A crashed Lion Air jet should have been grounded over a recurrent technical problem before its fatal journey, Indonesian authorities said Wednesday, as details from the new jet's flight data recorder suggested that pilots struggled to control its anti-stalling system.
The preliminary crash report from Indonesia's transport safety agency also took aim at the budget carrier's poor safety culture, but did not pinpoint a cause of the October 29 accident, which killed all 189 people on board.
A final report is not likely to be filed until next year.
The Boeing 737 MAX vanished from radar about 13 minutes after taking off from Jakarta, slamming into the Java Sea moments after pilots had asked to return to the capital.
Investigators said Lion Air kept putting the plane back into service despite repeatedly failing to fix a problem with the airspeed indicator, including on its second-last flight from Bali to Jakarta.
"The plane was no longer airworthy and it should not have kept flying," Nurcahyo Utomo, aviation head at the National Transport Safety Committee (NTSC), told reporters.
Lion Air's contested the preliminary result and said it was going to seek a written clarification from the NTSC.
"We think this statement is not true," President Director Edward Sirait said.
"The plane from Denpasar (Bali) was released and it was said (to be) airworthy according to documents and what the technicians have done."
"The plane was airworthy," he added.
The safety committee's findings will heighten concerns there were problems with key systems in one of the world's newest and most advanced commercial passenger planes.
"But we don't know yet whether it's a Boeing or airline issue," said aviation analyst Gerry Soejatman.
Investigators have previously said the doomed aircraft had problems with its airspeed indicator and angle of attack (AoA) sensors, prompting Boeing to issue a special bulletin telling operators what to do when they face the same situation.
The report confirmed that initial finding, saying the plane's data recorder detected an issue with the AoA.
It also said the plane's "stick shaker" -- which vibrates the aircraft's steering wheel-like control yoke to warn of a system malfunction -- was "activated and continued for most of the fight".
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 information can be critical in preventing an aircraft from stalling.
The doomed plane's flight data recorder showed that pilots had repeatedly tried to correct its nose from pointing down, possibly after erroneous data from AoA sensors was fed into a system that automatically adjusts some of its movements.
Black box data showed the plane also had an airspeed indicator issue on multiple earlier flights, said investigators, who have yet to locate the cockpit voice recorder on the sea floor.
Lion must take steps "to improve the safety culture" and bolster the quality of its flight logs, the transport agency said.
"Airlines need to take paperwork seriously," Soejatman said.
"That didn't cause the crash, but it can cause other problems in the environment they're working in."
Despite a dubious safety record and an avalanche of complaints over shoddy service, the budget carrier's parent Lion Air Group has captured half the domestic market in less than 20 years of operation to become Southeast Asia's biggest airline.
Indonesia's aviation safety record has improved since its airlines, including national carrier Garuda, were subject to years-long bans from US and European airspace for safety violations, although it has still recorded 40 fatal accidents over the past 15 years.
The report stopped short of making any recommendations to Boeing but the US planemaker has come under fire for possible glitches on the 737 MAX -- which entered service just last year.
The APA, a US airline pilots' union, said carriers and pilots had not been informed by Boeing of certain changes in the aircraft control system installed on the new MAX variants of the 737.
"I am really surprised if Boeing has not shared all the flight performance parameters with pilots, unions, and training organisations," University of Leeds aviation expert Stephen Wright told AFP, adding that "a deliberate omission would have serious legal ramifications".
In response to Wednesday's report, Boeing said: "(The company) is taking every measure to fully understand all aspects of this accident, working closely with the US National Transportation Safety Board as technical advisors to support the NTSC as the investigation continues."
Several relatives of the crash victims have already filed lawsuits against Boeing, including the family of a young doctor who was to have married his high school sweetheart this month.
Authorities have called off the grim task of identifying victims of the crash, with 125 passengers officially recognised after testing on human remains that filled some 200 body bags. - AFP