Indonesian investigators said Wednesday that a faulty angle-of-attack indicator on a Lion Air Boeing 737 MAX 8 wasn't replaced or repaired prior to the October 29 crash into the Java Sea that killed all 189 people aboard.
All 189 people on board flight JT610 were killed when the plane crashed into the sea in what is, thus far, the worst airliner accident of 2018.
The new 737 MAX 8 faced struggles immediately during takeoff from Jakarta on October 28 that may have overwhelmed the pilots, according to black box data revealed in the Indonesia National Transportation Safety Commission's report.
An AOA sensor provides data about the angle at which air is passing over the wings and tells pilots how much lift a plane is getting.
"The plane was no longer airworthy and it should not have kept" flying, he added. It is flown or is on order by close to 40 airlines, with Lion Air in the process of receiving more than 200 of the jets.
"This condition is considered as unairworthy condition and the flight shall not be continued".
And it will press on with efforts to retrieve the cockpit voice recorder (CVR) in hopes of shedding light on what the pilots were saying as they fought to keep the plane up.
The Oct. 29 struggle against the automatic system, known as the Maneuvering Characteristics Augmentation System, or MCAS, was unsuccessful.
Pilots flying the same plane a day earlier had experienced a similar problem until they used switches to shut off the system, KNKT said in its statement today.
"The plane from Denpasar (Bali) was released and it was said (to be) airworthy, according to documents and what the technicians have done", said the airline's president director, Mr Edward Sirait, yesterday. This sequence continues for the rest of the flight.
The pilots of that flight reported problems to Lion Air's maintenance team, which checked the jet and cleared it for takeoff on the doomed flight JT-610 the next morning.
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"It's not something you ever want to have happen as a pilot", he said.
He said the agency had not yet determined if the anti-stall system, which was not explained to pilots in manuals, was a contributing factor.
"What they were focused on was keeping the airplane in the air", said Clint R. Balog, a pilot and aeronautics expert at Embry-Riddle Aeronautical University. "It is too early to conclude".
Boeing did not immediately respond to requests for comment.
Nearly immediately after takeoff, the report said the jet began to experience "stick shaker activation", which vibrates the pilot's controls. Before crashing, the pilot asked to return to the airport, but couldn't.
However, during flight JT610, the plane's automatic anti-stalling system repeatedly forced the plane's nose down, even when the plane was not stalling - possibly due to a faulty sensor.
Indonesian regulators were urged after previous accidents to improve their oversight of maintenance and pilot training.
Correcting the path of the plane would have required a multistep process, something that pilots and other aeronautics experts said may have been hard to remember and execute during a life-threatening emergency. The pilots were quickly locked in a deadly game of tug of war with a brand new Boeing 737 Max 8.
Black box data showed the plane also had an airspeed indicator issue on multiple earlier flights, investigators said. "At the moment I don't have the answer", said the NTSC's head of aviation, Capt. Nurcahyo Utomo.
Lion Air CEO Sirait said the airline would comply with KNKT's recommendations which included ensuring pilots made the proper decision on whether to continue a flight.
Investigators had earlier said that the plane had recurrent issues with airspeed and altitude readings.