By Jack Nicas and Zach Wichter , New York Times

In nearly 100 million flights by United States passenger airlines over the past decade, there has been a single fatality. Other than most landings and takeoffs, the planes have largely been flying themselves.

But the recent crashes of Boeing 737 Max 8 jets in Indonesia and Ethiopia have raised questions about the downside of all that automation.

Pilots now spend more time learning these automated systems than practicing hands-on flying, so newer pilots are less comfortable with taking manual control when the computer steers them wrong, according to interviews with a dozen pilots and pilot instructors at major airlines and aviation universities around the world.

"The automation in the aircraft, whether it's a Boeing or an Airbus, has lulled us into a sense of security and safety," said Kevin Hiatt, a former Delta Air Lines pilot who later ran flight safety for JetBlue. Pilots now rely on autopilot so often, "they become a systems operator rather than a stick-and-rudder pilot."

As a result, he said, "they may not exactly know or recognize quickly enough what is happening to the aircraft, and by the time they figure it out, it may be too late."

In October, a Lion Air jet crashed in Indonesia, killing 189 people. Investigators now think the pilots struggled to control the Boeing aircraft after its automated systems malfunctioned, in part because they didn't fully understand how the automation worked. The authorities are investigating what caused Sunday's crash of the same model jet in Ethiopia, in which 157 people died.

While automation has contributed to the airline industry's stellar safety record in recent years, it has also been a factor in many of the crashes that have still occurred around the world. A 2011 study by a federal task force found that in about 60 percent of 46 recent accidents, pilots had trouble manually flying the plane or handling the automated controls. Complicated automation systems can also confuse pilots and potentially cause them to take action they shouldn't, pilots said.

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