What happened
On 13 October 2006, a Eurocopter EC120B, registration N526AG, was conducting a private flight from Carlow to a landing site at Tougher Business Park, near Newbridge. The pilot, who was familiar with the grass landing area, arrived at a hover position east of the intended site. At this time, the pilot observed a second helicopter, a Hughes OH-6A, registration N239MY, parked on the ground with its main rotor nearly stationary.
As the pilot of N52ly6AG maneuvered to land, the aircraft passed in close proximity to the left side of the parked Hughes OH-6A. The pilot of the stationary aircraft had already exited his cockpit and attempted to wave off the approaching helicopter. However, the intense rotor downwash generated by the maneuvering Eurocopter EC120B caused the blades of the parked Hughes OH-6A to move. Because the Hughes OH-6A was not equipped with a rotor brake, the downwash forced a main rotor blade to flap downward, resulting in a strike against its own tailboom. There were no injuries to either pilot, but the impact caused damage to the tailboom, a main rotor blade, and the rotor damper.
The investigation
The AAIU investigation focused on the mechanics of the rotor movement and the proximity of the two aircraft. Investigators established that the Hughes OH-6A was subject to significant aerodynamic forces from the passing aircraft. The investigation also verified the licensing of both pilots, confirming that the pilot of the US-registered N526AG was properly licensed to operate the aircraft within Ireland using a UK-issued license. Additionally, the investigation looked into the ownership structure of the aircraft, noting the use of a UK-based trustee to facilitate US registration for a non-US citizen.
Findings
- The primary cause of the damage was the proximity of the maneuvering helicopter to the stationary aircraft.
- The rotor downwash from the Eurocopter EC120B was sufficient to deflect the blades of the parked Hughes OH-6A.
- The Hughes OH-6A was particularly vulnerable to such forces because its main rotor was not secured with a rotor brake, allowing the blades to rotate and flap freely in response to the wind.
- The pilot of the maneuvering aircraft failed to maintain adequate clearance from the parked helicopter during the landing approach.