A Sikorsky S-61 helicopter operated by British Airways crashed in thick fog in the Celtic Sea, killing 20 of the 26 people on board.

The Sikorsky S-61L and S-61N are civil variants of the SH-3 Sea King military helicopter. They were developed and produced by the American helicopter manufacturer Sikorsky Aircraft.

British Airways plc (BA) is the flag carrier of the United Kingdom. It is headquartered in London, England at Waterside, near its main hub at Heathrow Airport.

On 16 July 1983, British Airways Helicopters Flight 5918, a British Airways Helicopters commercial Sikorsky S-61 helicopter, Oscar November (G-BEON), crashed in the southern Celtic Sea, in the Atlantic Ocean, while en route from Penzance to St Mary's, Isles of Scilly in poor visibility. Only six of the twenty-six people on board survived. It was Britain's worst civil aviation helicopter accident at the time.

The Celtic Sea is the area of the Atlantic Ocean off the southern coast of Ireland bounded to the north by Saint George's Channel; other limits include the Bristol Channel, the English Channel, and the Bay of Biscay, as well as adjacent portions of Wales, Cornwall, parts of Devon and Brittany. The continental shelf, which drops away sharply, delimits the southern and western boundaries. The Iroise Sea off Brittany is entirely included within it. The Isles of Scilly are an archipelago of small islands in the sea.