"It's a stunning simple but deadly error," said Mary Schiavo, an aviation lawyer and former inspector general of the U.S. Transportation Department. "I can't even recall the number of accidents I've worked where the accident happened the first flight after maintenance. A reported problem, they supposedly fixed it, and then it goes down."
Boeing's bulletin said, "The Indonesian National Transportation Safety Committee has indicated that Lion Air Flight 610 experienced erroneous input from one of its AOA (Angle of Attack) sensors." A misreading in the sensor can cause a plane to dive suddenly.
Indonesian investigators said Wednesday that an AOA sensor on the jet was replaced the day before the doomed flight, on Oct. 28, when a pilot flying the same aircraft on a different route, from Bali to Jakarta, reported problems with it. The pilot on the crashed Lion Air flight had asked shortly after takeoff to return to the airport in Jakarta but lost contact with air traffic controllers afterward.
The Angle of Attack sensor, shown to reporters at a press conference in Jakarta on Wednesday, was manufactured by Minnesota-based Rosemount Aerospace Inc. The company did not respond to a request for comment.
Schiavo said it's clear from flight-tracking data that the pilots fought to keep the plane up.
"The pilots had a battle on their hands for a few minutes," she said. "They couldn't get above 5,000 feet at a time when they should have been over [10,000]. Something happened three to four minutes into the flight. They called to turn back to the airport, but they didn't call mayday, which means they didn't have time. They were fighting something."
In Jakarta, investigators showed reporters the AOA sensor that was removed from the aircraft. The small black cylinder contains a sensor that controls the angle between the wing and the air it is moving through. If the angle is too high as a plane climbs, that would cause a stall.
The Boeing 737 Max 8 jets are among the manufacturer's newest models and have been snapped up by airliners in booming aviation markets, including Indonesia and India.More than 200 are in service across the world, billed as the most advanced of the popular 737 jets - and capable of flying more than twice as far than the plane that debuted in 1967.
Indonesian authorities would provide Boeing with information from the pilot who flew with the problematic sensor so it could be shared with other airlines, said Nurcahyo Utomo, an investigator with the National Transportation Safety Committee.
Ony Suryo Wibowo, another investigator, said that it was too early to say what caused the crash. The full investigation could take a year.
The two Indonesian airlines that fly the Boeing 737 Max 8 planes, national carrier Garuda and Lion Air, both declined to comment on the bulletin. Indonesian officials say that all 11 such aircraft have been tested and declared safe to fly.
The 787 Max 8 is the second Boeing aircraft to experience serious technical problems soon after its introduction, leading some analysts to question whether Boeing may have overlooked quality concerns as it strives to meet rising global demand. Boeing has been working to increase production capacity at the Renton, Wash., factory where 737s are assembled.
The FAA grounded Boeing's entire 787 fleet in 2013 after lithium-ion batteries overheated and caught fire. The National Transportation Safety Board later faulted Boeing as well as its battery supplier, GS Yuasa, for its approach to safety and quality control.
The Seattle Times reported in August that Boeing's Renton factory has struggled to meet its production targets amid late deliveries from companies manufacturing its components. The company has sought to increase its production from 47 jets per month to 52 per month.
On Wednesday, Indonesian officials said the doomed flight would be re-created at Boeing facilities in Seattle to see what role the sensor may have played.
Experts have been puzzled about what could have caused the jet to go down in clear skies, unlike other major airplane disasters in which weather or older jets were major factors. The data from the flight recorder and Boeing's statement have provided the first clues, but rescuers are still searching for the device that records voices in the plane's cockpit. That recorder is expected to provide a clearer picture to investigators of the Lion Air flight's final moments.
"Boeing has now introduced two aircraft that have had significant problems," said Henry Harteveldt, an analyst with the consultancy Atmosphere Research Group. "What will have to be found is, is Boeing pushing itself too hard? Are the workers moving too fast to meet production deadlines?"
Still, Teal Group aerospace analyst Richard Aboulafia said the commercial passengers should not be nervous about getting on a 737 Max 8.
"We're going to learn from this just like we learned from the A330," he said, referring to a 2009 incident in which an Airbus A330 crashed off the coast of Brazil with 228 people on board due to electronics failures. "The big picture is the system keeps getting safer and safer, and it's still the safest form of transportation ever designed by humans," he said.
