Trump Grounds All 737 Max Flights After Ethiopian Airlines Disaster

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President Trump has ordered the grounding of all 737 Max flights in the United States several days after an accident on Ethiopian Airlines Flight 302 resulted in the loss of all passengers and crew. Prior to his order, the FAA had steadfastly refused to take the plane out of service. More than a half-dozen nations and the EU have also ordered the 737 Max out of service.

The severity of this response is being driven by the highly unusual facts. Airplanes don’t crash. The 2015 car crash fatality rate according to the NHTSA was 1.13 fatalities per 100 million vehicle miles traveled. The equivalent rate for airlines is 0.0035. Airplane crashes are so rare, virtually every plane crash today is an edge case scenario. New planes crash even less than old planes — and the 737 Max 8 is a very new plane. The specific aircraft in question was less than four months old.

The reason everyone is grounding the 737 Max family is that this is now the second 737 Max 8 to fail, after the Lion Air crash in Singapore last November. In that case, a faulty AOA (angle-of-attack) sensor is believed to have caused the aircraft to activate its own anti-stall protection system, which put the nose of the aircraft into a dive. Boeing failed to notify pilots that this new anti-stall system existed on the Max 8 family, and the crew may have had no idea how to deactivate it.

We don’t know yet if the same problem occurred on Flight 302, but losing two of the same aircraft just months after they both debuted is an incredibly unusual occurrence. The possibility that the two losses are connected must be investigated. As my colleague David Cardinal has discussed, the de Haviland Comet is an excellent example of an aircraft that was introduced to rave reviews but later proved to have catastrophic defects. Issues can — and occasionally have — slipped through development.

In both the Lion Air case and the Ethiopian Airlines crash, there is evidence that the vehicle oscillated in the air. The graph below is from FlightRadar24 and contains the ground radar measurements on Flight 302.

ET302-0-Altitude-Values-Removed

The vertical speed line (green) shows whether the aircraft is gaining altitude or losing it. Each data point is 5-6 seconds apart, covering roughly 50 percent of the flight (three minutes, the aircraft crashed roughly six minutes after takeoff). And according to Ethiopian officials, one of the pilots on the 737 Max 8 reported “flight control problems” before the airplane crashed, but not any other issues that would point to malfunctions elsewhere with the aircraft.

Did Boeing Build a Catastrophic Flaw Into the 737 Max 8?

Last month, the New York Times released an extensive report on Lion Air Flight 610 and the 737 Max 8. This fourth-generation 737 was designed to keep the 51-year-old aircraft (the first 737 flew in 1968) competitive with more fuel-efficient versions of the Airbus A320. One of Boeing’s internal guidelines for the project was that any changes must be achievable without the need for any pilot retraining. But the engines Boeing wanted to use were larger than the old versions and had to be mounted higher and farther forward on the wings. These larger engines could cause the aircraft to destabilize under certain conditions, including high-banked turns at low speed.

To counter this, Boeing developed MCAS (Maneuvering Characteristics Augmentation System). MCAS is an additional software package intended to prevent stall under certain circumstances by pushing the plane’s nose downwards. Boeing didn’t try to hide the system — it’s disclosed in the plane repair manuals — but they didn’t disclose it to pilots or make any kind of effort to train crew members on its existence. Boeing’s argument throughout this process has been that the 737 Max 8 is a perfectly safe plane and that all existing crew training is sufficient to respond to any emergency situation they might encounter.

We now know that system has potential flaws. One issue highlighted in the NYT report last month is that MCAS only uses data from one AOA sensor when it calculates its own actions, even though there are two AOA sensors present. It isn’t known if Boeing or the FAA ever tested the 737 Max 8 with an AOA sensor deliberately sending bad data to the MCAS system.

There have been reports that Ethiopian Air Flight 302 “smoked and shuddered” before its plunge. If these prove true, it could point away from the MCAS system. It’s also possible that the MCAS system overrode any action the pilots were attempting to take to return the plane to proper control as a result of an engine or another component failure. Right now, we simply don’t know. Boeing is preparing a software update for the 737 Max 8, but that update was already in the works last month before Flight 302 fell out of the sky.

Boeing will fight tooth and nail to preserve the 737 Max 8. The aircraft is its most successful launch ever, with more than 5,100 on order and 350 delivered. Those orders could go up in smoke if the plane is found to have a fundamentally defective design. The fact that Boeing designed the failing system out of a desire to avoid the cost of retraining pilots wouldn’t go over well, either. But we don’t know why the plane crashed yet, and until we have at least some preliminary reports on that topic, we’d avoid a rush to judgment.

Feature image courtesy of Wikipedia

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