Investigators are still on working to find out exactly what is wrong with Lion Air in Indonesia on Monday, October 29, when Boeing 737 MAKS fell into the Java Sea, killing all 189 people on board.
But the initial findings highlighted the probable problem of the sensors, and that was enough for Boeing to issue safety warnings to all airlines that run these planes, telling pilots to worry about dealing with confusing reading or improper actions from the flight control computer, which it could cause the aircraft to dive, hard. And now the FAA says it throws its weight behind Boeing's advisory work, to oblige him to adhere to US airlines.
In a statement, Boeing said: "The National Traffic Safety Board in Indonesia has indicated that the Lion Air 610 has experienced a wrong entry from one of its AOA (Angle of Attack) sensors."
The angle of attack sensor is what computer and aircraft pilots use to find out how much lift a wing generates while cutting through the air. If the angle of attack is too steep, the raising starts to decrease, possibly creating an aerodynamic stand, where there is not enough lift to keep the plane above the head.
The way this can be countered is to straighten the plane's nose slightly down, which security systems will automatically operate, as well as aggressively and loudly shake the yoke control as a warning. But if the readings are incorrect or inconsistent, both automation and people can be confused to go further and further as they try to find out what is happening and what to do about it, causing a sharp nose. The situation can quickly escalate. "These guys really could have their hands full of airplanes," says Les Westbrook, professor of aeronautics at the Embri-Riddle Aeronautics University and a qualified pilot at Boeing 727, an earlier commercial aircraft called Boeing.
The plane Lion Air crashed into the sea less than half an hour after the flight. Pilots requested permission to return to Jakarta Airport, but instead of sailing on the plane, and maybe it was at a speed of 600 miles an hour when it hit the water.
Each issue with 737 MAKS is troubling, as it is proven as a popular model around the world for Boeing, which delivered 219 generations of 737 narrow reactors and sat on orders of more than 4,700, making it the fastest-selling aircraft in Boeing's history. It is an upgrade to the previous 737s, with more efficient engines and distinctive wings for better aerodynamics. Boing started shipping in May 2017. The largest buyers in the US so far are Southwest and American. At the international level, Air Canada, Lion and Norvegian have them in their fleet, as well as several Chinese regional airline companies.
Boing did not respond to a request to clarify whether this safety warning affects only a particular model, MAKS-8, that Lion Air is flying or if it affects MAKS-7 to MAKS-10, which are of different lengths.
So far, the newsletter does not call for inspection or replacement of sensors or computers. On the contrary, trying to make sure they were not dismissed, Boeing repeated what the flight crew would do if they got the wrong readings. According to the announcement, it "directs operators to the existing flight crew procedures to face the circumstances in which the input from the AOA sensor is wrong."
They effectively say, "Come back, get dressed again, remember what to do." On the most basic, correct procedures mean ignoring what instruments and warnings are saying and resetting the aircraft to a stable situation. "The ultimate answer is to set up a familiar point and adjust the power," says Westbrook. It should create a flight level and buy pilot time to understand which readings are real and which are the faults.
A crack investigation is ongoing and can reveal other problems of compounding except sensors. But the accent also highlights the issue of overconfidence with automated systems, and flying teams have minimal experience of handling manual flying, let alone casualties.
"For several years now, we are talking about the industry due to the degradation of pilot skills of manual flight," says Westbrook.
Aviation accidents are usually the result of one or more simple failures, followed by confusion among the crew, leading to a rapidly emerging situation. This happened when the 447 Air France crashed into the Atlantic on its way to Paris from Rio de Janeiro in 2009, killing 228. Airspeed sensors on the Airbus A330 froze, which led to the disconnection of the autopilot. The crew tried to fly manually, but she could not do it enough to offset the plane.
Airlines flying to the 737 MAKS, such as Norwegian carriers, say they do not take any aircraft, and aviation experts like Westbrook continue to emphasize that flying is a very safe mode of transport. "When I get into the plane, I'm free, I do not have to drive," he says, because the chances of a car accident are much higher. What Boeing investigators and accident researchers learn from the Lion Air strike should be returned to procedures, potentially including pilot training, which is still flying safely.
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