On April 11, 2002, at 0800 central daylight time, a Bell 206B helicopter, N513FD, was substantially damaged during a forced landing following a loss of engine power near Walnut Hill, Texas. The helicopter was registered to Heartland Helicopter Leasing of Rogersville, Missouri, and operated by Sky One Helicopters of Fort Worth, Texas. The airline transport pilot and two passengers were not injured, and one passenger sustained minor injuries. Visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 traffic reporting flight. The flight originated from the Dallas Love Field Airport, Dallas, Texas, at 0550.

According to information obtained in the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) the helicopter experienced a "sudden" loss of power while at approximately 400 feet agl. The pilot initiated an autorotation to a residential street. During the forced landing, the main rotor blades struck trees, which over hung the street. Subsequently, the helicopter touched down "hard" and slid to a stop.

An examination of the helicopter, by an FAA inspector who responded to the accident site, revealed that the helicopter's tail boom had separated aft of the horizontal stabilizer, one main rotor blade was damaged, and the landing skids were spread.

Further examination of the helicopter on April 16, 2002, at Air Salvage of Dallas in Lancaster, Texas, under supervision of the NTSB, revealed the B-nut on the PC pneumatic line from the power turbine governor tee fitting to the fuel control, at the fuel control end, was backed off from the fitting. When viewed initially, the B-nut appeared to be connected, but when moved by hand, it dislodged from the fuel control connection. The cushioned clamp on this same line was not fastened to anything. Further examination revealed the engine was void of the required torque striping on all B-nuts. According to the Rolls-Royce Allison 250C20 Series Operation and Maintenance manual, paragraph 9.B., "when proper free state alignment is attained, complete tubing installation by simultaneously securing the coupling nuts. After all B-nuts are properly tightened to the correct torque values, apply a slippage mark (torque paint) of contrasting color approximately 0.063 inch (1.60mm) wide minimum. The mark shall extend down the side of the B-nut and onto the mating fitting. Install necessary clamping."

Examination of the maintenance records revealed the helicopter accumulated 42.6 hours since the last 100-hour maintenance inspection that was performed on March 29, 2002.

The required inspections of this system are noted in table 602 of the Rolls-Royce Allison 250C20 Series Operation and Maintenance manual, under the "100 hour inspection checklist" section, it is noted to "inspect all "B" nuts for application and alignment of torque paint. If missing, loosen "B" nut, retighten, and apply torque paint." Also indicated in the Bell 206B Flight Manual, section 2, during the exterior preflight, the pneumatic lines should be checked for overall condition and security.

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