How Accidents Are Investigated
Accidents rarely result from a single failure or action. They result from a combination of things -- for example, an error in maintenance that causes a failure in flight that a member of the flight crew then responds to incorrectly. In other words, accidents result from a chain of events that make them difficult to analyze but also provide multiple opportunities to prevent them. Remove any link in the chain and the accident is avoided.
Industry and government safety experts study accidents to identify these chains of events as well as "intervention strategies" for preventing the same kinds of accidents in the future. The strategies include new training aids for flight crews and mechanics, new operating procedures, infrastructure improvements, aircraft design modifications, and incorporation of new technologies into the aviation system. Working together, industry and government safety officials have been able to virtually eliminate some of the most common accident causes of the past and are confident they'll be able to do the same with the most common accidents still occurring.