With the recorders still missing, investigators are focusing on the automated messages sent by the plane minutes before it lost contact. One indicates the plane was receiving incorrect speed information from external monitoring instruments, which could destabilize the plane's control systems. Experts have suggested those external instruments might have iced over. Air France has now replaced the monitors, called Pitot tubes, on all its Airbus A330 and A340 aircraft.

But the mystery of what really caused the crash continues, leaving aviation safety experts unclear about what needs to be changed to stop a similar catastrophe in the future.

"Any time you have an accident that remains a question mark, it is a problem for the whole aviation community," Goelz said. "The aviation community and the public want to know what happened so we can prevent it from happening again."