. (credit: Donal Husni/NurPhoto via Getty Images)

More evidence supporting the theory that faulty sensor data caused the crash of a Lion Air Boeing 737 MAX in October has emerged from the aircraft's flight data recorder. A report released on November 28 by Indonesian crash investigators shows that the pilots of Lion Air Flight 610 fought with the aircraft's maneuvering characteristics augmentation system, or MCAS, nearly from the moment the jet took off from Jakarta on October 29. And the aircraft had suffered from a similar problem on a flight from Bali to Jakarta the day before—a flight that was completed safely after the pilot shut down the 737 MAX's automatic anti-stall system.

"In our view, the plane was not airworthy" during its previous flight, said Nurcahyo Utomo, head of Indonesia’s national transport safety committee (KNKT), in a press conference today in Jakarta. Utomo faulted Lion Air's maintenance and safety culture in the crash, though a final finding on the cause of the crash is likely months away.

The 737 MAX lost in the crash had repeatedly had problems with its airspeed and angle of attack (AOA) sensors, both of which feed into the MCAS system. One of the AOA sensors on the lost aircraft was replaced after the problems on the flight from Bali to Jakarta the day before, and the plane was put back into service. The MCAS uses inputs from these sensors to detect if the aircraft is likely to stall—losing enough lift to stay airborne—and automatically adjust control surfaces. Those adjustments would push the nose of the aircraft down to increase the lift generated by the wings with a combination of improved air flow over the wings and increased airspeed.

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Indonesia 737 crash caused by “safety” feature change pilots weren’t told of

737 Max safety bulletin revealed changes to system that pilots never knew about.

Enlarge / SONY DSC (credit: PK-REN, Jakarta, Indonesia )

On November 6, Boeing issued an update to Boeing 737 MAX aircrews. The change, directed by the Federal Aviation Administration (FAA), came because Boeing had never provided guidance to pilots on what to do when part of an updated safety system malfunctioned—the very scenario that the pilots of Indonesia's Lion Air Flight 610 faced on October 29. Not knowing how to correct for the malfunction, the aircrew and their passengers were doomed. All aboard were lost as the aircraft crashed into the Java Sea.

First approved for commercial operation by the FAA on March 8, 2017, the MAX is just beginning to be delivered in large volumes. Lion Air was one of Boeing's primary foreign customers for the MAX, which is also flown by Southwest Airlines, American Airlines, and Air Canada. The Lion Air aircraft lost in the accident was virtually brand new, delivered by Boeing in August; this was the first accident involving an aircraft touted for its safety.

But Boeing never told pilots about one key new safety feature—an automated anti-stall system—or how to troubleshoot its failure. The manual update raised an outcry from pilots in the US.

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