DEN08LA138
DEN08LA138

On August 11, 2008, approximately 1530 central daylight time, a Bell 206L-1 single-engine helicopter, N832AH, sustained substantial damage during a forced landing following a partial loss of engine power while maneuvering near Heber Springs, Arkansas. The airline transport pilot, who was the sole occupant, was not injured. The helicopter was registered to and operated by Hillsboro Aviation Inc., Hillsboro, Oregon. Visual meteorological conditions prevailed, and a flight plan was not filed for the Title 14 Code of Federal Regulations Part 133 external load flight. The flight departed a remote heli-spot location approximately 20 minutes prior the accident.

According to the operator, the helicopter had been conducting external load operations on the day of the accident and had just departed after refueling. While transporting an empty container on the long line at 300 feet above ground level, the engine "spooled down". The pilot released the external load, executed a 180-degree turn and autorotation. During the forced landing, the helicopter landed hard in a tree farm and impacted trees, rolled over and came to rest on its right side. The pilot shut off the fuel and exited the helicopter. Examination of the helicopter revealed the tail boom was separated, the main rotor blades were bent, and the right side of the fuselage was damaged.

A Federal Aviation Administration inspector, who spoke with a company mechanic, reported that a PC line B-nut was found disconnected on the Rolls Royce 250-C30P engine. The mechanic reported that the last engine maintenance which involved the removal and reinstallation of the PC line was 67.1 hours prior, during a scheduled turbine change. No slippage marks (torque paint) were noted on the fitting.

According to the Rolls Royce 250-C30 Series Operation and Maintenance manual, section 72-00-00, "Proper tightening of engine tubing connections is critical to flight safety...Tubing B-nuts used in installations exposed to a high degree of vibration and pressure surges are subject to torque relaxation when improperly tightened...Old slippage marks (torque paint) shall be completely removed, using torque paint remover, and reapplied each time the B-nut is tightened."

In 1990 (Revision 1, dated February 5, 2007), Rolls Royce issued an "Alert Commercial Service Letter: Maintenance Warning - External Lines". The letter background states that Rolls Royce continues to be involved in investigations of aircraft accidents and incidents which are attributed to improper alignment, clamping, and torquing of engine tubing during installation. The letter documents examples and causes of the failures of tube assemblies.

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