The pilots of the doomed Lion Air airliner fought to save the plane almost from the moment it took off – as its nose was forced down apparently by an automatic system that received flawed sensor readings, according to a report.
The nose was forced down more than a dozen times during the 11-minute flight, but the pilots managed to pull it up repeatedly until they finally lost control of the Boeing 737 Max 8, which slammed into the Java Sea on Oct. 29, killing all 189 people aboard, The New York Times reported.
Information from the flight data recorder confirmed investigators’ theory that the maneuvering characteristics augmentation system, or MCAS, installed on Boeing’s newest 737 was to blame, the paper reported, citing a preliminary report from Indonesian authorities.
The MCAS, which is meant to prevent the nose from rising too sharply, causing the plane to stall, instead forced it down due to bad information sent from sensors along the fuselage, findings show.
“The pilots fought continuously until the end of the flight,” said Capt. Nurcahyo Utomo, chief of the air accident subcommittee of the Indonesian National Transportation Safety Committee, which is leading the probe.
R. John Hansman Jr., a professor of aeronautics and astronautics at the Massachusetts Institute of Technology, told The Times: “It’s all consistent with the hypothesis of this problem with the MCAS system.”
Earlier this month, Boeing and the Federal Aviation Administration issued a safety alert, saying a sensor issue could cause the 737 Max 8 to nose dive and crash because of incorrect input from the sensors of the “angle of attack,” the angle of the plane or its wings relative to wind.
After the crash, pilots have complained that they had not been fully informed about the MCAS — and how they would have to respond differently in case of the type of emergency that downed Flight 610.
Boeing has said the proper procedures for responding to an incorrect MCAS activation were already explained in flight manuals, so there was no need to address this specific system in the new 737 Max 8.
In a statement Tuesday, the company said it could not discuss the crash while it remains under investigation but noted again that “the appropriate flight crew response to uncommanded trim, regardless of cause, is contained in existing procedures,” The Times reported.
Pilots also have pointed out a potentially critical difference between the system on the new 737s and the older models.
In the older versions, flight crews said they could help address the problem of the nose being forced down improperly — a situation known as “runaway stabilizer trim” — by pulling back on the yoke in front of them.
In the Max version, that measure does not work, pilots said, citing information they have received since the crash, according to the newspaper.
The pilots on Flight 610 apparently pulled back on their control columns forcefully to no avail, according to the information from the flight data recorder.
One of the angle-of-attack sensors on the fateful flight was replaced before the plane’s penultimate flight after having transmitted some incorrect angle and speed data, investigators have said.
Investigators have yet to recover the cockpit voice recorder, which could provide vital information about the pilots’ actions and whether they followed correct procedures to deal with the emergency.
The captain had handed the controls over to the first officer just before the plane plummeted on its flight from Jakarta to Pangkal Pinang.