CEN12LA289

The helicopter, which had been based at sea level, had recently been sold, and the flight instructor and a commercial pilot were flying it across the country to its new base. While in cruise flight over mountainous terrain at high density altitude, the flight instructor initiated a practice autorotation for the purpose of maintaining proficiency. During the autorotation, the engine stopped producing power. The instructor continued the autorotation to a landing; however, during the landing, the main rotor blades severed the tail boom. A postaccident engine run at high density altitude revealed that the engine ran rough at an idle power setting with a full rich fuel mixture. Leaning the fuel mixture improved engine performance. It is likely that the fuel control unit was set by maintenance personnel to provide a rich mixture at sea level, which resulted in poor engine performance at high density altitudes.

On May 10, 2012, about 1015 mountain daylight time, a Robinson R44 II helicopter, N7523S, performed an autorotation following a loss of engine power near Grants, New Mexico. The certificated flight instructor (CFI) and commercial pilot were not injured and the helicopter was substantially damaged. The helicopter was owned and operated by iPrerogative Inc, Washington, Utah, under the provisions of 14 Code of Federal Regulations Part 91 as a positioning flight. Visual meteorological conditions prevailed for the flight which operated on a visual flight rules flight plan. The helicopter departed the Albuquerque International Airport (KABQ), Albuquerque, New Mexico, about 0900, and was destined for the Page Municipal Airport (KPGA), Page, Arizona. According to a statement provided by the CFI, while cruising over mountainous terrain, at 10,000 feet mean sea level (msl), the CFI slowed the helicopter to 70 knots and initiated a practice autorotation, in order to maintain autorotation proficiency. The pilot reported checking 80 percent engine rpm at least twice during the practice autorotation. About 9,200 feet msl (about 600 feet above ground level), the CFI attempted to restore engine power but the engine had quit producing power which was verified by the engine tachometer. The pilot continued the autorotation and lined up with the best available landing area and landed. On touchdown, the helicopter’s main rotor blade contacted the tail boom severing the tail boom. Substantial damage was sustained to the main rotor blades, tail boom, and tail rotor blades. A postaccident engine run was conducted by the National Transportation Safety Board and a technical representative from Lycoming Engines. The engine started and ran for several minutes; however, the engine occasionally ran rough at idle power with a full rich mixture setting. Leaning the fuel mixture via the cockpit mixture control improved engine performance. The density altitude at the time of the engine run was approximately 8,100 feet. A review of maintenance records showed that maintenance work was performed in Florida at an altitude of 100 feet mean sea level. Any adjustment to the fuel control unit, which sets the idle mixture, would have been set at this altitude by maintenance personnel.