The pilots of the Lion Air Boeing 737 Max that crashed in Indonesia were searching a flight manual to try to find why the plane kept lurching downwards against their commands, according to reports of the cockpit voice recording.

The investigation into the crash, which killed all 189 people on board last October, has become even more significant for Boeing and airlines due to its suspected links with the Ethiopian Airlines disaster, where 157 died on the same model of plane.

The Ethiopian government and French accident investigators have said flight data shows clear similarities between the two 737 Max crashes.

According to sources who spoke to Reuters, the voice recordings from Lion Air – yet to be officially released – show that the captain asked the first officer to check the flight manual within minutes of takeoff as they struggled to control the aircraft.

The captain was at the controls of Lion Air flight JT610 when the 737 Max took off from Jakarta. Two minutes into the journey, the first officer reported a “flight control problem” to air traffic control. The sources said airspeed was mentioned on the cockpit voice recording, and that an indicator showed a problem on the captain’s display but not the first officer’s.

The pilots looked through the handbook containing checklists for abnormal events, as the jet incorrectly alerted pilots it was in a stall, pushing the nose down – an automated response built into the software as part of the maneuvering characteristics augmentation system (MCAS) anti-stall program in the 737 Max.

As the captain fought to climb, the computer continued to push the nose down. “They didn’t seem to know the trim was moving down,” the third source said. “They thought only about airspeed and altitude. That was the only thing they talked about.”

The sources told Reuters that the pilots remained calm for most of the flight. Near the end, the captain asked the first officer to fly while he checked the manual. The Indian-born captain, 31, was silent at the end, while the Indonesian first officer, 41, said “Allahu Akbar”, the Arabic expression meaning “God is greatest”.

The plane crashed shortly after, killing everyone on board.

Lion Air said all data and information had been given to investigators and declined to comment further.

Regulators around the world grounded the 737 Max model last week after a crash in Ethiopia, the second fatal disaster in five months. The black box recorders from Ethiopian Airlines flight 302 are being examined by French air accident investigators in Paris, who have yet to release an official report. However, the fact the pilot also reported flight control problems in the same new plane, which climbed erratically and crashed soon after takeoff, has left the safety of the plane in doubt.

More than 300 737 Max planes have been taken out of service and deliveries suspended for another 5,000 on order. Boeing has told airlines it expects to have new software ready by the end of the month.

Following the second fatal accident, US authorities are reviewing whether enough was done to ensure the plane was safe to fly. Federal prosecutors and regulators have opened an inquiry into the 737 Max’s development, with scrutiny mounting over how the US Federal Aviation Administration and Boeing certified the aircraft.

Questions have also been asked about the training of the Lion Air crew. Although pilots in the US have said the manufacturer did not highlight modifications to the plane’s behaviour, Boeing has said existing safety procedures would allow pilots to override the plane’s computer, should it erroneously attempt to force it down.

The preliminary report into the Lion Air crash showed that a different crew flying the same plane the previous evening had encountered the same problem but solved it after running through three checklists. However, they did not pass on that experience to the next crew, the report said.

According to a report from Bloomberg, disaster may have been averted on the previous flight only due to the presence of a third, off-duty pilot in the cockpit, a captain at Lion Air’s sister carrier, Batik Air, who knew how to solve the flight control problems.

The final report into the Lion Air crash could be released by July, Indonesian investigators said. The cause has not been determined, but the preliminary report highlighted Boeing’s MCAS system, faulty sensors, and the airline’s maintenance and training.