History of the Flight
On 26 September 2012 at 0825 UTC, a Sikorsky S-76C helicopter, registration G-CGOU, was flying from Humberside Airport to a platform in the Ravenspurn Gas Field. During a short cruise climb, the helicopter began to pitch nose up and roll to the right. The commander disengaged the autopilot and established straight and level flight. The co-pilot remarked that he could smell smoke and suggested returning to Humberside. As the commander turned the helicopter, he noticed an uncommanded “fishtailing” yawing motion. The crew transmitted a ‘PAN PAN’ call and informed ATC. Although no visible smoke was present, a strong smell persisted. The commander decided to make a precautionary landing at a private coastal airfield less than two miles away. The eight passengers were briefed, and the landing was completed safely.
Injuries and Damage
No injuries were reported among the two crew members or the eight passengers. The helicopter sustained no damage.
Investigation
After landing, circuit breakers for the number 2 cyclic control trim and the collective control trim were found tripped. An engineering investigation established that electrical shorting had occurred in a wiring loom situated above the forward left cabin area. The operating company issued a fleet-wide technical directive to inspect the wiring loom for signs of damage and to take corrective action where appropriate. A temporary repair was carried out in accordance with manufacturer’s procedures, and the aircraft was flown to a maintenance base for a permanent repair. Following tests and checks, the helicopter was returned to service.
Manufacturer Response
The manufacturer, in contact with the operator, considered that the wiring bundles were probably disturbed during a customer option installation. The manufacturer also recognized that the area is potentially susceptible to chafing and is currently studying methods of product improvement to reduce this susceptibility for both future and delivered aircraft.