What happened
On June 25, 1998, a Bolkow 105, registration EI-LIT, was conducting a private flight from Dublin Airport toward Falcarragh, Co. Donegal. The mission involved picking up passengers for a subsequent ferry flight to Tory Island. While flying approximately 2 nautical miles west of Slane, Co. Meath, the pilot experienced a sudden surge in noise and vibration levels within the aircraft.
In response to the instability, the pilot decreased engine power; however, the vibrations continued. Although the pilot confirmed the aircraft remained fully controllable and all primary systems appeared functional, the decision was made to perform a precautionary landing in a nearby field. The pilot emerged from the flight with no injuries.
The investigation
Following the landing, a technical examination of the aircraft was conducted. A post-flight inspection revealed significant impact damage to the stainless steel leading edge of one tail rotor blade. Additionally, investigators noted that the clamp and cover for the tail unit anti-conllision light were missing from the airframe.
Laboratory analysis of the damaged rotor blade involved examining the impact site using a Scanning Electron Microscope (SEM). Investigators discovered pink powder and red/orange glassy particles embedded in the composite material where the stainless steel cladding had been punctured. Chemical analysis confirmed these substances were composed primarily of silicon and zinc, identifying the debris as glass.
Findings
- The investigation established that the anti-collision light cover detached from the airframe during flight.
- The detached cover struck the tail rotor blade, causing physical damage to the leading edge.
- This impact created a mechanical imbalance, which resulted in the increased noise and vibration levels experienced by the pilot.