The pilots of the Lion Boeing 737 Max, that crashed in Indonesia last year, were pouring over a flight manual looking for the cause of the problems they were experiencing before it crashed.
According to a source that spoke to Reuters, the voice recordings from Lion Air - which haven't officially been released - revealed that two minutes into the journey, the first officer reported a "flight control problem" to air traffic control.
In the voice recording the source said they heard airspeed mentioned and the plane's nose persisted in being pushed down despite the captain trying to get the plane to climb.
"They thought only about airspeed and altitude. That was the only thing they talked about," another source told Reuters.
The investigation into the crash that killed 189 people last October has become even more significant for Boeing due to its similarity to the Ethiopian Airlines disaster earlier this month where 157 people died in the same model of plane.