Picture this: a new Boeing plane embarks on a routine flight. Takeoff is achieved without incident, and the plane is smoothly slicing through the sky, when all of a sudden, a faulty sensor starts feeding erroneous data to the plane’s flight-control system. All of a sudden, the pilots are scrambling to revive the plane’s engines, but unable to overcome the strength of Boeing’s automated systems, the plane’s nose tips toward the ground, and the plane crashes into a field, injuring 120 people and killing 9.
It’s worth reminding readers that there are some discrepancies between this story and investigators’ accounts of the circumstances surrounding the fatal crashes of Lion Air flight 610 and Ethiopian Airlines flight 302. That’s because the flight described above occurred roughly a decade earlier, in 2009, when Turkish Airlines flight 1951 crashed while attempting to land at Amsterdam’s Schiphol Airport.
Like the recent string of crashes, the Turkish Airlines plane was also a Boeing 737 (albeit an older iteration). But the aerospace company’s reaction to that crash was much different than its reaction to Lion Air flight 610. Instead of doing nothing, like it did after the crash in October, Boeing sprung into action and instituted what Bloomberg described as a “life-saving fix” across thousands of 737s: It changed the throttle systems to cede more control to pilots, precluding the possibility that an erroneous sensor could trigger a cascading tragedy.
But in light of reports exposing Boeing’s apparent confusion about basic safety features like cockpit alerts, which some analysts have warned might have helped pilots during the two recent mass-casualty crashes identify the problem sooner, others are questioning why Boeing didn’t move to act more quickly to take similar steps after the Lion Air crash?
Some have questioned why Boeing appeared to make some of the same mistakes with the MAX 737 8, like relying on one sensor to feed data to its MCAS anti-stall system, that it did on the earlier model before the Turkish Air crash. Though Boeing has insisted that it’s not yet clear whether MCAS contributed to the two fatal crashes – which combined killed more than 350 – the preliminary results from both investigations have settled on something different (though Boeing has apparently equivocated on this subject of exactly how much responsibility it’s willing to accept for the MCAS misfire).
Boeing ended up changing that throttle system to prevent one erroneous altitude reading from cascading into tragedy, changes the US Federal Aviation Administration subsequently made mandatory.
Yet when the Max debuted in 2017 with a new flight-control feature to help pilots avoid a stall, it was designed to react to only one of the plane’s two “angle of attack” sensors that measure the jet’s incline. That proved deadly when malfunctioning sensors on jets operated by Lion Air and Ethiopian Airlines automatically commanded the noses of the planes down over and over, even though the other sensor showed it wasn’t necessary.
“When I read that the planes had two angle-of-attack sensors, I couldn’t think of a reason why they wouldn’t use both,” said Robert Canfield, an aeronautical engineering professor and technical director of the Virginia Tech Airworthiness Center.
Unsurprisingly, Boeing insists that the Turkish Airlines crash shouldn’t be compared with the most recent crashes.
Boeing says the Max disasters shouldn’t be compared to the Turkish Airlines crash and no evidence has emerged to indicate that the altitude sensor, known as a radio altimeter, failed on the Lion Air or Ethiopian planes. “These incidents address fundamentally different system inputs and phases of flight,” Charles Bickers, a Boeing spokesman, said in an email.
“The 737 MAX was certified in accordance with the identical FAA requirements and processes that have governed certification of previous new airplanes and derivatives,” he said. The FAA signed off on the Max’s flight control feature, known as the Maneuvering Characteristics Augmentation System, or MCAS, he said.
“The FAA considered the final configuration and operating parameters of MCAS during Max certification, and concluded that it met all certification and regulatory requirements,” he said.
But one former FAA investigator went so far as to argue that the Turkish Airlines crash ‘foreshadowed’ the risks of relying on an automated system.
“Several parallels can be drawn,” said Jeffrey Guzzetti, the former director of the U.S. Federal Aviation Administration’s Accident Investigation Division. Guzzetti added that Boeing should have learned the ‘single sensor lesson’ – that is, the dangers of linking automated flight control systems to a single sensor – after Turkish Airlines. The Boeing 737 MAX 8 had two angle-of-attack sensors, but only one was linked to MCAS.
To be sure, not all experts agree on the parallels between MCAS and the earlier 737’s automated throttle system.
Not all experts agree that the Turkish Airlines crash – in which investigators also cited multiple pilot missteps – should have been a warning to Boeing when designing MCAS. While all three involve so-called single-point failures, that’s where the similarities end, said John Cox, president of consulting company Safety Operating Systems who participated in dozens of airline accident investigation as a pilot union representative.
“I don’t think it’s a fair comparison to say that Boeing should have known from the Turkish 1951 accident that they should’ve designed something different in MCAS,” Cox said.
In the 2009 crash, the erroneous altimeter data led to just one related failure: dialing back the jet’s throttle to idle prematurely. In the 737 Max crashes, faulty angle-of-attack data triggered airspeed and altitude warnings and caused the control yoke to shake violently, a sign that the plane could be approaching a stall, Cox said. That’s because the angle-of-attack readings factor in to those other sensors, he said.
“I think the only comparison you can make is that increasingly, airplanes are using more complex systems and that complexity on occasion can come up with unexpected results,” Cox said. “That’s true for Lion Air, Ethiopian Airlines and Turkish Airlines 1951, but to go beyond that I think is a stretch.”
This is only the latest in a string of embarrassing reports suggesting that Boeing’s negligence during the testing of the 737 MAX 8 – combined with lax oversight by FAA – contributed to both crashes. This could be hugely problematic for Boeing as it tries to convince the FAA that its new software update will be enough.
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