The pilots of the Lion Air Boeing 737 MAX were searching in manuals for a solution to an apparent malfunction of a flight assistance system right until the aircraft plunged into water killing 189 people on board, Reuters reports.

The news agency provided additional details about the October 2018 crash based on three sources who are familiar with what was found on the airliner’s flight recorders.

A preliminary report into the incident was released in November, but the recorders were recovered only in January, and their transcripts were not made public.

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According to the story, the first officer and later the captain of the jet were going through a handbook for a solution to the abnormal aircraft behavior they were experiencing.

They continued doing it right until the Boeing plane plunged into the Java Sea. The first officer, who was manning the control column right before the crash, seemed to become desperate, as indicated by weaker inputs than those made by the captain.

“It is like a test where there are 100 questions and when the time is up you have only answered 75,” once source said. “So you panic. It is a time-out condition.”

The crew was also oblivious to the fact that the plane’s anti-stall system, which was misled by a faulty sensor into detecting a stall, was using the plane’s trim system to push its nose down. The system is usually used to keep the aircraft level and the system is supposed to prevent the crew from lifting the nose too much.

“They didn’t seem to know the trim was moving down,” the same source said. “They thought only about airspeed and altitude. That was the only thing they talked about.”

The cause of the Lion Air flight crash is yet to be officially confirmed, but the prime suspect is the Manoeuvring Characteristics Augmentation System, or MCAS, which was developed for the 737 MAX. The US-based producer has since pushed a software upgrade which was supposed to change how much authority is given to the system in controlling the aircraft.

The suspected problem came under scrutiny again after yet another 737 MAX crash in Ethiopia, which, according to French air accident investigation agency BEA, showed “clear similarities” to the Lion Air disaster.

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In a separate report this week, Bloomberg revealed that the aircraft which crashed in October was saved by an off-duty pilot in a similar emergency on the previous day.

The incident was mentioned in a preliminary report by the Indian flight authority last November. However, this did not reveal the presence of a third pilot or details of how the disaster was averted.

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