Thomas Maresca

Special to USA TODAY

The Lion Air jet that crashed into the Java Sea last month, killing all 189 on board, was “not airworthy,” Indonesian investigators said Wednesday.

A preliminary report from Indonesia’s National Transportation Safety Committee (KNKT) based on flight recorder data found that pilots struggled to control the plane as its automatic anti-stall system repeatedly pulled the plane’s nose down on October 29.

The jet, a new Boeing 737 MAX 8, had experienced similar problems on a flight the night before but pilots on that flight had turned off the automatic safety feature.

“This is the basis of our recommendation to Lion Air. In our view, the plane was not airworthy,” Nurcahyo Utomo, head of the transportation safety committee told reporters in Jakarta on Wednesday.

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The committee’s report focused on the airline’s maintenance practices and pilot training as well as the problems with the anti-stall system but did not pinpoint a cause for the crash.

The aircraft had recorded problems measuring airspeed and altitude on four flights in the three days prior to the doomed Flight 610, the report noted. Two days prior to the flight, an “angle of attack” sensor that measures air flow over the plane’s wings was replaced.

The anti-stall system, known as the Maneuvering Characteristics Augmentation System or MCAS, appeared to be responding to faulty readings from the angle of attack sensors on the doomed flight.

According to the flight recorder data, the pilots of Flight 610 first encountered the problem just minutes after takeoff, and continued to manually override the automatic control more than two dozen times. Contact was lost with the plane just 13 minutes after it took off from the capital, Jakarta, en route to the city of Pangkal Pinang.

The pilot had requested a return to the airport before the plane lost contact. It is unclear why the crew did not turn off the MCAS feature. Officials are still searching for the cockpit voice recorder which will provide further answers.

The Indonesian National Transportation Safety Committee and the Allied Pilots Association, a U.S. pilots’ group, have said that the anti-stall feature was not adequately documented in the operation manual for the Boeing 737 MAX.

In a statement on the preliminary report, aircraft manufacturer Boeing said it was “deeply saddened by the loss of Lion Air Flight 610” but defended the safety of the 737 MAX.

“As our customers and their passengers continue to fly the 737 MAX to hundreds of destinations around the world every day, they have our assurance that the 737 MAX is as safe as any airplane that has ever flown the skies,” the statement said.

Lion Air, which was founded in 1999, has had some safety and maintenance issues in the past and was banned from flying into European airspace from 2007 until 2016. The airline had a crash in 2004 that killed 25 people and has had a number of other incidents, including a crash landing in the sea near Bali in which all 108 passengers survived.