PARIS – Confronted with faulty instrument readings and alarms going off in the cockpit, the pilots of an Air France jetliner struggled to tame the aircraft as it went into an aerodynamic stall, rolled, and finally plunged 38,000 feet into the Atlantic Ocean in just 3 minutes.

But the passengers on that doomed Rio de Janeiro-to-Paris flight were probably asleep or nodding off and didn’t realize what was going on as the aircraft fell nose-up toward the sea, the director of the French accident investigating bureau said after releasing preliminary black-box data on the June 1, 2009, disaster. All 228 people aboard the Airbus A330 died.

The report by the BEA offers no analysis and assigns no blame. It also does not answer the key question: What caused the crash?

But several experts familiar with the report said the co-pilot at the controls, at 32 the youngest of the three-man cockpit crew, Cedric Bonin, may have responded incorrectly to the emergency by pointing the nose upward, perhaps because he was confused by the incorrect readings.

The plane’s external speed sensors, called Pitot tubes, have long been considered a likely culprit in the disaster, with experts suggesting they may have been iced over. BEA investigators found that two sets of instruments on the plane gave different speed readings. Since the accident, Air France has replaced the speed monitors on all its Airbus A330 and A340 aircraft.

An official at Airbus said the aircraft’s nose should have been pointed slightly downward to enable the plane to regain lift after it had gone into an aerodynamic stall.

The flight data recorder and cockpit recorder showed, in addition to inconsistent speed readings, two co-pilots working methodically to right the plane manually after autopilot stopped. Captain Marc Dubois returned from a routine rest to the cockpit amid what moments later became a catastrophic situation.

After the plane went into a stall, warnings sounded, the autopilot and autothrust shut off as designed, and the co-pilot not at the controls “tried several times to call the captain back,” the BEA report said. The captain returned one minute and 10 seconds later, when the plane had climbed to 38,000 feet.

“During the following seconds, all of the recorded speeds became invalid and the stall warning stopped,” the report said, but added that the plane never came out of its aerodynamic stall.

“The airplane was subject to roll oscillations that sometimes reached 40 degrees,” the report said.

The passengers probably fell to their deaths without knowing they were doomed, BEA director Jean-Paul Troadec said on RTL radio.