The helicopter left the Safe Feliciasemi-submersibleoil rig in the Forties oilfield at 13:45 with 2 pilots and a full load of 19 passengers for the one hour flight to Sumburgh Airport on the Mainland of Shetland. At 14:28 the co-pilot reported hearing a muffled bang which was also heard by some of the passengers, from the area of the No. 2 engine transmission. Shortly after, the No. 2 engine's fire warning lights came on. The pilot immediately began a descent and transmitted a distress call. About 48 seconds after the noise, the No. 2 engine was shut down and the fire extinguisher triggered. The No. 1 engine fire warning then also illuminated, while passengers saw oil leaking from the cabin ceiling. The pilot advised the passengers to prepare for an emergency ditching and took control of the aircraft. The floats were deployed and a gentle ditching was made about 3 minutes after the initial noise had been heard, by which time the helicopter's cabin had filled with smoke. All 21 occupants evacuated on to liferafts and were then winched up into a Search and Rescue helicopter. After a strong fire consumed most of the floating helicopter, the remains broke up and sank.
Investigation
A recovery operation was mounted using the DSV Stena Marianos which arrived on site on 16 July 1988. The aft fuselage section was raised the following day and the forward section shortly after. The recovery operation had to be ended on 19 July before finding the engines or transmission components due to the Stena Marianos having other commitments. The recovery continued on 2 August using the DSV Norskald, and the engines, main rotor, and transmission were located and raised on 5 August.
Cause
It was concluded that the fire had occurred in the helicopter's main gearbox, probably resulting from the effects of a bearing failure in the No. 2 engine. A further factor was the lack of fire detection or suppression capability within the gearbox bay. The cause of the bearing failure could not be definitely established.
Safety recommendations
The AAIB made a list of 27 safety recommendations to the CAA. These addressed improvements in maintenance, early detection of problems, emergency escape equipment, documention and training provisions, and firewall integrity. Most of these were accepted by the CAA.
