The pilots of a Boeing 737 MAX frantically scoured a manual before their plane crashed into the Java Sea in October, killing all 189 people on board.
Recordings from the cockpit of the Lion Air plane suggest that the pilots were struggling to understand why the jet was lurching downwards, but ran out of time before it hit the water.
Two minutes into the flight, the first officer reported a “flight control problem” to air traffic control and said that they intended to maintain an altitude of 5,000ft.
The captain was at the controls of the nearly new plane when it took off from Jakarta, and as an indicator showed a problem on his display, he asked the first officer to consult a handbook containing checklists for abnormal events.
For nine minutes, the jet warned pilots it was in a stall – meaning it could not generate lift and keep flying – and pushed the nose down in response.
Although the captain fought to continue climbing, the computer incorrectly sensed a stall and continued to push the nose down.
Investigators are examining how a computer ordered the plane to dive in response to data from a faulty sensor, and whether the pilots were adequately trained to respond to the emergency.
Previously, it emerged that a different crew on the same Boeing 737 MAX encountered similar problems a night before the crash, but had managed to solve the issue after running through three checklists.
However, the pilots in charge at the time of the crash had not been fully briefed about what happened.
Sources with knowledge of the cockpit voice recordings told the Reuters news agency that the pilots of Flight JT610 remained calm.
In the seconds leading up to the crash, the Indian-born captain was silent, while the Indonesian first officer said “Allahu Akbar” – or “God is greatest” – a common phrase used to express excitement, praise, distress or shock.
The investigation into the Lion Air disaster has taken on new relevance after the same type of Boeing plane was involved in another crash in Ethiopia, killing all 157 people on board.
Officials have said there are “clear similarities” between both crashes.
The cause of the Lion Air crash has not been determined, but the preliminary report mentioned the Boeing system, a faulty, recently replaced sensor and the airline’s maintenance and training.
Boeing 737 MAX planes have been grounded around the world in response to both crashes – totalling more than 300 aircraft. Deliveries of 5,000 more are on hold.
The company has vowed to make swift improvements to automatic flight software, but regulators in Europe and Canada have said that they want to verify the changes themselves instead of depending on US vetting.
Boeing is hoping to get 737 MAXs flying again, but the Chicago-based company has faced criticism for its handling of the incidents.
Chesley Sullenberger, a US pilot famed for landing a jet on the Hudson River – saving all 155 people on board – wrote on MarketWatch.com: “Our credibility as leaders in aviation is being damaged.
“Boeing and the Federal Aviation Administration have been found wanting in this ugly saga that began years ago but has come home to roost with two terrible fatal crashes, with no survivors, in less than five months, on a new aeroplane type, the Boeing 737 Max 8, something that is unprecedented in modern aviation history.”
Lion Air and Boeing have declined to make any further comment on the cockpit recordings because the investigation into the crash is ongoing.