What happened
On 21 August 1999, a McDonnell Douglas Hughes 369E, registration G-SIVA, was involved in an incident at Shoreham Airfield. The helicopter had previously been flown from Manchester to a private landing site in eastern Kent by a different pilot. Upon arrival at the Kent site, the owner took command of the aircraft and flew it to Shoreham for a 20-minute private flight. After landing and parking the aircraft outside a hangar, the pilot conducted a pre-flight inspection for a subsequent intended flight. During this check, the pilot identified an 'open cut' on the leading edge of one of the tail rotor blades. The aircraft was immediately grounded and declared unserviceable.
The investigation
Investigators examined the damaged tail rotor blade to determine the nature of the injury. The analysis revealed that the damage was caused by a high-energy impact with a small, thin, metallic object that struck the blade 'edge-on' while the rotors were rotating. The impact was forceful enough to shear and coil a strip of the blade's leading edge material. While the specific object responsible for the damage could not be identified, the investigation noted that the damage characteristics were consistent with a small, square-faced metal item.
Further examination of the cut revealed forked fatigue fractures originating from the corners of the impact site, with the largest crack reaching approximately 1 cm in length. The extent of these fatigue cracks suggested that the damage had not been present during the earlier flight from Manchester. Although the owner had recently completed construction of a new hangar and landing pad at his home site and had cleared the area of debris, no matching metallic fragments were found during a follow-up search of the premises.