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Crash Of Lion Air 737 MAX Raises Questions About Autopilot And Pilot Skills

Jeremy Bogaisky Forbes Staff

Aerospace & Defense Deputy editor for Industry; eyes on the skies

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AFP/Getty Images

The FAA issued an emergency airworthiness directive Wednesday to airlines operating the new Boeing 737 MAX, calling on them to better instruct pilots on how to deal with a potential faulty reading from a key gauge, an angle of attack sensor, that's supposed to help keep planes from falling out of the sky. The directive follows the discovery that the sensor was malfunctioning on a Lion Air 737 MAX that plunged into the sea off Indonesia on Oct. 29, killing all 189 aboard.

The accident and the FAA warning, which comes after Boeing issued a similar bulletin, may be less an indication that there’s anything wrong with the new version of Boeing’s top-selling plane than a sign of how increasingly automated flight systems are eroding pilot skills, says Keith Mackey, a Florida-based safety consultant who’s a former airline pilot and accident investigator.
To put it simply, says Mackey, the FAA’s directive tells pilots to turn off the plane's autopilot system, and if necessary the pitch trim system too, and fly the plane yourself.
“It’s unfortunate that they even have to write something like this,” says Mackey. “It should be understood.”

The angle of attack sensor is a vane on the wing that gauges air flow to determine if the wing is generating enough lift. That air flow can be disrupted if the plane slows down or goes into too steep a climb, putting the plane in danger of stalling. In that situation the 737 MAX has a pitch trim system that automatically pushes the nose down to prevent a stall. The FAA's and Boeing's bulletins explain to pilots how to disengage the system in the event that a faulty reading from the angle of attack sensor leads it to push the nose down.
Shortly after takeoff from Jakarta, the Lion Air plane’s pilots requested to return to the airport, but they never turned back, plunging into the water at high speed.
Based on the evidence available, says Mackey, the pilots may not have disengaged the autopilot or the trim system, which given the faulty angle of attack reading, may have lowered the nose and dived the plane into the water.

“The pilot should have recognized that I’m getting an erroneous indication on my airspeed,” he says. “It’s a nice day, you can look out the window and see that the airplane isn’t flying nose high.”
He sees the accident as indicative of two problems: the increasing use of autopilot is giving pilots less flight time to maintain basic skills, and a lower level of experience and training among pilots in the developing world.
Many airlines will require pilots shortly after takeoff to engage the autopilot, which in modern jets essentially manage the direction, speed and altitude of a plane based on instructions programmed by the pilot. Planes can also auto land at airports that have the necessary equipment.
“You get a lot of takeoffs and landings but no one gets much flying practice,” says Mackey. “They’re getting to be good computer programmers, they know which buttons to push and when to push them. When something begins to fail it becomes a puzzlement.”
In developing countries with small military and private aviation sectors, airlines tend to rely on Western schools for pilot training, putting many pilots at the controls of large aircraft with fewer flight hours, he says.
Those same factors limit the pool of trained mechanics. With air travel taking off in Asia, that can lead to systematic maintenance issues at growing airlines, says Mackey.
The Lion Air plane’s angle of attack sensor had registered incorrect airspeed readings on the four previous flights to the crash, according to the Indonesia National Transportation Safety Committee, and the sensor had been replaced the day before.
Mackey says it’s a red flag that the issue went unaddressed for so long.
Boeing has a lot riding on the 737 MAX: it has more than 4,500 orders on the books and has delivered 219. Lion Air was the launch customer for the 737 MAX 8, the variant of the plane that crashed, and the MAX 9.
Boeing's bulletin states that the angle of attack sensor can trigger the 737 MAX's automatic pitch trim system to push the nose down for as long as 10 seconds. If pilots manually pull the nose back up, the system can reengage after five seconds, pushing the nose down again, unless it's deactivated.
The 737 MAX is the only Boeing plane in which the angle of attack sensor triggers automated movements of the jet's tail, the aviation safety consultant John Cox told the Seattle Times.