As speed and altitude readings started going haywire, a device known as a stick shaker activated on the left side of the cockpit, where the captain sits. The mechanism makes a loud noise and rattles a pilot's control column to warn of an impending aerodynamic stall.
But the Boeing Co. 737 Max wasn't about to stall. Instead, a computer was getting erroneous readings from a sensor mounted like a weather vane on the jet's nose. The malfunction triggered an anti-stall feature that forced the plane into a dive – the same system that was implicated in a crash less than five months before in Indonesia that killed 189 people.
To counteract it, the Ethiopian Airlines pilots responded with at least some of the steps that Boeing and the US Federal Aviation Administration recommended after the first accident. But amid a chorus of confusing alarms, they also made a critical oversight as they struggled for control, according to three pilots with experience in accident investigations: They left the engines set nearly to maximum.
"The thrust was full bore the whole way," said Roger Cox, a former accident investigator at the National Transportation Safety Board, who flew earlier models of the 737 while working as an airline pilot. "That is extremely curious."
Ethiopian Transport Minister Dagmawit Moges said in a press conference Thursday that the pilots followed proper procedures issued after the October crash of a Lion Air jet. She recommended that Boeing review its flight-control system. Aviation authorities should verify that the issues have been adequately addressed "before the release of the aircraft to operations," she said.
In an interview with CNN on Thursday, Ethiopian Airlines Chief Executive Officer Tewolde Gebremariam defended the pilots, saying the report proved the crew of EA 302 did more than what they were expected to do. "Today was a day for us to prove wrong all the speculators with false allegations," he said, adding that the airline will remain partners with Boeing.
Ethiopian safety officials stopped short of saying the plane needs a redesign. That helped boost Boeing's shares 2.9% to $395.86 at the close in New York, paring the decline since last month's crash to 6.3%.
Still, the two disasters in five months have pushed Boeing into one of the biggest crises in its century-long history. The crash in Ethiopia resulted in the worldwide grounding of the 737 Max, the revamped version of a plane model that accounts for a third of Boeing's operating profit. The accidents also prompted multiple investigations and reviews – including a criminal probe led by the US Justice Department – of how US regulators certified the flawed anti-stall system, known as MCAS.
The groundings are piling pressure on Boeing to come up with a fix that will keep pilots from having to make such complicated, split-second decisions to keep the 737 Max aloft. The company is redesigning its software and expects to complete the work within weeks. Among other changes, the update will keep the safety system from kicking in when only one of the sensors detects a stall.
"We at Boeing are sorry for the lives lost in the recent 737 Max accidents," CEO Dennis Muilenburg said in a video. The Chicago-based plane maker blamed the accident on "a chain of events" and acknowledged the sensor malfunction.