History of the Flight
The helicopter, a McDonnell Douglas Hughes 369E registered G-SIVA, was flown from Manchester to a private landing site in eastern Kent by another pilot. During his pre-flight check at Manchester, that pilot did not observe any damage on the tail rotor. After arrival at the owner's site, the owner boarded the helicopter and flew it to Shoreham Airfield, the base from which it was occasionally operated. Neither pilot could subsequently recall whether the owner had boarded with the rotors running or if the engine had been shut down and restarted, leaving uncertainty as to whether a pre-flight inspection had been performed at the owner's site. The flight to Shoreham was uneventful and lasted approximately 20 minutes. After landing, the helicopter was shut down and left parked outside the operator's hangar.
Later, the owner planned to fly home and conducted a pre-flight inspection. During this inspection, he noted what appeared to be an 'open cut' in the leading edge of one tail rotor blade. The helicopter was declared unserviceable, and the AAIB was informed.
Examination of the Damaged Tail Rotor Blade
Subsequent examination revealed that the shape and edge characteristics of the cut were consistent with an impact by a thin, square-faced metallic object presented 'edge-on' to the rotor blade while the rotor was running. The impact had sheared out and coiled a narrow strip of the blade's leading edge material, indicating a high-energy impact. Sharp corners were present on both sides of each end of the cut. Forked fatigue fractures had propagated from two of the corners (one on each face of the blade), with the longest extending approximately 1 cm. The object that caused the cut could not be identified from the impact damage, but the degree of damage suggested it was fairly small. The extent of the fatigue cracks indicated it was unlikely they had developed during the flight from Manchester.
The owner had recently constructed a new hangar and landing pad at his home site. Aware of potential hazards, he had taken measures to ensure all debris was cleared before using the site. After the discovery of the damage, a further search of the site did not uncover any debris of the type that appeared to have inflicted the damage.
Findings
The cut on the tail rotor blade was not observed before the flight from Manchester but was discovered during a pre-flight inspection at Shoreham. Fatigue cracks had begun at the corners of the cut, but their extent suggested they did not develop during the earlier flight. The source of the impact remained unidentified.