Investigators say faulty information from an external sensor led an automated safety feature, known as the Maneuvering Characteristics Augmentation System, or MCAS, to repeatedly force the plane’s nose down before the plane crashed in a field, killing all 157 people on board.
Under congressional questioning Wednesday, Elwell said the Ethiopian pilots, unlike the pilots in Indonesia, turned off the motors controlling the stabilizer that was forcing the airplane downward because of the MCAS problem. But Elwell said the Ethiopian pilots failed to control the plane’s speed and then, “about a minute before the end of the flight,” turned the motors back on. “Both of those things are unfortunate, obviously,” Elwell said.
Turning the motors back on allowed the MCAS system to push the plane downward again.
Elwell, a former American Airlines pilot, noted that he had “never looked at an accident where there weren’t three or four or five links in the chain, any one of which, if it hadn’t gone wrong, the plane would have survived.”
But Ethiopian Airlines, in a statement crafted with the help of the airline’s chief pilot, told The Washington Post that the claims were being made to “divert public attention” from problems with the flight control system.
The airline pointed to a host of problems with the jet as well as a lack of key training tools from Boeing.
The statement noted that Ethiopian Airlines was one of only a small number of airlines around the world that bought a full flight simulator for the 737 Max 8, which allowed pilots to become familiar with the system.
“However, it’s very unfortunate that the B737 Max 8 simulator was not configured to simulate the MCAS operation by the aircraft manufacturer,” the airline said.
The airline said it was a “major failure” that the MCAS feature was “designed to be automatically activated by a single source of information,” an external sensor known as an angle-of-attack vane.
Boeing this week said it has completed a software fix that will make the MCAS rely on two external sensors. The fix will also reduce the strength of the automated feature so it cannot overpower pilots. The company has also acknowledged that a cockpit indicator on Max jets, known as an “angle of attack” disagree alert, didn’t work on most planes because of a software problem.
The Ethiopian Airlines official noted that MCAS, which was meant to prevent stalling, was “not known by airlines and pilots until after the Lion Air accident,” which left 189 people dead in Indonesia under similar circumstances.
Elwell came under sharp questioning Wednesday over how the agency and Boeing had certified the plane as safe. The FAA has also been criticized for not requiring a clear description of the automated MCAS feature in documentation for pilots.
House Transportation Committee Chairman Peter A. DeFazio (D-Ore.) cited a Boeing engineer who was taped during a November meeting with a pilots’ union saying MCAS might be seen just once in a million miles, and that “we try not to overload the crews with information that’s unnecessary.”
“Do we really think that was unnecessary? It wasn’t in the manual, and they didn’t even know about it,” DeFazio told Elwell.
On Friday, an FAA spokesman declined to describe which FAA emergency procedures Elwell said the Ethiopian pilots had not followed.
The procedures called on pilots facing problems controlling the airplane in such circumstances to “disengage autopilot” and use to electric stabilizer motors, if necessary, to set a smooth course for the plane before turning off the automated system.
“We express our sincerest condolences to the victims, the crew, and their families,″ the FAA spokesman said.
Boeing said it could not comment on an ongoing accident investigation.