Off the radar screen

Days after Air France’s ill-fated Airbus A330 plunged mysteriously into the southern Atlantic Ocean four hours after leaving Rio de Janeiro for Paris on May 31st, rescuers were still searching for debris.

The wreckage is thought to lie up to some 3,700 metres below the waves, possibly in one of the many trenches that riddle the rocky undersea mountain range west of the Mid-Atlantic Ridge. Its exact location may not be known for several weeks.

One of the hazards of flying over oceans is the lack of radar coverage. Even the latest radar equipment can reach out no more than 550 kilometres (300 nautical miles) from land. Once out of radar range, pilots flying intercontinental routes make scheduled radio contact every half an hour or so with air-traffic control stations, behind or ahead of them, to report their positions. The rest of the time, no one knows exactly where they are.

A number of countries, especially those surrounded by oceans or by vast expanses of rugged wilderness are none too happy with this. America, Australia and Canada have been among the most active proponents of satellite navigation for commercial aircraft.

The Canadian authorities began operation of such a system in January. It uses what is known in aviation circles as ADS-B, short for automatic dependent surveillance-broadcast. The technology combines the precise position of the aircraft, as identified by global-positioning satellites, with data about its flight number, speed, direction and attitude (whether it is climbing, descending or turning).

Although ADS-B would not have prevented the crash into the Atlantic Ocean, it might well have helped locate the debris more quickly. Knowing the exact location of the accident would allow rescue craft to be on the scene within hours, pulling any survivors from the water. That too would be a great benefit of the new air-traffic-control technology.

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