The Lion Air jet that crashed into the Java Sea last month was not airworthy even on its second-to-last flight when pilots experienced similar problems to those on its doomed final journey, investigators say.
In a preliminary report, Indonesia's transport safety committee (KNKT) focused on the airline's maintenance practices and pilot training and a Boeing Co anti-stall system.
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Yet it did not give a cause for the crash that killed all 189 people on board.
The report unveiled fresh details of efforts by pilots to steady the 737 MAX jet as they reported a "flight control problem", including the captain's last words to air traffic control asking to be cleared to "five thou" or 5000 feet.
Contact with the jet was lost 13 minutes after it took off from Jakarta heading north to the tin-mining town of Pangkal Pinang.
Information retrieved from the flight data recorder showed the "stick shaker" vibrating the captain's controls warning of a stall throughout most of the flight.
The captain was using his controls to bring the airline's nose up but an automated anti-stall system was pushing it down.
Pilots flying the same plane a day earlier experienced a similar problem, en route from Denpasar to Jakarta, until they used switches to shut off the system, KNKT said.
"The flight from Denpasar to Jakarta experienced stick shaker activation during the take-off rotation and remained active throughout the flight," the report said.
"This condition is considered as un-airworthy condition" and the flight should have been "discontinued".
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.
After the crash, Lion Air instructed pilots to provide a "full comprehensive description" of technical defects to the engineering team, KNKT said.
In a statement, Boeing drew attention in detail to a list of airline maintenance actions set out in the report but stopped short of blaming ground workers or pilots for the accident.
The company, which has said procedures for preventing an anti-stall system activating by accident were already in place, said pilots of the previous flight used that drill but noted the report did not say if pilots of the doomed flight did so.
Reuters
