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.
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.
The Sikorsky S-61N helicopter Oscar November (registered G-BEON) was owned by British Airways Helicopters, configured to seat 24 passengers, and typically operated between Aberdeen and the oil platforms of the North Sea. On 24 June 1983, Oscar November was assigned to act as a replacement for the British Airways Helicopters commercial passenger service between Penzance and the Isles of Scilly. The helicopter that usually operated the service, a Sikorsky S-61NM fitted with 32 passenger seats, was out of action while it was being repaired. On 3 July 1983, Oscar November received its annual certificate of airworthiness. Manufactured in 1977, Oscar November's airframe had flown a total of 7,904 hours, 49 of which had been since the last certificate of airworthiness.
The crew consisted of pilots Captain Dominic Lawlor (37 years old) and Captain Neil Charleton (30), along with cabin attendant Robin Lander (22). Lawlor was designated as the commander for the flight, while Charleton acted as co-pilot. Lawlor had flown a total of 3,970 pilot hours prior to the flight, of which 2,820 had been in an S-61N helicopter, and although he was based in Aberdeen, he had flown the Penzance–St Mary's route over 50 times before. Charleton was based in Beccles, but had also flown the route before, over 100 times. He had a total of 3,737 pilot hours, of which 2,280 had been in an S-61N. The 20-minute Penzance–St Mary's route was flown regularly during the summer; with 12 scheduled return flights running six days a week.
Oscar November was one of two flights scheduled to fly from Penzance Heliport to St Mary's Airport on the Isles of Scilly on the morning of 16 July; the other was G-BDDA (Delta Alpha), another S-61 helicopter. Delta Alpha had been scheduled to depart at 7:50 am (GMT), while Oscar November was due to leave at 8:15 am, but both flights were delayed by poor visibility. The weather forecast from the Plymouth Meteorological Office that morning warned of fog from 7:00 am until 5:00 pm, with visibility typically between 1–4 kilometres (0.62–2.49 mi), but as low as 100 metres (330 ft) in fog banks. The actual visibility recorded at St Mary's Aerodrome increased from 1.2 kilometres (0.75 mi) at 9:30 am to 2.2 kilometres (1.4 mi) by 11:30 am. Delta Alpha departed at 10:46 am, and landed at St Mary's at 11:06 am. With the possibility of the weather worsening, Lawlor waited for confirmation that Delta Alpha had landed and flown the entire journey according to visual flight rules (VFR). The minimum requirements to conduct a VFR flight were 900 metres (3,000 ft) of visibility, with a cloud ceiling of 200 feet (61 m). Having received confirmation, Oscar November departed Penzance at roughly 11:10 am, with 23 passengers on board, on flight BA 5918.
Oscar November climbed to a height of 2,000 feet (610 m), and as they passed by Longships Lighthouse, about 1.25 miles (2.0 km) off the coast of Land's End, the visibility was recorded as being between 0.5 and 0.75 nautical miles (0.93 and 1.39 km; 0.58 and 0.86 mi). During the investigation into the crash, Lawlor and Charleton reported that they received a verbal weather report from the crew of Delta Alpha, who were passing on their return flight. According to the pair, they were told that visibility was 0.5 to 0.75 nautical miles (0.93 to 1.39 km; 0.58 to 0.86 mi) at 300 feet (91 m). However, the crew of Delta Alpha did not recall talking to the Oscar November crew at any time during their flight. Based on this information, which he interpreted to mean that the cloud base was at 300 feet, Lawlor descended to 500 feet (150 m), to be able to analyse the situation better on their approach. For his part, Charleton had interpreted the message differently, believing that 300 feet had referred to the height at which Delta Alpha had been when they made the observations, but the pair did not discuss the report.
At 11:30 am, Charleton communicated with St Mary's, indicating that they were level at 500 feet, and were halfway through their crossing. They maintained good visibility with the sea below them, and although haze limited their forward visibility so that they could not see the horizon, they were confident it was in excess of the VFR minimum of 900 metres. Roughly 6 nautical miles (11 km; 6.9 mi) from St Mary's, Lawlor began to descend to 250 feet (76 m), the minimum height permitted, as he expected the cloud base to be at 300 feet. Both pilots confirmed with their instruments when that height had been attained, and thereafter Charleton concentrated on his radar and communicating with St Mary's. Lawlor then reduced speed, during which the vertical gyro indicator gave a brief warning of an attitude failure; however Lawlor checked the instruments, which appeared normal. Confident that the weather had improved, Lawlor stopped monitoring his instruments, and flew by visual aids only.
At roughly 11:35 am, following a string of communication between Charleton and St Mary's, the last message was sent from the aerodrome; "Oscar November is clear to land 300 degrees at 5 knots." When Oscar November was roughly 1.5 nautical miles (2.8 km; 1.7 mi) from the coast, the helicopter crashed, hitting the sea three successive times. Both Lawlor and Charleton thought that the aircraft was still at 250 feet, though one of the passengers, Lucille Langley-Williams, said that the cabin attendant had told her they were flying at around 100 feet (30 m) shortly before the crash.
The Sikorsky S-61 was fitted with floats on either side, known as "sponsons", and the base was designed to be like the hull of a boat, so that the helicopter could float. However, the heavy impact broke both sponsons off and broke the floor, letting water into the helicopter. Lacking the stability that the sponsons would provide, the fuselage rolled over, letting water in even quicker, and sank.
Only 6 of the 26 people on board escaped from the helicopter; Lawlor exited through the emergency exit window by his seat, while Charleton and a child got out through the forward freight bay. Another child managed to escape via the rear freight bay, and two adults exited through the starboard airstairs door. In addition to the two pilots, the survivors were Howard Goddard (age 12), Ellen Hanslow (15), Lucille Langley-Williams and Megan Smith (both 60). Ellen spotted Goddard struggling in the water, and she swam to help him. None of the six had managed to retrieve a life jacket, and so the two pilots gathered the survivors together, and helped keep them afloat, using suitcases as flotation aids. The incident was the worst civilian helicopter crash in the United Kingdom since 1981, when eleven oil workers and both pilots died in the 1981 Bristow Helicopters Westland Wessex crash.