Indonesian investigators said the cockpit recording from the crashed Lion Air jet showed the pilots searching a manual to try to find why the plane kept lurching downwards.
The details were revealed at a press conference, where an investigator said the recording captured a "panic" in the cockpit in the last 20 seconds of the flight.
They are looking into how a computer ordered the plane to dive in response to data from a faulty sensor and whether the pilots had enough training to respond to the emergency.
The investigation has taken on new urgency after a second 737 MAX 8 crash at Ethiopian Airlines last week killed 157 people and led to the global grounding of the model.

Netanyahu says Israel to decide which international forces in Gaza acceptable
Melissa develops to a Category 4 hurricane as Jamaica braces for impact
Two suspects in Louvre jewel heist case arrested in Paris
Russian attack on Kyiv kills three, injures 31
PKK announces withdrawal from Turkey
