"In our view, the plane was not airworthy", he said on Wednesday.
As soon as the October 28 flight from Bali to Jakarta lifted off, a device known as a "stick shaker" - which is created to alert pilots to an imminent aerodynamic stall - activated with its unmistakable vibrations on the control column and loud thumping noise.
KNKT investigator Nurcahyo Utomo on Wednesday said the safety committee had not yet determined if the system was a contributing factor.
"Had they fixed the airplane, we would not have had the accident", he said.
Boeing said that "the appropriate procedure to address unintended horizontal stabiliser movement" was contained in the relevant flight manuals. "A lot" could be attained by investigators from the voice recorder, Utomo said.
The aircraft maintenance log shows that since Oct 26, there had been six reports of problems, including faulty sensor readings.
Black box data showed the plane had an airspeed indicator issue on multiple earlier flights, investigators said. Pilots even asked air traffic controllers to tell them how fast and high they were flying.
Investigators are expected to restrict their report to factual details from the jet's flight data recorder, which contains 69 hours of information from its last 19 flights.
The report discussed Lion Air's maintenance practices and an anti-stall system in the aircraft; investigators said it was "too early" to identify a firm cause for the crash.
Information provided to American Airlines from Boeing since the crash, Tajer said, "specifically says that pulling back on the control column in the Max will not stop the runaway if MCAS is triggered".
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On that next-to-last flight, the angle discrepancy between the two sensors was 20 degrees, according to officials from Indonesia's National Transportation Safety Committee.
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. On the flight from Bali to Jakarta, the flight crew shut off the motor that was trying to push down the nose.
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. While maintenance workers checked various sensors, they didn't work on the angle-of-attack system, which would have been an obvious item to examine because it had been replaced in work on October 27 and could have been related to the plane's failures.
"Data from the flight data recorder summarized in the report also makes clear that, as on the previous flight, the airplane experienced automatic nose down trim, " the manufacturer said. "This condition is considered as un-airworthy condition" and the flight should have been "discontinued".
Boeing, in a statement released after the report's publication, said the company appreciates KNKT's efforts to investigate the cause of the accident, and is "taking every measure to fully understand all aspects of this accident".
The night before the accident, pilots on the same plane continued to their destination despite significant malfunctions that investigators now say made the plane "unairworthy".
KNKT also acknowledged actions to improve safety had been taken by Boeing, Lion Air, the U.S. Federal Aviation Administration and Indonesia's Directorate General of Civil Aviation.
Lion Air sent a reminder to its pilots one day after the crash that they should "check any defect" from previous flights and "be ready for any abnormal or emergency conditions by having Memory Items and maneuvers reviewed".
Lion Air President Director Edward Sirait bristled at some of the preliminary report's findings.
Indonesian investigators expect to fly to the USA later this week to gather more information about the Boeing aircraft and its components, including discussing the MCAS safety feature with Boeing engineers to understand how it may have contributed to the accident, Utomo said.