June 2, 2009 / 11:11 PM / 11 years ago

FACTBOX: How planes get lost

REUTERS - Aviation experts were at a loss to explain how an Air France jet with 228 people on board could have crashed into the Atlantic Ocean earlier this week, and there were no distress messages or signals received from emergency beacons that should have transmitted automatically.

Planes know where they are but don’t necessarily share the information when they are in remote locations out of air traffic control range, due to technological and regulatory issues, safety experts say.

Following are details of how planes are kept track of — and lost.

- Planes can determine where they are anywhere in the world using Global Positioning System (GPS) satellite technology, just like cell phones and car systems. Because position is determined using signals constantly sent from satellites, it can be done globally. But airlines are not required constantly to send that data to air traffic control authorities.

- Oceanic flights can use satellite-based communication systems to transmit their location to their companies. This might typically occur for maintenance purposes, and with information sent automatically by the aircraft or the crew. The Air France flight sent information about its electrical failure shortly before disappearing.

- National air traffic control systems use radar and radio signals to keep track of flights in their air space; ground-based radar establishes where planes are, and planes regularly radio their identity.

- Flights over oceans and in some other remote areas can go ‘off the grid’: they fly beyond the reach of radio signals and radar because of the curvature of the Earth.

- The United States is building a GPS-based air traffic control system, and plans are for full rollout by 2013, depending on levels of government funding. Parts of the system are being put in place now.

* Based on information from flight tracking company Blue Sky Network, the Flight Safety Foundation, and the U.S. Federal Aviation Administration (FAA).

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