FTW97TA154

The pilot reported that while flying at an altitude of about 35 feet AGL and 30 knots, 'a slight shudder was felt in the helicopter as though a change of wind direction had occurred.' All instruments and systems 'remained in the green and functioning.' Several minutes later, a complete loss of engine power occurred. The pilot recalled hearing a 'strange noise' immediately preceding the loss of power. Subsequently, he initiated a low altitude auto rotation. Approximately 10 feet AGL, the helicopter began to turn to the left, and 'in order to avoid a roll over,' the pilot lowered the collective and informed the passenger of an immanent hard landing. During contact with the ground, the main rotor contacted and severed the tail boom. Immediately following the hard landing, a fire started in the engine compartment. Both the pilot and passenger evacuated, and the helicopter was consumed by fire. Examination of the wreckage to discover the cause of the loss of engine power was unsuccessful due to extreme fire damage to the engine, fuel system, and accessories. The ambient temperature and dew point were conducive to carburetor icing.

On April 7, 1997, approximately 0815 central daylight time, a Bell TH-13T helicopter, N74HL, owned and operated by the pilot, was destroyed following a loss of power and subsequent forced landing near Capitan, New Mexico. Both occupants, the commercial pilot and one passenger, were not injured. Visual meteorological conditions prevailed for the Title 14 CFR Part 91 predator control flight. A flight plan was not filed. The helicopter was airborne for approximately 45 minutes prior to the accident.

The pilot reported that while flying at an altitude of about 35 feet AGL and 30 knots, "a slight shudder was felt in the aircraft as though a change of wind direction had occurred." All instruments and systems "remained in the green and functioning." Several minutes later, a complete engine failure occurred. The pilot recalled hearing a "strange noise" immediately preceding the loss of power. Subsequently, he initiated a low altitude auto rotation. Approximately 10 feet AGL, the aircraft began to turn to the left, and "in order to avoid a roll over", the pilot lowered the collective and informed the passenger of an immanent hard landing. Upon contact with the ground, the main rotor contacted and severed the tail boom. Immediately following the hard landing, a fire started in the engine compartment. Both the pilot and passenger evacuated and the aircraft was consumed by fire.

Examination of the wreckage to discover the cause of the loss of engine power was unsuccessful due to extreme fire damage to the engine, fuel system, and accessories. However, according to the helicopter manufacturer, who assisted in the examination, the post impact fire most likely resulted from the right, external mounted, fuel tank breaking loose from its mounts and dislodging the fuel lines. This allowed fuel to spill onto the hot engine exhaust manifold. The helicopter was not equipped with fiberglass fuel tank straps or self sealing "break away" fuel line fittings.

According to carburetor icing probability charts, the ambient temperature and dew point were conducive to carburetor icing.