What happened
On 19 November 1997, a Sikorsky S61N helicopter, registration G-BCLC, was engaged in a search and rescue mission near Bressay in the Shetland Islands. The mission was initiated after the MV Green Lily suffered engine failure and began drifting. Due to heavy seas and high winds, the vessel eventually ran aground, creating extremely hazardous conditions for the rescue operation.
As the helicopter attempted to winch survivors from the vessel, the situation became critical. During the final stages of the rescue, the winch operator noticed the Hi-line had become snagged on the ship's superstructure. To prevent the helicopter from being endangered, the operator activated the cable shear system to sever the line. However, the mechanism failed to cut the cable. During this period of instability, the winchman was swept overboard by a large wave and lost in the sea. The remaining survivors were successfully evacuated, but the winchman could not be recovered due to the extreme sea state and the subsequent failure of the winch equipment.
The investigation
The investigation focused on the failure of the Lucas Air Equipment Hoist's cable-cutting device and the circumstances surrounding the loss of the winchman. Examination of the cutting mechanism revealed that while the firing squib had functioned, the chisel had not severed the cable. Instead, the internal shearing pin had been incorrectly installed through the gas exhaust holes rather than the correct alignment holes, causing the blade to be positioned parallel to the cable.
Investigators also examined the Hi-line transfer method. It was found that the line had wrapped around the winch hook, which effectively bypassed the 150 lb weak link designed to protect the aircraft. Furthermore, the investigation noted that effective radio communication between the winch operator and the winchman on the deck was impossible under the prevailing environmental conditions.
Findings
- The 1 fatal injury occurred when the winchman was washed overboard and struck against the ship's side.
- The cable cutting mechanism failed because the guillotine blade was incorrectly oriented during maintenance.
- Maintenance manuals and worksheets lacked specific instructions regarding the correct orientation of the blade and the proper holes for pin insertion.
- The Hi-line became entangled around the hook, rendering the safety weak link ineffective.
- Severe weather and heavy seas prevented effective communication between the winchman and the helicopter crew.