NPR News:埃航空难初步调查报告公布 波音CEO承认飞行系统存在问题

We learned more today about what contributed to the fatal crash of an Ethiopian Airlines plane last month. Officials in Ethiopia released a preliminary report saying the Boeing 737 Max 8 unexpectedly and repeatedly went into a nosedive and that the pilots did exactly what Boeing said they should do under the circumstances, but they still couldn't regain control of the aircraft. The report does not answer all the questions about what went wrong and raises new questions about Boeing's response to a similar crash last fall in Indonesia. NPR's David Schaper reports.
DAVID SCHAPER, BYLINE: As Ethiopian Airlines flight 302 lifted off the ground at the Addis Ababa Airport on March 10 with 157 people on board, all appeared normal at first. But investigators say that changed rather quickly. One of 2 sensors measuring how the plane was moving through the air — called angle-of-attack sensors — started feeding the plane's computer systems erroneous data. And the plane started nosing down without the pilots telling it to. This was all very similar to what investigators say happened before a Lion Air 737 Max jet crashed in Indonesia last October, except investigators say those pilots didn't know what was happening. The Ethiopian pilots apparently did and took steps spelled out by Boeing after the Lion Air crash to try to regain control of the aircraft. Here's Ethiopian Transport Minister Dagmawit Moges.
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DAGMAWIT MOGES: The crew performed all the procedures repeatedly provided by the manufacturer but was not able to control the aircraft.
SCHAPER: What happened is this — as an automated system started nosing the plane down, the pilots tried to pull on the yoke to bring the plane back up.
SHAWN PRUCHNICKI: It's reflexive that they responded the way that they did, as it's very much ingrained in them.
SCHAPER: Shawn Pruchnicki is a former commercial airline pilot and crash investigator who now teaches aviation safety at Ohio State University.
PRUCHNICKI: What happened is they end up getting into a battle with the automation over control of the aircraft.

SCHAPER: The preliminary investigative report indicates that what the pilots did next was exactly what Boeing instructed them to do. They hit two switches to cut off electric power to the stabilizer that was moving the nose of the plane down, essentially disabling the flight control system. But doing that created another problem, says former Boeing flight control engineer Peter Lemme. They couldn't move the stabilizer to point the nose of the plane back up.
PETER LEMME: It left them in a position where they were just hanging on trying to hold the airplane at a reasonable level flight. They didn't have a lot of authority left over. So they were sort of stuck in a corner, and they weren't sure how to get out of that.
SCHAPER: This is something that Lemme says Boeing should have better communicated.
LEMME: Honestly, I feel like Boeing is one step behind the game all the way through here.
SCHAPER: Other experts agree. On NPR's Morning Edition, Peter Golz, former managing director of the National Transportation Safety Board, said Boeing had a responsibility to respond better after the first 737 Max 8 crash in Indonesia.
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PETER GOLZ: It was kind of an arrogant directive, I think, that Boeing put out after the accident which essentially said, read the manual and fly it and you should be OK. Well, apparently, you're not, and that is a big deal not only for Boeing, but for the FAA that signed off on it.
SCHAPER: In a statement, Boeing CEO Dennis Muilenburg says he cannot remember a more heart-wrenching time in his three-decade career at the company. He acknowledges that the MCAS flight control system on the 737 Max planes activated when it should not have in response to erroneous angle of attack information, and he says the company is working to fix the system. It's our responsibility to eliminate this risk, he says. We own it, and we know how to do it. David Schaper, NPR News.