CEN09LA558

During cruise flight in a reciprocating single-engine helicopter, the pilot heard a loud noise and felt a vibration. The pilot immediately entered an autorotation and turned the flight controls over to the flight instructor. The flight instructor elected to continue the autorotation to an open field. During the landing the helicopter's landing skids stuck into the soft terrain, causing the helicopter's nose to pitch down and tail to pitch up. The main rotor blades impacted the tail boom, severing it; the helicopter subsequently rolled onto its side. An examination of the helicopter failed to find a reason for the noise and vibration.

On September 2, 2009, approximately 1040 central daylight time, a single-engine, Hughes 269 helicopter, N58163, was substantially damaged during a landing after entering a precautionary autorotation. The pilot and flight instructor, were not injured. The helicopter was registered and operated by a private individual. Visual meteorological conditions prevailed and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 cross-country flight. In a statement submitted by the flight instructor, he reported that while in cruise flight, they heard a loud noise and the pilot immediately entered an autorotation. During the autorotation, the pilot relinquished the flight controls to the flight instructor. The flight instructor elected to continue the autorotation to a field. The instructor added that during the touch-down, the right front skid "sunk into the soft field", the helicopter's nose dropped and when the tail section rose, the main rotor blades severed the tail-boom. The helicopter subsequently rolled onto its side. The pilot stated that, "they heard and then felt a vibration and a loud bang or explosion" that came from the aft section of the helicopter and so he entered an autorotation. A Federal Aviation Administration (FAA) inspector, who responded to the site, reported that the helicopter's main rotor blades severed the tail-boom during the landing. An examination of the helicopter was conducted by an FAA inspector and a technical representative from the airframe manufacturer. During the inspection the engine was started and ran normally. The transmission rotated with oil visible in the sight gauge. The drive system's "V-belts" appeared undamaged and functional; the clutch actuator operated when electrical power was applied. The engine's lower coupling to lower pulley driveshaft was intact and the splined fittings were undamaged. The helicopter's cyclic and collective controls exhibited continuity through the range of motion. The main and tail rotor blades were examined; the tail rotor blades appeared undamaged. The main rotor blades displayed various degrees of damage, consistent with a sudden stoppage at low rotor RPM and blade impact with the tail-boom and ground. The reason for the loud noise and vibration was not found.