What happened
On 10 April 2003, an Aerospatiale AS350B1 helicopter, registration G-BWFY, was performing aerial work near Bakewell, Derbyshire. The mission involved supporting the installation of a mobile phone mast by transporting external loads to a site located within a tree-filled bowl on a plateau.
After successfully delivering several loads of concrete, the pilot attempted to place the final triangular section of the mast into a small clearing. As the pilot hovered the load approximately three metres above the surrounding trees, the ground crew moved the load abruptly to the right. This sudden movement caused the helicopter to drift and descend. The pilot felt a vibration through the tail rotor pedals, and the ground crew subsequently released the load.
Believing the tail rotor had struck the trees, the pilot landed at a nearby refuelling site to inspect the aircraft. He identified that the tail rotor tracking lobes had been bent, indicating a blade strike, and noted visible marks on tree branches. After performing a self-assessment and straightening the lobes, the pilot deemed the aircraft serviceable and continued operations.
The investigation
Following the incident, the pilot reported the event to an engineer, who performed a detailed inspection of the tail rotor gearbox, drive train, and blades. While the aircraft was initially cleared for flight, a routine inspection three days later—after 13.4 hours of subsequent flight time—revealed significant structural issues. The investigation established that the blade skins had de-bonded from the foam cores on both sides of two blades, with one blade showing 50% de-bonding on the inboard side.
Findings
- The primary cause of the tail rotor strike was the unannounced and violent movement of the external load by the ground party.
- The pilot's initial assessment of the damage was insufficient to identify the internal structural de-bonding.
- The maintenance inspections following the incident were routine and did not include a specific monitoring protocol for that particular tail rotor.
Safety action
- The operator highlighted the necessity for flight crews to seek professional engineering support for both determining aircraft serviceability and performing any required repairs.