June 6, 2012— -- The Airbus A330 has one of the most sophisticated automated piloting systems in the airline industry, but the 2009 crash of Air France Flight 447 has some experts saying that the pilots weren't adequately trained to handle the plane in an emergency situation, and that the plane's stall alarm system may have added to the crew's confusion and contributed to the disaster.
The crash, which killed all 228 passengers and crew on board, is considered one of the worst -- and most mysterious -- aviation disasters in modern history. One theory for what caused that Airbus A330 to go down is that the two co-pilots, led by 58-year-old Captain Marc Dubois, were not properly trained and depended too heavily on the plane's autopilot system. That system disconnected at high-altitude when a speed sensor, called a pitot tube, froze over, sending inconsistent readings to the plane's computers.
Air France declined ABC News' request for an interview, pending the July release of the final report from France's investigation. But according to Bill Voss, the president and CEO of the Flight Safety Foundation, Air France was so confident in the design of the Airbus A330, the airline had not trained nor prepared its pilots for the situation the crew of Flight 447 encountered the night of the crash.
"No one was trained for high-altitude stall recovery in the cockpit," said Voss. "It's not part of the normal training curriculum...this is something that really has to be reformed globally. This is a really big deal."
PHOTOS: Air France Flight 447 Crash Wreckage Recovered
Air France Flight 447 was en route from Rio de Janiero to Paris on May 31, 2009, for an overnight trip, when it vanished. The plane crashed into the Atlantic Ocean in the early morning hours of June 1, 2009 -- nearly four hours after take-off.
Black box tapes were recovered from the wreckage two years later in April 2011 and, amazingly, still worked. The tapes revealed that almost four hours into the flight, the plane was 800 miles off the coast of Brazil, and Captain Dubois left the cockpit for a scheduled nap. At the time, the plane was about to fly into a thunderstorm, one that other flights that night had steered around.
Once in the storm, the plane's pitot tube, a critical piece of equipment that tells the pilot the aircraft's air speed, failed, likely from ice crystals forming on it, according to BEA officials who inspected the wreckage. When the pitot tube fails, the Airbus's automatic pilot system disengages, shifting control back to the pilot.
According to the tapes, First Officer Cedric Bonin, a 32-year-old pilot who had fewer than 5,000 flight hours under his belt, was at the controls but had never been in this situation before at high-altitude. Bonin made the fatal mistake of pulling the plane's nose up, which caused it to go into a deep stall.
"It seems that the pilots did not understand the situation and they were not aware that they had stalled," said Jean-Paul Troadec, the director of BEA, the French authority conducting the investigation into the Flight 447 crash.
When the Airbus A330 goes into a stall as severe as what happened to Flight 447, Voss said the plane's computer rejects the data it's receiving, thinking the plane couldn't possibly be flying in such a radical condition, and then shuts off the stall alarm.
"The computer is thinking 'this doesn't make any sense, we must be on the ground. We must be parked at the gate or we would be dead,'" Voss said.
Airbus claims the stall alarm on Flight 447 "was performing as designed," and said there is rationale behind its design.
"If you get as low as 60 knots, the stall warning will cut out by design, and we do that because on landings and take-offs at a low air speed, when the angle of attack is erratic and it may not be reliable, we cut that out so it would not distract pilots during take-offs and landings," said Bill Bozin, the vice president of safety and technical affairs at Airbus.
As co-pilot Cedric Bonin pulled continuously up on the controls, the stall alarm sounded for 54 seconds straight. But as Flight 447 went deeper into its catastrophic stall, the alarm cut in and out intermittently, the black box tapes revealed. The stall warning was working as designed, but critics charge the pilots would have been confused by the mixed signals.
The co-pilots called frantically for help from the captain, the black box tapes showed, but it took Dubois more than one minute to return to the cockpit.
"What's happening?" Dubois is heard asking when he re-enters the cockpit.
"I don't know what's happening," one co-pilot responded.
It was not until the final three seconds before the plane hit the Atlantic that the pilots even realized they were going to crash, the black box tapes revealed. Co-pilot David Robert is heard on the tape recording saying, "Oh my God, we're going to crash. I can't believe it." The last words on the recording are Bonin saying, "But what's happening?"
VIDEO: What It Was Like in the Flight 447 Cockpit
BEA did not originally release the pilots' final words. That part of the tape was later leaked.
Troadec said the agency withheld it from the public because the tape contained "personal conversations that is not useful to understand the accident."
But this decision led many people, including the victims' families, to suspect that the BEA was not telling the whole story. The agency will release its final report on the investigation of the crash on July 5, 2012.
INFOGRAPHIC: Air France Flight 447: Timeline of Events
About 180 victims' family members have sued Air France and Airbus over the crash. The family of one of the victims, Eithna Walls, has settled its lawsuit. But Airbus continues to defend its planes and their design.
"The 330 has accumulated seven million flights and over 37 million flight hours," said Bozin at Airbus. "Its operational performance, its reliability, its safety, have been well established."
"Airbus is proud of the fact, they like to say that their plane is 'pilot-proof,'" said aviation lawyer James Healy Pratt. "It's designed so that it overrides any pilot error so that the computer will be in charge."
The A330, considered among the safest in the skies, has flown over 800 million passengers across the world and there are 865 planes in operation today, according to Airbus's website. But in modern aviation, these planes almost fly themselves. Voss said that on any given flight, pilots are manually flying the plane for only three minutes -- one minute and 30 seconds each for take-off and landing.
"We moving towards automated operations where the pilot isn't even permitted to fly," Voss said. "That means the first time in your career you will ever feel what an aircraft feels like at 35,000 feet is when it's handed to you broken [if something goes wrong and the automated system disengages]."
At the heart of the heated debate over so-called "automation addiction," which is when pilots are overly dependent on computers to fly their planes, is the question of whether pilots are actually learning how to properly fly large commercial aircraft.
"Because of this sophistication and the ability of airplane to fly themselves, they don't have as many people to actually fly the airplane, to actually exercise their stick and rudder capabilities," Bozin said.
ABC News' Lauren Effron contributed to this report