(Reuters) - As investigators hunt for what caused an AirAsia jet to crash in an equatorial storm on Dec 28, the aviation industry is still struggling to apply the lessons of accidents in similar weather over the past decade.
It is too early to say whether the Airbus A320 crashed into the Java Sea due to pilot error, mechanical problems, freak weather or - as most often happens in aviation disasters - a combination of factors.
But its apparently uncontrolled plunge, coming after a series of other fatal crashes blamed at least in part on loss of control, has refocused attention on whether pilot training programs need to improve.
Critics say pilots don't get enough training on how to react when an airliner stalls or loses lift, and that changes in guidance about best practices have been slow.
"The lessons have not been learned to this day," said David Learmount, one of the aviation industry's leading safety commentators. "Everyone knows what the problem is, but nobody is doing anything about it."
Though rare, loss of pilot control ranks as the single biggest cause of air travel deaths. Two crashes in particular forced the issue - the 2009 losses of an Air France flight from Rio De Janeiro to Paris, and a Colgan Air turboprop near Buffalo, New York.
In both, confused pilots ignored or countermanded warnings of an impending stall, a condition where a plane loses lift because the air flow over its wings is too slow.
The Air France jet took a four-minute, 38,000 feet plunge into the ocean. Despite repeated stall alarms, the control stick was fatally yanked backwards. (reut.rs/nHRIZX)
Classic stall training calls for pilots to push the control stick forward, nosing the plane down so it will swoop lower and regain speed, which is effective but uncomfortable.
But over the last 30 years, most airlines encouraged their pilots to hold the control stick broadly steady and gun the engines to power their way out of a stall, trying to keep the ride as level as possible.
In examining stall crashes from that period, that procedure "wouldn't have helped and would have led to more accidents than it prevented," said Claude Lelaie, a retired former chief test pilot at Airbus.
In a rare joint move from 2009, Airbus and Boeing called for a return to robust cockpit procedures that prevailed "when the old guys like me were being trained," Lelaie said. "We were told to push the stick at the first sign of a stall."
But it took several years to set rules that ensure pilots receive regular refresher training and to root out the disputed cockpit procedures of past decades.
The new voluntary guidelines by the United Nations International Civil Aviation Organization (ICAO), which coordinates safety, took effect just six weeks before the loss of AirAsia Flight QZ8501, and will take years to be implemented around the globe.
New U.S. rules on pilot training do not take effect until 2019. Regulators will require flight simulators to better model stall behavior, changes that will also take years to implement.
ICAO also has proposed that pilots refresh their stall training by flying small aerobatic planes. But Learmount and others said most airlines would be reluctant to pay for it.
Changes in training cannot be made overnight because they can create other risks. Even minor adjustments must be thoroughly researched to avoid sowing the seeds of future accidents.
The industry is wrestling with a steep drop in the time pilots spend manually flying. Pilots now typically steer for only a few minutes at takeoff and landing, and rely on autopilot for the lengthy, boring cruise phase of flight.
When a sudden upset occurs - such as icing or powerful air currents from a storm - even the best pilots can experience a "startle effect" and may struggle to recall manual flying skills for that rare situation.
A study by Australia's Griffith University found a person's ability to process information is significantly impaired for 30 seconds after being startled, so being trained to cope with the unexpected is as important as knowing cockpit theory.
Flight simulators pose another challenge. The machines are crucial because pilots get little or no in-flight training for stalls after basic training.
But most simulators still cannot accurately model a plane's behavior in a full stall. The Federal Aviation Administration has pressing to make them better in a rule-making process that closed this week.
Simulator makers want better data about stalls to improve their machines. But plane makers say airliner stalls are so unpredictable that the data would be of little value - a dispute that could also have implications for any potential liabilities.
"It's not clear how the simulation data will be collected," said Pat Anderson, director of flight research at Embry-Riddle Aeronautic University, the largest U.S. flight training school.
Around the world, airlines, flight schools and governments vary widely in how swiftly and fully they adopt the changes.
Some airlines train in-house and go beyond what's required. Others just meet minimum standards, said David Greenberg, a consultant and former head of flight operations at Delta Air Lines.
"Training is still a patchwork quilt," he said.
Reporting by Alwyn Scott in New York and Tim Hepher in Paris; Editing by Martin Howell