After a second deadly Boeing 737 Max 8 plane crash, the U.S. Federal Aviation Administration grounded the model last week.
Lion Air flight JT610 crashed in October, killing all of the passengers and crew on board. The pilots of the doomed Boeing jet reportedly scoured a handbook as they struggled to understand why the jet was lurching downwards just before they ran out of time and crashed.
The investigation into the October crash has now taken on new relevance after Ethiopian Airlines flight 302 went down in March near Bishoftu, also killing all passengers and crew on board. The Ethiopian Air crash experienced similar technical difficulties in the moments before the fatal crash.
While the physical recording from inside the Lion Air cockpit has not been made public, those with access to the recording have revealed its contents.
Sources say just two minutes into the flight, the first officer reported a "flight control problem" to air traffic control and said the pilots intended to maintain an altitude of 5,000 feet. Airspeed was reportedly mentioned on the cockpit voice recording but the first officer did not specify the problem with the plane in the recording.
An indicator showed a problem on the captain's display where he then asked the first officer to check the quick reference handbook, which contains checklists for abnormal events, one source said.
For nine or so minutes after, the pilots remained clam as they fought to climb as the plane's computer continued to fault and send them downward.
"They didn't seem to know the trim was moving down," another source told NBC News. "They thought only about airspeed and altitude. That was the only thing they talked about."
Just before the plane went down, the captain asked the first officer to fly while he checked the manual for a solution but the first officer was unable to control the plane.
The cause of the Lion Air crash has still not been determined but the November preliminary report mentioned Boeing's faulty sensor and the airline's maintenance and training.
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