The report itself stops short of any final conclusions, which are not expected to be made public until early next year. But initial findings highlighted by investigators indicate that the two co-pilots in the cockpit at the time the plane ran into trouble had never been trained to fly the aircraft in manual mode, nor had they been instructed how to promptly recognize and respond to a malfunction of their speed sensors at high altitude — both crucial skills that experts say should have helped them to avert disaster.The report nevertheless fails to address the central mystery of the event: how, despite the persistent sounding of the stall warning alarm, none of the pilots thought "stall" or suggested that the pilot in command drop the nose:
As abruptly as the plane climbed — at 7,000 feet per minute, more than twice the rate at take-off — its recorded speed declined, dropping almost instantaneously from 275 knots to 60 knots, the minimum valid velocity recognized by the plane’s computers.
A stall warning sounded twice. The pilots tried several times to call the captain back from his rest area. However, the investigators noted, “neither of the pilots made any reference to the stall warning” — a departure from standard industry procedures. “Neither of the pilots formally identified the stall situation,” they added.
About a minute later, the captain returned to the cockpit. The plane’s airspeed readings continued to fluctuate wildly. Meanwhile, its nose was pointing upward from the airstream at about 16 degrees — far beyond the maximum angle of around 5 degrees that is considered to be safe at high altitudes, where the air is thin.
But the pilots could not know this, the report said, because that information — known as the angle of attack — is not directly displayed in the cockpit.
As the plane plunged toward the sea at vertical speed of nearly 11,000 feet per minute, its angle of attack continued to increase, at one point exceeding 40 degrees.
Investigators recommended Friday that air safety regulators worldwide consider requiring jet manufacturers to include an angle of attack indicator “directly accessible to pilots.”