New York - The failure of an AOA (Angle of Attack) sensor caused two deadly Boeing 737 MAX crashes in 2019. An article from the New York Times claims that an earlier incident, which was never taken seriously, might have happened because of a similar reason.
Turkish Airlines Flight 1951 crashed during landing at Amsterdam Schiphol Airport, Netherlands, on 25 February 2009, resulting in the death of nine passengers and crew, including all three pilots.
The accident was never taken seriously by investigators said Sidney Dekker, an aviation safety expert who was commissioned by the Dutch Safety Board to analyze the crash.
Dr. Dekker’s study accused Boeing of trying to deflect attention from its own “design shortcomings” and other mistakes with “hardly credible” statements that admonished pilots to be more vigilant, according to a copy reviewed by The Times.
The study was never made public. The Dutch board backed away from plans to publish it, according to Dr. Dekker and another person with knowledge of its handling. A spokeswoman for the Dutch board said it was not common to publish expert studies and the decision on Dr. Dekker’s was made solely by the board.
"The Dutch Safety Board released the study after the New York Times published its investigation."
At the same time, the Dutch board deleted or amended findings in its own accident report about issues with the plane when the same American team weighed in. The board also inserted statements, some nearly verbatim and without attribution, written by the Americans, who said that certain pilot errors had not been “properly emphasized.”
The muted criticism of Boeing after the 2009 accident fits within a broader pattern, brought to light since the Max tragedies, of the company benefiting from a light-touch approach by safety officials.
References to Dr. Dekker’s findings in the final report were brief, not clearly written and not sufficiently highlighted, according to multiple aviation safety experts with experience in crash investigations who read both documents.
One of them, David Woods, a professor at Ohio State University who has served as a technical adviser to the Federal Aviation Administration, said the Turkish Airlines crash “should have woken everybody up.”
Some of the parallels between that accident and the more recent ones are particularly noteworthy. Boeing’s design decisions on both the MAX and the plane involved in the 2009 crash — the 737 NG, or Next Generation — allowed a powerful computer command to be triggered by a single faulty sensor, even though each plane was equipped with two sensors, as Bloomberg reported last year.
In the two MAX accidents, a sensor measuring the plane’s angle to the wind prompted a flight control computer to push its nose down after takeoff; on the Turkish Airlines flight, an altitude sensor caused a different computer to cut the plane’s speed just before landing.
Boeing had determined before 2009 that if the sensor malfunctioned, the crew would quickly recognize the problem and prevent the plane from stalling - much the same assumption about pilot behavior made with the MAX.
And as with the more recent crashes, Boeing had not included information in the NG operations manual that could have helped the pilots respond when the sensor failed.
Even a fix now proposed for the Max has similarities with the past: After the crash near Amsterdam, the F.A.A. required airlines to install a software update for the NG that compared data from the plane’s two sensors, rather than relying on just one. The software change Boeing has developed for the Max also compares data from two sensors.
Critically, in the case of the NG, Boeing had already developed the software fix well before the Turkish Airlines crash, including it on new planes starting in 2006 and offering it as an optional update on hundreds of other aircraft. But for some older jets, including the one that crashed near Amsterdam, the update wouldn’t work, and Boeing did not develop a compatible version until after the accident.
The Dutch investigators deemed it “remarkable” that Boeing left airlines without an option to obtain the safeguard for some older planes. But in reviewing the draft accident report, the Americans objected to the statement, according to the final version’s appendix, writing that a software modification had been unnecessary because “no unacceptable risk had been identified.” GE Aviation, which had bought the company that made the computers for the older jets, also suggested deleting or changing the sentence.
The Dutch board removed the statement but did criticize Boeing for not doing more to alert pilots about the sensor problem.
Dr. Woods, who was Dr. Dekker’s Ph.D. adviser, said the decision to exclude or underplay the study’s principal findings enabled Boeing and its American regulators to carry out “the narrowest possible changes.”
The problem with the single sensor, he said, should have dissuaded Boeing from using a similar design in the Max. Instead, “the issue got buried.”
Boeing declined to address detailed questions from The Times. In a statement, the company pointed to differences between the 2009 accident and the Max crashes. “These accidents involved fundamentally different system inputs and phases of flight,” the company said.
Asked about its involvement with the Dutch accident report, Boeing said it was “typical and critical to successful investigations for Boeing and other manufacturers to work collaboratively with the investigating authorities.”
Joe Sedor, the National Transportation Safety Board official who led the American team working on the Turkish Airlines investigation, said it was not unusual for investigating bodies to make changes to a report after receiving feedback, or for American safety officials to jointly submit their comments with Boeing.
Mr. Sedor is now overseeing the N.T.S.B.’s work on the MAX crashes. He acknowledged that reliance on a single sensor was a contributing factor in both cases but cautioned against focusing on it.
“Each of these accidents was complex and dynamic events with many contributing factors,” he said. “Boiling them down simply to the number of inputs ignores the many, many more issues that differentiate them.”
The F.A.A., in a statement, also emphasized the “unique set of circumstances” surrounding each accident. “Drawing broad connections between accidents involving different types of emergencies oversimplifies what is, by definition, a complex science,” it said.
The agency, also part of the American team in the Dutch investigation, declined to say whether the lessons from the Turkish Airlines crash factored into its decision to certify the Max — which was approved to fly in 2017 and became the fastest-selling plane in Boeing’s history.
But a senior F.A.A. official, who was not authorized to speak publicly, praised Dr. Dekker’s study and said it identified important issues that had not received enough public attention. The official pointed to the similarities — such as the reliance on a single sensor - between the Turkish Airlines crash and the Max accidents.
A spokeswoman for the Dutch board, Sara Vernooij, said it was common practice to amend draft reports in response to outside comments, but she declined to address the specific changes. Other companies and government bodies involved in the investigation, such as the French firm that made the sensors and that country’s aviation safety board, also submitted comments, but the American submission was the most extensive.
Via New York Times