What happened
On 20 March 2008, an Agusta Westland A109E, registration EI-SBM, was conducting a private flight from Celtic Heliport to Weston Airport. While flying near Dunshaughlin, the pilot reported a mechanical issue and issued a "MAYDAY" call. The aircraft experienced a sudden, violent loss of directional control, characterized by a dramatic yaw and pitch.
As the helicopter's airspeed dropped, the pilot was unable to maintain control and initiated an emergency autorotation to avoid built-up areas. The aircraft entered a rapid spin and struck the ground in a boggy area near Lagore. The helicopter sustained substantial damage, and the pilot sustained serious injuries to his back. Due to the difficult terrain, the pilot had to be airlifted by the Irish Coastguard.
The investigation
Investigators examined the wreckage and discovered that the tail rotor drive-shaft had completely severed just forward of the second bearing. This breakage had disconnected the drive to the tail rotor gearbox. Upon inspecting the shaft, investigators found a piece of cleaning cloth material entangled on the long tail rotor drive-shaft between the first and second bearings.
Further examination of maintenance records revealed that the aircraft had recently undergone a 12-month inspection and had received new engine fire bottles on the morning of the accident. While the maintenance organization stated they did not open the tail rotor drive-shaft cover, the investigation noted that the required procedure for replacing the fire bottles actually necessitates opening that specific cover. The investigation could not definitively prove how the cloth entered the area but suggested it likely originated from the maintenance organization's supplies.
Findings
- The primary cause of the accident was the fatigue and failure of the long tail rotor drive-shaft.
- This failure was directly induced by a cleaning cloth that had become wrapped around the shaft, creating out-of-balance forces.
- The loss of directional control became unrecoverable once the aircraft's airspeed decayed below 60 knots.
- The presence of the cloth in the drive-shaft area was likely the result of systemic and human error during maintenance or inspection processes.