New black box tracker can find crashed plane in 1km-deep waters

♦a new black box tracker can find downed planes at the bottom of British waters, the Air Accident Investigation Branch has announced.

The Towfish Underwater Locator Beacon detection system can operate down to 1km below sea level, meaning for the first time it will be possible to find a crashed aircraft at the bottom of all UK coastal waters.

The Towfish device is dragged behind a surface vessel and “flies” just below the waves. It listens for the telltale “pings” of the black box, which get more frequent the closer it gets.

Commercial airliners have carried the beacons since the Seventies. On contact with water, the beacons “ping” a short pulse at frequencies of 37.5 khz and 8.8 khz every second for at least 90 days. The 37.5 khz frequency is limited in range and is hard to detect in very deep water as each “ping” only lasts for 10 milliseconds.

Adrian Burrows, of the Air Accidents Investigation Branch, told The Telegraph that although the two Towfish cost £400,000, “we are an island nation with a North Sea industry”, and it made sense to have a high-quality system. Most other countries used hand-held devices with inferior capability, he added.