LE BOURGET, France -- French investigators' final report on the 2009 crash of an Air France jet that killed 228 people portrays a cockpit rapidly consumed by confusion and unable to decode a welter of alarms to determine which flight readings could be trusted, with the pilots' apparent reliance on a faulty display cementing the plane into its fatal stall.
The report, released Thursday by the Bureau of Investigation and Analysis, concluded that the errors were the outcome of a confluence of factors beyond the competence of any individual pilot. The investigators stood by earlier findings that the pilots had not been adequately trained to fly the aircraft manually in the event of equipment failure or a stall at high altitude.
There was a "profound loss of understanding" among all three pilots of Air France Flight 447, an Airbus A330 en route to Paris from Rio de Janeiro, about what was happening after ice crystals threw off the plane's airspeed sensors and the autopilot disconnected, the report said. The pilots then struggled to control the plane manually amid a barrage of alarms, a situation further confused by the faulty instructions displayed by an automated navigational aid called the flight director.
"The crew never understood they were in a stall situation," the report said, "and therefore never undertook any recovery maneuvers." It said further that "the combination of the ergonomics of the warning design, the conditions in which airline pilots are trained and exposed to stalls during their professional training and the process of recurrent training does not generate the expected behavior in any acceptable reliable way."
The report offered an answer to a central puzzle: the consistent and aggressive "nose up" inputs by the pilot at the controls, which added to the loss of lift. Pilots are normally trained to point the nose of the aircraft down in a stall to regain speed.
The report said that the readings being gathered by the automated flight director -- which uses cross hairs superimposed over an artificial horizon to indicate the required positioning of the plane -- would have resulted in repeated calls for the plane's nose to be lifted.
One aviation expert was troubled that the pilots did not appear to have the skills to start from the basic observation that airspeed indicators were giving conflicting readings and anticipate which of their flight readings -- like that of the flight director -- would therefore be untrustworthy.
William R. Voss, president of the Flight Safety Foundation in Alexandria, Va., said: "We are seeing a situation where we have pilots that can't understand what the airplane is doing unless a computer interprets it for them. This isn't a problem that is unique to Airbus or unique to Air France. It's a new training challenge that the whole industry has to face."
Investigators recommended that the European Aviation Safety Agency require Airbus to review the flight director's design and to possibly modify the software so that it either disengages permanently in the event of a stall or displays "appropriate orders" when a stall warning is set off.
Airbus, in a statement, did not address the questions raised about the cockpit navigation systems. Instead, it said it was working on various changes, including improving the design of the software.
Air France emphasized that its pilots had "acted in line with the information provided by the cockpit instruments and systems," adding that "the reading of the various data did not enable them to apply the appropriate action."
Investigators made 25 safety recommendations in their final report. Of those, eight were related to improvements in pilot training, while others focused on the programming of cockpit computers and stall alarm systems. The investigators also suggested ways to improve oversight of airlines and search-and-rescue operations.
The investigators' report does not seek to assign blame for the crash. But it could have legal implications.
The French news media reported late Wednesday that a judicial panel of experts advising a separate criminal inquiry into the crash had recommended that blame not be placed solely on the pilots, saying that Air France, Airbus and European safety regulators also shared responsibility.
The report, which was submitted late last week to an investigating judge, has not been made public. But according to a statement by the S.N.P.L., a French pilots union that has seen the report, the panel faulted Air France for shortcomings in its pilot training systems, as well as Airbus for weaknesses in the aircraft's design. Moreover, it said French and European air safety regulators should have acted more swiftly to order the replacement of the plane's airspeed sensors, which were known to be vulnerable to icing.
The sensors that failed on the doomed flight, known as Pitot tubes, were made by Thales, a French company. The European Aviation Safety Agency ultimately ordered the replacement of the Thales sensors on all Airbus A330 jets weeks after the crash of Flight 447 with a model made by Goodrich, an American company.
Airbus and Air France face accusations of involuntary manslaughter. It was not immediately clear if prosecutors planned to pursue criminal charges against either France's civil aviation authority or the European Aviation Safety Agency, which certified the airspeed sensors.
This article originally appeared in The New York Times.