Incident Overview
On September 12, 2014, at approximately 1115 mountain standard time, a Bell 206L4 helicopter, registration N64AW, experienced a partial loss of power and made a forced landing onto a gravel road near Tombstone, Arizona. The helicopter was operated by Airwest Helicopters LLC under 14 CFR Part 135. The commercial pilot and one passenger were uninjured. The helicopter sustained substantial damage to the tailboom. Visual meteorological conditions prevailed, and a company visual flight rules flight plan was filed. The flight originated from Sierra Vista Municipal Airport – Libby Army Airfield (FHU) at 1050 for a local flight.
Pilot Report
The pilot reported that about 20 minutes into the flight, he started a climb at approximately 60 knots indicated airspeed (KIAS). When torque reached 85%, he observed power turbine RPM (N2) and main rotor RPM (Nr) at 95%. Turbine outlet temperature (TOT) was about 680 degrees; other indications were normal. The pilot reduced collective until N2/Nr returned to 100%; torque was about 60%. He increased power to 70% torque, and N2/Nr decreased to 95%. Lowering collective a second time restored N2/Nr to 100%. The pilot selected a suitable landing site and descended at about 70 KIAS while maintaining 95% N2/Nr at about 40% torque. When approximately 60-70 feet above the ground, he decelerated; the helicopter descended rapidly and impacted hard. Subsequently, the main rotor blade severed the tailboom.
Postaccident Examination
The engine was removed and transported for an engine run. Before start, a pressure air leak check revealed three air leaks at separate "B" nut fittings: two at the power turbine governor and one at the gas producer fuel control. The engine was started and operated, but experienced a power loss similar to the pilot's description. After shutdown, the "B" nut fittings were examined. One "B" nut was less than finger tight, a second was just above finger tight, and the third had breakaway torque within specification. All fittings displayed a torque stripe and had visible cracks in the paint between the "B" nut and fitting.
The three "B" nuts were torqued to specifications. One leak persisted; the line was removed and found to have a bend near the end. A new line was installed, torqued, and checked. No leaks were observed, and a subsequent engine run showed normal operation with no anomalies.
Maintenance Background
Review of maintenance logs showed the most recent 100-hour inspection was completed on July 11, 2014, at 4230.8 hours total time. The accident occurred about 66 hours later, at 4,297 hours total time. Rolls-Royce has issued several Commercial Service Letters since September 1987 addressing improper torque or alignment of fuel, lube, and air system tubes and fittings. These service letters highlighted commonly seen issues and urged compliance with appropriate manuals. They also issued placards, warning labels, and recommended maintenance checks every 100 hours.