During a flight from Hawarden Airport, the pilot noticed a stone obelisk when approaching Rhobell Mountain and decided to take a closer look. Having flown past at 20m, he brought the helicopter into a hover. However, the helicopter suffered a loss of thrust from the tail rotor while hovering close to the ground near a mountain top, resulting in a loss of control and a hard landing. The pilot vacated the cockpit and suffered minor injuries.
The investigation found that the tail rotor gearbox revealed damage to the bevel gears and failure of a bearing, which was consistent with inadequate cooling and a lack of lubrication. In addition, there were inconsistencies in the way maintenance was performed on the tail rotor gearbox, compared to the helicopter manufacturer's maintenance instructions. It is likely that insufficient oil was added to the tail rotor gearbox when it was serviced 25 flying hours prior to the accident.
As a result of the AAIB's findings, three Safety Recommendations have been made relating to information in the helicopter Maintenance Manual regarding the required oil quantity and maintenance servicing interval for the tail rotor gearbox.
