What causes a passenger jet to suddenly plunge intact–with engines and wing surfaces working just fine–from cruising altitude into the middle of the Atlantic Ocean, killing everyone aboard?

The full report on Air France Flight 447 in 2009, in which 228 people died, is still in the works. But one expert told me that preliminary data suggest a role for human confusion, and a failure to focus on the plane’s “attitude” or position in the sky: nose up or down, wings tilting left or right.

“You have a perfectly good airplane, other than not having airspeed data,” R. John Hansman, aeronautics professor at MIT, mentioned to me today after we discussed the release of preliminary data on the accident, recovered from “black boxes” fetched from 12,000 feet below the surface of the ocean. “They clearly lost situational awareness. If they’d had it, they would have been able to regain control of the airplane.”

French investigators have said that the plane was entering an area of turbulence, possibly severe. They’ve also said the plane suffered a failure of its airspeed indicators, possibly because of icing on a sensors known as a pitot tubes.The aircraft climbed from 37,500 feet to 38,000 feet, and “stall warning” was triggered.

This meant they were in danger of losing “lift.” Why those warnings were sounding—whether they were valid, or based on inaccurate speed data–or whether the pilots ignored the stall warning because they saw high speeds that were inaccurate, is unclear.

Either way, the loss of the speed data and the approaching turbulence were far from conditions that would automatically produce a catastrophe. “The normal training for that type of event,” Hansman said, “is to believe your attitude indicators, and ignore your airspeed indicators.”

Multiple sensors provide “attitude” information. There was no indication any of them on the Airbus A330 jet were malfunctioning. So, whatever else was happening, the pilots should have kept their eyes on those–and focused on keeping the plane level. If they kept engine thrust at normal levels and kept their eyes on attitude indicators, they should have pulled through.

“Nose slightly above horizon. Wings level. They should have kept bringing that airplane back to that indication. It was obviously showing something different than that,” Hansman says. But focusing on attitude alone, he added, “can be very difficult because airspeed indicators are very compelling and you are getting warnings.”

It was late at night, more than four hours into the flight. Stall warnings were sounding. Speed indicators were going haywire. The captain had been called to the cockpit by an alarmed co-pilot. It took only about three minutes for the plane to plunge 38,000 feet to crash, belly first, on the surface of the ocean.