Investigators have confirmed that the crew of a Eurocopter AS332 L2 helicopter transmitted a 'Mayday' call before the aircraft crashed into the North Sea yesterday with the apparent loss of all 16 on board.
UK Air Accidents Investigation Branch officials state that the distress call was "brief" and that the aircraft, identified as G-REDL, was "seen to descend rapidly" and strike the surface of the sea.
Recovery teams are preparing to locate and retrieve the aircraft's combined voice and flight-data recorder.
Fourteen passengers and two pilots were on board the aircraft, operated by Bond Offshore Helicopters, and eight occupants are confirmed dead. There is no evidence of any survivors.
Ten of those on board were employees of Aberdeen-based KCA Deutag Drilling. The company says that the aircraft was operating a crew-change service for the BP Miller platform, and the helicopter was returning to Aberdeen.
"The cause of the crash has not yet been verified but we know that weather conditions were good," it adds.
Representatives of the French accident investigation agency Bureau d'Enquetes et d'Analyses, Eurocopter and the European Aviation Safety Agency have been invited to participate in the inquiry.
Search efforts resumed at 06:30 today after being suspended overnight. Bond's offshore flight information centre indicates that all services today to the various oil fields have been cancelled, while the transport union RMT says the helicopter type should be grounded pending investigation.
"Reports indicate that the crash was the result of a catastrophic failure in the aircraft, and it would make sense for the model involved to be grounded until it is clear what caused it," says RMT offshore organiser Jake Molloy.
Two Royal Air Force rescue helicopters were scrambled after the Coast Guard received notification, just before 14:00 yesterday, that a helicopter had ditched about 22km off the coast of Crimond, between Fraserburgh and Peterhead.
Lifeboats were dispatched and a British Aerospace Nimrod maritime patrol jet diverted to assist, while several other vessels headed for the search area. Two overturned liferafts were seen in the water.
Yesterday's accident came just six weeks after a Eurocopter EC225 Super Puma, also operated by Bond, ditched near an oil platform on 18 February. All 18 occupants were rescued.