Bell 206L-1 LongRanger, Heber Springs, Ark., Aug. 11, 2008–The NTSB determined the probable cause of the forced landing by the Hillsboro Aviation LongRanger following loss of power was improper installation of the PC line on the Rolls-Royce 250-C30P engine, which resulted in a partial loss of power. The uninjured ATP-rated pilot, the sole occupant, was moving an empty container on the long line at 300 feet agl, when the engine “spooled down.” The pilot released the external load, made a 180-degree turn and autorotated. During the forced landing, the helicopter landed hard in a tree farm, rolled over and came to rest on its right side.
Examination showed that the PC line B-nut was disconnected. (The PC line is a reference source of compressor discharge pressure to the fuel controller.) Maintenance performed 67.1 hours before the accident involved the removal and reinstallation of the PC line. Investigators found no slippage marks (to visually indicate a change in nut position) on the fitting. According to the Rolls-Royce Operation and Maintenance manual, “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.”