The Boeing-Vertol Model 234LR Chinook was normally based at Aberdeen Airport but had been operating from Sumburgh since 3 November to run a shuttle service to the Brent oilfield in the East Shetland Basin. On the morning of the crash, the first flight had been delayed by an oil leak from an engine gearbox, which was quickly repaired. The helicopter left Sumburgh at 08:58 with 40 passengers, visited three platforms in the Brent Field with exchanges of freight and workers, then departed Brent Platform C at 10:22 carrying 44 passengers for the return flight. As it approached Sumburgh and was cleared to descend, the crew reported their position at 4.5 miles from the airfield. The controller cleared them to land on helicopter runway 24. Nothing else was heard.

A catastrophic failure of a modified bevel ring gear in the forward transmission allowed the tandem rotors to lose synchronisation. When spinning rotor blades collide, the destruction is instantaneous and total. The helicopter was largely broken apart in mid-air, then struck the sea and sank rapidly. A Coastguard search-and-rescue Sea King helicopter, which had just departed Sumburgh on a training flight, spotted liferafts in the water, then a survivor clinging to wreckage. While winching that man aboard, the crew noticed a second survivor among the floating bodies. No others were found alive. Captain Vaid, a 45-year-old former Indian Air Force pilot who had flown Chinooks since 1982, was one of the two who survived. First Officer Neville Nixon, 43, who had returned to flying after helping his wife run a chemist's shop, did not.

The wreckage lay in roughly 90 metres of water with strong tidal currents and building seas. The diving support vessel Deepwater 1 began the search the following morning but struggled to hold position. Shell Expro's semi-submersible Stadive took over as primary recovery vessel and, within days, raised the cockpit voice recorder, the cockpit section, rotors, rotor heads, gearboxes, and control systems. These were sent to Aberdeen for analysis by the Air Accidents Investigation Branch. The Stadive recovered most of the fuselage and the bodies of the victims. In all, 44 of the 45 who died were brought home. The investigation concluded that the bevel ring gear had been inadequately tested after modification, and that inspection programmes had failed to catch the defect.

The AAIB made three principal recommendations: that certification procedures for modifications to vital components be strengthened, that condition monitoring systems for helicopters be improved, and that emergency beacon equipment be redesigned to survive high-impact crashes. The oil industry drew a broader conclusion -- the Chinook was too large for the offshore passenger role. The remaining Chinooks were withdrawn from North Sea service and eventually sold to Columbia Helicopters in the United States for heavy-lift cargo work. The disaster transformed helicopter safety standards in the North Sea, joining a grim sequence of offshore aviation accidents that collectively drove the most rigorous helicopter safety regime in the world. For the families of the forty-five who died, the legacy was more personal: a loss that reshaped communities across northeast Scotland and Shetland.