Ethiopian Crash: Pilots Used Boeing Recommendations Inconsistently

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The pilots of an Ethiopian Airlines 737 MAX 8 that crashed on March 10 appear to have inconsistently applied Boeing recommendations to disable the MCAS stall-protection system. But they failed to recover the aircraft for reasons still unclear.

The Wall Street Journal, relying on sources who have seen the flight data recorder readout, reported that the pilots, upon experiencing uncommanded nose-down trim, used the 737’s stabilizer trim cutout switches. And while the 737 MAX 8 retains the manual trim wheels it has had from day one, it’s not known if they used these to re-trim the aircraft. The sources told the Journal that the pilots appeared to have reengaged the stabilizer trim cutout switches, which would have re-enabled the MCAS stall protection system.

The airline and Boeing insisted that the pilots of Ethiopian Airlines Flight 302 had been briefed on MCAS and potential abnormals after the Oct. 29, 2018, crash of a Lion Air MAX 8 in Indonesia. Investigators are focusing on the potential failure of the single angle-of-attack sensor that fed the MAX’s MCAS—Maneuvering Characteristics Augmentation System—an automatic background subsystem that feeds in nose-down trim when the aircraft is hand flown with flaps up at high angles of attack or high load factors. Both aircraft flew cyclic altitude and vertical speed excursions before crashing at high speed.

Boeing was widely criticized for delivering the MAX series without a specific recommendation for training or documentation on the MCAS system. The airplane maker is developing new software for MCAS, but it’s not expected to be available for several months.

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