Everyone who works at Boeing or takes an interest in the company’s long-term performance had best keep their seat belts fastened and their tray tables locked and in the upright position. The black box data from Ethiopian Airlines reportedly shows ‘similarities’ with the Lion Air crash. This has been rumored before, but we didn’t have the black box data on both aircraft to prove it.
The Boeing 737 Max 8’s stall-preventing MCAS (Maneuvering Characteristics Augmentation System) has been under scrutiny since Lion Air 610 crashed last year. We still advise against a rush to judgment. Even if the MCAS system is implicated in both crashes, it’s possible that other systems also failed, or that the MCAS failed for different reasons in this case. Fixing the problem will require a detailed understanding of what’s causing it in the first place, and we don’t yet have confirmation that the MCAS is responsible. Please keep this in mind.
A stall can occur when the nose of the plane is elevated, so a system that pushes the nose down could make sense — but pilots weren’t trained on how to recover the Boeing 737 Max from this event. Previous 737’s lacked this feature.
But the announcement of further similarities between the two crashes dovetails with some reporting from The Seattle Times. According to their investigation, Boeing was responsible for evaluating MCAS safety. Documentation provided to the FAA claims that the MCAS system can only adjust the horizontal tail on the plane by 0.6 degrees out of a maximum of five-degrees of nose-down movement. But that limit was later increased to 2.5-degrees of nose-down movement. Boeing didn’t communicate the change from 0.6-degrees to 2.5-degrees until after Lion Air.
“The FAA believed the airplane was designed to the 0.6 limit, and that’s what the foreign regulatory authorities thought, too,” said an FAA engineer to The Seattle Times. “It makes a difference in your assessment of the hazard involved.”
But that higher limit means MCAS causes a much larger amount of movement than the FAA was aware of. The pilots on Lion Air weren’t aware of anything, because they weren’t told MCAS existed. And here’s the next problem: The limit on tail adjustments only applies to an individual MCAS trigger.
In other words, if MCAS triggers, the pilot deactivates it, and then MCAS triggers again, it can shove the nose of the plane right back downwards. This could actually make the dive deeper if the MCAS triggered before the pilot had brought the aircraft back to its original neutral trim. It could reach a point where the stabilizer has been pushed to its end stop and is providing the maximum force possible to aim the plane’s nose at the ground. This effectively gave the MCAS “unlimited authority” according to Peter Lemme, a former Boeing flight control engineer who spoke to the Seattle Times. It had full authority to move the stabilizer the full amount,” Lemme said. “There was no need for that. Nobody should have agreed to giving it unlimited authority.”
Single Sensor Blues
In our previous article on the Flight 302 crash, we noted that the MCAS system relied on data provided by a single AOA sensor, without redundancy. If the MCAS system could only adjust the stabilizer by 0.6 degrees, an activation of the MCAS system would be classified as a “major failure,” meaning it could cause distress to people on the aircraft, but not death. Systems that fail as a “major failure” aren’t required to provide redundant solutions. (A major failure must have less than a 1 in 100,000 chance of occurring.)
A “hazardous” failure would occur if the 737 Max 8 activated MCAS while in a banked, descending spiral. In this instance, the MCAS system could cause serious or fatal injuries to a small group of passengers. A component with a risk of hazardous failure is supposed to have baked-in redundancies. The 737 Max 8 has two AOA sensors, but it only reads data from one of them and cannot compare the values it receives from two wings to determine if there’s a problem with the data.
The Seattle Times contains a good deal more information, including a discussion of pilot safety and training procedures and the actions taken by the Lion Air pilots. It’s good overall background reading.
Expect the impact of this loss to reverberate around the airline industry for years to come. In the aftermath of 9/11, the FAA found itself unable to keep up with the avalanche of recertification requests for basically every aspect of airline and airport safety. Rather than drastically increasing the size and scope of the FAA, Congress ordered the organization to begin relying on manufacturers for certification and safety checks.
If you’re thinking “Might it not be a bad idea to rely on manufacturers for security and safety checks?” well, you’d be right. With far too much work to do and too few hands to do it, the FAA acquiesced. Even within the FAA, there were those who believed the new program would be an improvement, by allowing the manufacturers, who were much more versed in the specific design and operation of their vehicles, to perform the testing. Critics of the system pointed to issues like the 787 Dreamliner fires as proof that this new era of cooperation between manufacturers and Boeing wasn’t improving the end result. FAA members have also said (anonymously) that they faced steep pressure from Boeing to approve the 737 Max 8. We already know Boeing was operating under a mandate to avoid any need for new pilot training on the revamped aircraft or risk being unprofitable compared to the Airbus A320neo.
We do not yet know exactly what caused these crashes, but the emerging picture isn’t complimentary. Boeing was under enormous pressure to bring the 737 Max 8 to market at the lowest price possible. It needed the new aircraft to beat the A320neo on fuel economy (it does). It pushed hard to have the plane approved for service. It did not train pilots on the MCAS system anywhere except Brazil, which insisted, claiming that pilots didn’t need more practice and that its existing policies and practices would be adequate for safe operation.
Even the cockpit displays and controls for the 737 Max 8 were also overhauled dramatically compared to earlier systems. I don’t have a simple way to showcase this in one shot, but there’s an entire website devoted to detailing the cockpit of the 737 flavors. Even a cursory check of the instrumentation panels reveals that things are very different. Control surfaces have changed.
It’s still entirely possible that details will emerge that clarify these two tragedies or explain their events in a way that doesn’t pin the blame on Boeing’s MCAS system. We still recommend avoiding a rush to judgment on this topic. The MCAS system could prove to be the sole factor or may have played a contributing role. It’s still at least technically possible that the problem could prove to be something else altogether, though at this point the chance that the MCAS isn’t involved in some fashion seems slim.