EL PASO, TX, USA
N6187Y
Hughes OH-6A
The helicopter's engine experienced a partial loss of engine power while maneuvering at 60 feet agl and a forward airspeed of approximately 10 knots. In response to the loss of engine power, the pilot 'increased power, pulled up on the collective, in order to increase airspeed.' The engine immediately began to 'coast down.' The pilot added that due to the relatively low altitude, slow airspeed, and insufficient rotor rpm available for the autorotation, the helicopter landed hard. Examination of the engine revealed that a power control (PC) line, which ran between the fuel control unit and governor, had separated. Metallurgical examination revealed that the PC line failed due to fatigue. A bend in the line was observed at the location corresponding to the base of the ferrule at the failed end, indicating that excessive force may have been used during installation of the line. It is likely that fatigue initiated due to the additional stresses placed on the tube by this bend.
On April 13, 2000, at 1120 central daylight time, a Hughes OH-6A helicopter, N6187Y, was substantially damaged during a hard landing following a loss of engine power near El Paso, Texas. The commercial pilot, sole occupant of the helicopter, sustained minor injuries. The helicopter was registered to and operated by the U.S. Border Patrol Air Operations, El Paso, Texas. Visual meteorological conditions prevailed for the 14 Code of Federal Regulations Part 91 public use flight, for which no flight plan was filed. The local flight originated from the El Paso International Airport, El Paso, Texas, at 0900. According to the pilot, the helicopter experienced a partial loss of engine power during a patrol mission while maneuvering at 60 feet agl and "moving forward at an airspeed just below effective translational lift, approximately 10 knots." In response to the loss of engine power, he "increased power, pulled up on the collective, in order to increase airspeed." The engine immediately began to "coast down." The pilot initiated an autorotation and made a turn to the left, with the intent to land on a gravel road. He stated that due to the relatively low altitude, slow airspeed, and insufficient rotor rpm available for the autorotation, the helicopter landed hard and came to rest upright. Postaccident examination of the airframe revealed that the tailboom separated from the helicopter. One main rotor blade separated from the main rotor hub and the skids were spread. Additionally, examination of the Allison C20B turboshaft engine revealed that a power control line (PC line), which ran between the fuel control unit and governor, had separated. The PC line was examined at the NTSB Materials Laboratory in Washington, D.C. The line separated at the base of the flange portion of the line. A slight bend was observed .375 inch from the base of the flange. A circumferential impression was observed at the inner radius of the bend. The location of the impression corresponded with the end of the ferrule when properly assembled. The fracture surface on the flange portion was examined utilizing a scanning electron microscope. Two areas were observed which exhibited features consistent with fatigue.
The failure of the pilot to maintain rotor rpm during an autorotation, which resulted in a hard landing. A factor was the partial loss of engine power resulting from the separation of the power control line due to fatigue, as a consequence of improper installation.
Source: NTSB Aviation Accident Database
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