Data from the jetliner that crashed into the Java Sea last month shows the pilots fought to save the plane almost from the moment it took off, as the Boeing 737’s nose was repeatedly forced down, apparently by an automatic system receiving incorrect sensor readings.
The information from the flight data recorder, contained in a preliminary report prepared by Indonesian crash investigators and scheduled to be released Wednesday, documents a fatal tug-of-war between man and machine, with the plane’s nose forced dangerously downward more than two dozen times during the 11-minute flight. The pilots managed to pull the nose back up over and over until finally losing control, leaving the plane, Lion Air Flight 610, to plummet into the ocean at 450 miles per hour, killing all 189 people on board.
The data from the so-called black box is consistent with the theory that investigators have been most focused on: that a computerized system Boeing installed on its latest generation of 737 to prevent the plane’s nose from getting too high and causing a stall instead forced the nose down because of incorrect information it was receiving from sensors on the fuselage.
In the aftermath of the crash, pilots have expressed concern that they had not been fully informed about the new Boeing system — known as the maneuvering characteristics augmentation system, or M.C.A.S. — and how it would require them to respond differently in case of the type of emergency encountered by the Lion Air crew.
“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 international center for air transportation at the Massachusetts Institute of Technology.
Boeing has said that the proper steps for pulling out of an incorrect activation of the system were already in flight manuals, so there was no need to detail this specific system in the new 737 jet. In a statement on Tuesday, Boeing said it could not discuss the crash while it is under investigation but reiterated that “the appropriate flight crew response to uncommanded trim, regardless of cause, is contained in existing procedures.”
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