Sensors were misfiring on the almost new Boeing Co.
The jet crashed following a request from the pilot for permission to turn back to the airport minutes after taking off from Jakarta.
Shortly after the catastrophe, the airline issued a notice to pilots urging them to be more proactive in reporting problems.
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.
Utomo said the agency had not determined if the anti-stall system, which was not explained to pilots in manuals, was a contributing factor. 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.
But they say these pilots may not have known what was going on in the cockpit. All it takes to prevent a crash is to block the hole at any point.
"In our view, the plane was not airworthy" during its previous flight, said Nurcahyo Utomo, head of Indonesia's national transport safety committee (KNKT), in a press conference today in Jakarta. The system was responding to faulty data, causing a nose dive.
While it will take months to sort out whether mechanics acted properly making repairs on the jet, sensors that measure speed and altitude were repeatedly failing on the four previous flights dating back to October 26, according to logs released in the report.
There appeared to be particularly serious problems with the anti-stall system. Similarly, an "angle of attack" sensor used to measure airspeed over the aircraft's wings was replaced a day before.
There were other issues pervading the aircraft, pertaining to its airspeed and altitude sensors, the report noted.
It is not clear whether the false data, which was on the pilot's side of the plane, was attributable to a problem with the sensor itself or with the computer that processes the sensor's information.
When the plane took off from Denpasar, however, a stick shaker created to warn of an impending aerodynamic stall activated and at 400ft the captain noted that an indicated airspeed (IAS) disagree warning was showing on the primary flight display.
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He said officials were receiving more requests from migrants wanting to return to their countries, but did not have a number. Most were dispirited after the US agents fired tear gas on the group of migrants trying to cross into the USA on Sunday.
Boeing has said that the procedure to correct an automatic nose-down pitch is in the plane's operating manual and pilots should have known about it.
"This is a report of facts", said Mr Nurcahyo.
The US and European Union flight bans have been lifted in recent years, but the industry is still wrestling with outdated infrastructure, accusations of cutting corners and heavy restrictions on hiring pilots and technicians from overseas to plug staff gaps.
"Airlines need to take paperwork seriously", Soejatman said. This plane had trouble before, this exact problem with this sensor.
Since the accident, Lion Air has beefed up its maintenance procedures for recurring problems, according to the report. They include bringing in more seasoned mechanics or conducting a test flight before a plane carries passengers.
New details of Flight JT610's final moments were also included in the report.
Although not mentioned in the report, the downward trim was due to to a flight control law, the Maneuvering Characteristics Augmentation System (MCAS), added to the 737 MAX to help pilots cope with a stall.
Lion Air President Director Edward Sirait bristled at some of the preliminary report's findings.
"You have to create a safety culture ... and in all the reports I've seen the owners of this airline (their culture was) just keep the show on the road, do what you're told, if you don't you'll get sacked".
"In our opinion, the plane was no longer airworthy and it should not have continued", he said. "Is this true? If it's like that, it seems that the report is finished". That will take time still - KNKT said it plans to finish a complete study within 12 months of the accident.
SCHAPER: Well, what Boeing is saying is that this was part of the safety manuals that they give pilots when they have a new model of the plane. That makes it more prone to failure, he said.
In the disaster's immediate aftermath, pilots for several airlines placed blame on Boeing for reportedly failing to provide information about the anti-stalling feature in its Max 8 and 9 aircraft.