On March
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 with 157 on board 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.
In a bid 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.
According to three pilots with experience in accident investigations, the pilots on the Ethiopian Airlines made a critical oversight amid the chorus of confusing alarms and the struggle to control the plane; they left the engines nearly set to maximum.
“The thrust was full bore the whole way, that is extremely curious.” 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.
In a press conference on Thursday, Ethiopian Transport Minister Dagmawit Moges said that the pilots followed proper procedures issued after the October crash of a Lion Air jet. Recommending 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.
Ethiopian safety officials stopped short of saying the plane needs a redesign. That helped boost Boeing’s shares 2.9 percent to $395.86 at the close in New York, paring the decline since last month’s crash to 6.3 percent.
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 U.S. 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. The update is expected to 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,” Chief Executive Officer Dennis Muilenburg said in a video. The Chicago-based planemaker blamed the accident on “a chain of events” and acknowledged the sensor malfunction.
According to pilots who reviewed a preliminary report issued Thursday by Ethiopia’s Aircraft Accident Investigation Bureau, at near-maximum thrust, the plane became more difficult to fly, multiplying the problems created by the flaw in the 737 Max’s software.
The high speed also made it impossible to recover in the final seconds when the plane’s nose pointed downward into their final, high-speed dive.
The Ethiopian report clearly showed that MCAS — the Maneuvering Characteristics Augmentation System, a safety measure added to the new plane to prevent it from dangerous stalls — had activated multiple times. That was similar to the Lion Air crash.
Sensors in the aircraft that report how high its nose is pointed relative to oncoming air varied by almost 60 degrees. One of the “angle-of-attack” gauges read 15.3 degrees, likely an accurate reading for a plane taking off.