The pilots of a Lion Air jet that crashed in Indonesia last year searched through a flight manual to understand why the aircraft was lurching downwards in the final minutes before it hit water, The New York Times reported on Wednesday based on audio from the cockpit voice recorder.

Bhavye Suneja, an Indian who was the captain, had handed over the controls to his co-pilot, Harvino, who began to pray as the aircraft’s nose went downward. Suneja then searched through the technical manual to identify the problem.

“I think he [Harvino] knew it was unrecoverable,” Nurcahyo Utomo, the head of the air accident subcommittee of the Indonesian National Transportation Safety Committee, told The New York Times. Utomo had listened to and described the contents of the cockpit voice recorder.

All 189 people on board Lion Air flight JT 610, from Denpasar to Jakarta, were killed when it crashed into the Java Sea. Investigators had said the Boeing 737 Max passenger jet had crashed minutes after takeoff on October 29.

A preliminary report based on the flight data recorder was released in November. The conversations between Suneja and Harvino, an experienced Indonesian pilot, was not included in the preliminary report as the cockpit voice recorder was retrieved from the ocean floor in January.

The findings in the preliminary report indicated that the pilots struggled to keep the plane steady as its nose tilted dangerously downward more than two dozen times.

A brief rattle could be heard on the voice recorder, which is proof that a device called a stick shaker was rattling to alert the pilots of a potential stall that could lead to a crash, said Ony Soerjo Wibowo, an air safety investigator. A stall can occur when a plane ascends sharply.

Officials of the Indonesian National Transportation Safety Committee, who listened to the cockpit voice recording, said the pilots discussed unreliable airspeed and altitude readings they were getting. However, the pilots did not seem to know about an anti-stall system called the MCAS or what was causing the aircraft to push downward.

US: Congress calls for hearing of Boeing

The United States Congress has called for a hearing of Boeing officials and federal regulators on March 27 in connection with the Lion Air crash last and an Ethiopian Airlines plane crash of March 10, in which 157 people died, AFP reported.

Senator Ted Cruz called for a hearing of the Commerce Subcommittee on Aviation and Space with three transportation officials, including the acting head of the Federal Aviation Administration. A second hearing will be held to question Boeing officials, pilots and others in the industry.

The US Transportation Department is investigating Boeing and the Federal Aviation Administration for how the rollout of the Boeing 737 Max 8 jets were handled, especially the a new flight system, the MCAS stall-prevention system. Both the planes involved in the crash were operating Boeing 737 Max 8 jets.

Meanwhile, the US Justice Department has issued multiple subpoenas as part of its investigation into Boeing’s Federal Aviation Administration certification and marketing of 737 Max planes, CNN reported quoting unidentified officials.