Ethiopia Crash Mystery Deepens: Pilots Initiated Boeing Protocol
(Bloomberg) -- New details in the probe into the Ethiopian 737 jetliner crash that indicate the pilots disabled a safety system driving down the nose -- yet still crashed -- only deepen the mystery of what happened, say pilots and former investigators.
The flight crew on the Ethiopian Airlines aircraft followed at least part of a protocol set by planemaker Boeing Co. to manually disable an automated anti-stall system as they tried to save the 737 Max jet, a person familiar with the situation said as Ethiopian authorities prepare to release a preliminary report on the accident Thursday.
However, the pilots didn’t perform another critical part of the checklist, said another person familiar with results of the Ethiopian investigation. Before cutting power to a motor operated by the Maneuvering Characteristics Augmentation System, they failed to adjust the plane so it wasn’t set to dive. That made it more difficult to fly the plane and may have hastened the fatal plunge that occurred later in the flight, said the person, who wasn’t authorized to speak and asked not to be identified.
The pilots later switched power back on to the so-called trim motor, said the person. That runs counter to the warning Boeing and the U.S. Federal Aviation Administration issued last November after the first crash of a 737 Max aircraft in Indonesia. The FAA’s emergency directive says switches controlling power to the trim system should be set to “CUTOUT and stay in the CUTOUT position for the remainder of the flight.”
MCAS engaged numerous times during the short flight, one of the people said. The software feature, which is programmed to push down a plane’s nose to help prevent aerodynamic stalls in some situations, is a focus of concern by regulators and lawmakers after 346 people died in crashes of Boeing’s newest version of the 737 flown by Ethiopian and Lion Air less than five months apart.
Investigators are also examining whether an angle-of-attack vane located near the nose of the Ethiopian plane malfunctioned or was damaged, perhaps by debris or a bird strike. An erroneous reading from a sensor, which measures the angle of the plane’s nose against oncoming wind, would activate the software.
The two disasters have rocked the credibility of Boeing as well as U.S. regulators who approved the new plane. Regulators around the world grounded the 737 Max, Boeing’s fastest-selling plane ever, before the U.S. FAA followed suit.
Boeing is working on a redesigned software package designed to limit MCAS’s movements and make it more reliable so that it won’t cause accidents in the future. The company needs several more weeks to finish and the update is subject to approval by U.S. regulators.
The Chicago-based manufacturer recommended against jumping to conclusions before the Ethiopian report is published.
“We urge caution against speculating and drawing conclusions on the findings prior to the release of the flight data and the preliminary report,” the company said in a statement Wednesday.
The data leaking out from the investigation raises many questions and still doesn’t provide a clear sense of why the plane crashed, said Jeffrey Guzzetti, the former director of the U.S. FAA’s Accident Investigation Division.
Following part of the procedure by turning off power to the motor driving the plane’s trim system makes sense, Guzzetti said. But turning it back on -- which wasn’t recommended by Boeing and aviation regulators -- wasn’t appropriate, he said.
“It just seems to me that the crew should have kept the thing off,” he said.
At the same time, the fact that the system flummoxed two Lion Air crews in Indonesia in October, including one that crashed shortly after takeoff, and possibly the Ethiopian pilots suggests that investigators will need to review whether the processes were too complex, Guzzetti said.
“There may be additional distractions and issues that are preventing crews from doing what they need to be doing,” he said.
The American Airlines pilots who flew Boeing simulators last week were surprised at how fast the plane’s trim system tried to push the nose down when MCAS activated, said Dennis Tajer, spokesman for the Allied Pilots Association, which represents pilots at the carrier.
“They were able to disconnect it and were able to use the manual trim, but they said it was a handful. This is a complex emergency,” he said. “To get my trust and confidence in the new software, I have to have some trust issues revisited.”
Once the Ethiopian pilots disengaged the trim system -- cutting power to its motor and preventing MCAS from acting -- they would have had to adjust the trim manually using wheels on either side of the cockpit. Trim moves the horizontal wing at the rear of the plane, adjusting how high or low the nose is pointed.
Those manual adjustments require coordination in the cockpit during a hectic time because one pilot may need to concentrate on flying the plane while the other moves the trim wheel by hand.
There are a range of reasons why pilots might not feel comfortable making those manual adjustments, said a U.S. 737 Max pilot. They may not have been trained adequately on how the trim wheel works, may not have used an arm on the wheel to make large adjustments or may not have coordinated well between each other, said the pilot, who wasn’t authorized to speak and asked not to be identified.
The Ethiopian aircraft was traveling at a relatively high speed, possibly making it tougher for pilots to manually shift the horizontal stabilizer and other flight-control surfaces.
“If you’re already going past the red line, the aerodynamic forces are a lot higher,” said Jon Weaks, a Southwest Airlines Co. 737 captain and president of the Southwest Airlines Pilots Association. “In theory, that could make it difficult. If you’re turning it manually, I don’t care how fast you crank on that thing, you can’t trim it as fast as an electric motor.”
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