What Causes Commercial Jets To Crash

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 aides 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.
 

What happens when an airplane goes down

• The airport operator will handle fire fighting and rescue operations if the accident is at or near the airport.
• If not near an airport, local police and fire fighters quickly take control of the site to facilitate search and rescue and to protect important evidence.
  
• News media coverage is instantaneous and the demand for information far exceeds the supply.
• The National Transportation Safety Board (U.S.), or the government with jurisdiction over the area, is immediately notified.
• The affected airline is the responsible source of information about the passengers and crew on board. It will not identify victims prior to notifying next of kin. The airline typically will conduct media briefings from both the accident site and its headquarters.
• The airplane manufacturer and engine manufacturer will be involved in the accident investigation, if called upon by the airline or regulatory agency leading the investigation.

When an accident occurs, the NTSB (or its foreign equivalent) dispatches a "go team" to the site. The NTSB team usually consists of one of the five members of the board plus staff specialists in air traffic control, aircraft maintenance, aircraft operations, aircraft systems and other disciplines useful to determining an accident's cause. Representatives of the various parties to the investigation - usually the aircraft and engine manufacturers, the pilot and controller unions, and the government regulatory agency with jurisdiction over the accident site - also participate in the investigation. All outside parties, however, participate at the invitation of the government authorities leading the investigation, who retain full control over the investigation, oversee all testing and analysis of wreckage, and are solely responsible for determining probable cause.

Investigative process
While the initial field phase of an accident investigation can be concluded within weeks or even days, the investigators' final report and recommendations often take years to complete. Sometimes the investigative agency holds a public hearing, with witnesses, to gather additional information and opinions about what the evidence shows. NTSB investigations conclude with a "sunshine meeting" in Washington, D.C., at which the board votes on the official findings of fact and probable cause. Its final report also includes recommendations to the parties, the vast majority of which are implemented, often before the investigation is complete.

Always important to an investigation are the "black boxes" - the cockpit voice recorder and flight data recorder, which are encased in steel boxes located in the tail of every plane and capable of withstanding great pressure and temperature extremes. Radar tapes also can be valuable sources of information to accident investigators.

Black boxes
Following a jetliner accident, the media is quick to report on the search for the "black boxes," or the airplane's flight data recorder and cockpit voice recorder. Together, these two units tell the story of the flight. Actually painted bright orange, these recorders are equipped with "pingers" or radio and acoustic beacons that aid in their retrieval. These two recorders are critical for providing clues as to why an airplane went down. They enhance overall flight safety by helping airlines, manufacturers and regulators prevent similar losses in the future.

• Flight data recorder: A flight data recorder captures a flight's history. It records "air data" such as the airplane's speed, heading, altitude, rate of climb or descent, accelerations, and decelerations. The plane's systems and functions are also recorded, along with information about engine thrust and the position of control surfaces (flaps and rudder). Flight crew and autopilot control actions are also recorded. Older flight data recorders stored information on metallic foil and recorded relatively few things. Newer units record hundreds of "parameters" and store this information on microchips.
  
  
• Cockpit voice recorder: A cockpit voice recorder picks up all cockpit noises, radio communications, flight crew announcements, and flight crew conversations.

In their quest for answers, investigators study both the flight data recorder and the cockpit voice recorder to piece together the details of the accident. The cockpit video camera may soon be used to add a visual component to these diagnostic recordings.