What happened
On 18 October 2005, a Rotorway Exec 162F helicopter, registration ZU-DWD, was preparing for departure from runway 36L at Lanseria Aerodrome. During the initial stages of the takeoff roll, the pilot heard a loud noise originating from the rear of the aircraft. Recognizing the potential danger, the pilot immediately elected to abort the takeoff. The aircraft remained on the airfield, and there were no injuries resulting from the incident.
The investigation
Following the event, a technical inspection of the engine was conducted by a representative from Rotorway International SA. The investigation focused on the mechanical components of the engine's drive system. The inspection revealed that the drive belt retainer ring had detached from two of its four mounting bolts. This failure led to a secondary failure where the cooling fan blades broke and subsequently struck the tail drive pulley.
Findings
Technical analysis of the failed hardware showed a fine crystalline structure on the fracture surface, which is a clear indicator of metal fatigue. The investigation also noted that the aircraft was utilizing an after-market belt drive system, which had been installed to replace the original factory chain drive to achieve a 22 lbs weight reduction.
Safety action
While the manufacturer, Rotorway International, does not officially endorse after-market upgrades and had not issued a formal airworthiness directive for this specific component, they notified all owners of the findings. The manufacturer subsequently provided an upgraded retainer ring featuring a thicker design and a smaller inner diameter to prevent similar fatigue-related failures. The belt drive manufacturer also updated their design to incorporate a more robust retainer ring.