The aircraft used for Lion Air flight JT610, which crashed into the Java Sea during a flight to Pangkalpinang, Bangka Belitung Islands, from Jakarta on October 29 was in bad condition during previous flights, the National Transportation Safety Committee (KNKT) has revealed.
That "angle of attack" sensor gave faulty readings throughout the short flight, triggering a system that automatically pointed the plane's nose down more than two dozen times, with pilots responding by manually fighting to correct the pitch.
Investigators said Lion Air kept putting the plane back into service despite repeatedly failing to fix a problem with the airspeed indicator, including on its second-last flight from Bali to Jakarta.
"In our view, the plane was not airworthy", he told a news conference in Jakarta.
Boeing chief executive Dennis Muilenburg said earlier this month that Boeing provides "all of the information that's needed to safely fly our airplanes" but the jet's manual and training methods have come under scrutiny after the crash. The airliner was just a few months old.
Boeing was accused by some pilots in the U.S. of not properly documenting the nature of changes made to the MCAS system in the 737 MAX, an aircraft that only entered service in 2017.
"It's all consistent with the hypothesis of this problem with the M.C.A.S. system", said R. John Hansman Jr., a professor of aeronautics and astronautics and director of the global centre for air transportation at the Massachusetts Institute of Technology.
The pilots of that flight reported problems to Lion Air's maintenance team, which checked the jet and cleared it for take-off on the doomed flight the next morning. In fact, before the penultimate flight, engineers had replaced one of the angle-of-attack sensors.
Utomo said the agency had not determined if the anti-stall system, which was not explained to pilots in manuals, was a contributing factor.
Members of the National Transportation Safety Committee lift a box containing the flight data recorder from a crashed Lion Air jet
However they did note that the aircraft was still in service despite a fault with the airspeed indicator. The information can be critical in preventing an aircraft from stalling.
The preliminary report did not assign blame, but did list new safety recommendations to Lion Air - "on top of earlier recommendations about the flight manual that have already been implemented by Boeing", Reuters reports.
'The pilots fought continuously until the end of the flight, ' said Captain Nurcahyo Utomo, the air accident investigator who is leading the probe.
The plane experienced technical problems in four earlier flights.
Lemme said he was troubled that there weren't easy checks to see if sensor information was correct, that the crew of the fatal flight apparently wasn't warned about the problems on previous flights and that the Lion Air jet wasn't fully repaired after those flights. The findings were part of a preliminary report prepared by investigators looking into what caused a Boeing 737 Max passenger jet to crash minutes after takeoff on October 29.
The pilot should have discontinued the flight, the National Transport Safety Committee found.
The plane that crashed is the newest type of Boeing's popular 737 jetliner.
The report is the most detailed look yet from authorities at the 11 minutes the plane was in the air.
Crash investigators will attempt to reconstruct the crash at a Boeing facility in Chicago. Because the MAX aircraft have heavier engines, the center of gravity is biased more forward than on previous models and MCAS is meant to improve pitch feel and provide stall protection.
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