Lion Air's admission that the doomed jet had a technical issue on a previous flight - and the captain's request to turn back to the airport minutes before its fatal dive - have raised questions about whether it had faults specific to one of the world's newest and most advanced commercial passenger planes.
Lion Air's first two attempts to address the airspeed indicator problem didn't work, and for the Boeing 737 MAX 8 plane's second-to-last flight on October 28, the angle of attack sensors were replaced, Tjahjono said.
A crucial sensor that is the subject of a Boeing safety bulletin was replaced on a Lion Air jet the day before it plunged into the Java Sea and possibly worsened other problems with the plane, Indonesian investigators have revealed.
An aerodynamic stall is when the wings of an aircraft can't produce enough lift and the plane starts to dive.
Boeing declined to comment. Such bulletins are routinely issued by aircraft and engine manufacturers, particularly in the wake of major events, and this one does little except to remind crews that the procedures for addressing this situation already exist. Based on the bulletin, it appears that the nose of the Lion Air aircraft pitched down during the climb-out phase in response to an erroneous input from the sensor.
The jet's airspeed indicator malfunctioned on its last four flights, and that problem was related to the sensor issue, said Soerjanto Tjahjono, chairman of Indonesia's National Transportation Safety Committee, on Wednesday.
737 MAX plane that crashed last week killing all 189 people on board. According to NBC News, the warning revolves around what pilots should do if the plane gives an erroneous reading from a sensor.
An Indonesian National Transportation Safety Commission (KNKT) official carries debris from the crashed Lion Air flight JT610 at Tanjung Priok port in Jakarta, November 4, 2018.
The second black box on the plane, the cockpit voice recorder, has not yet been found.
It was not immediately clear whether the reported problem stemmed from a mechanical or maintenance issue, nor whether US authorities would order any checks.
The U.S. Federal Aviation Administration said Wednesday it would require airlines to follow Boeing's newly released safety bulletin, reminding pilots how to handle erroneous data from the sensor.
"If the nose is trimmed down on an aircraft, it becomes hard for the crew to hold it", said a person briefed on Boeing's bulletin, SeattleTimes reported.
Pilots raise and lower the nose of Boeing jetliners by pushing and pulling on a yoke in the cockpit, which controls panels at the tail known as elevators. In the early days of the jet age, the pitch trim system was linked to several accidents.
"When there was a problem, the pilot would write it down and the mechanic would do (a repair).Then the plane would be declared airworthy". One of the pilots had trimmed the plane to push the nose down while trying to climb after aborting a landing, the report said.
All 181 passengers and eight crew members on board the aircraft died after it crashed into the Java Sea shortly after takeoff from Jakarta.