On 16 July 1983 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 helicopter civil aviation accident at the time.

An investigation was promptly carried out by the Accidents Investigation Branch (AIB), though calls for a public inquiry were dismissed. The AIB found that the accident was caused by pilot error, in failing to notice and correct an unintentional descent when attempting to fly at low altitude in poor visibility. Other contributory factors were found to be a failure to monitor flight instruments adequately, and a lack of audio height warning equipment.

The crash sparked a review of helicopter safety, and eight recommendations were made by the AIB. Of these, seven were adopted, most notably that it was mandatory for there to be audible height warnings on passenger helicopters operating off-shore. It remained the worst British civilian helicopter accident until 1986, when the Boeing 234LR Chinook helicopter G-BWFC crashed in the North Sea, with 45 fatalities.