On January 26, 2004, at 1545 Pacific standard time, a Bell 206B, N92CA, registered to and operated by Reforestation Services Inc., as a 14 CFR Part 91 personal proficiency flight, experienced a partial loss of engine power followed by an autorotation to a field near Turner, Oregon. After touchdown, the main rotor blades contacted and severed the tailboom. Visual meteorological conditions prevailed at the time and a company visual flight rules flight plan was in effect. The helicopter was substantially damaged and the commercial pilot, the sole occupant, was not injured. The flight departed from Salem, Oregon, about 30 minutes prior to the accident. During a telephone interview, the pilot reported that he was practicing maneuvers with a 100-foot long line attached in preparation for a check ride the following day. The pilot reported that he was in a hover with the hook at the end of the line just touching the ground. The pilot then increased altitude and raised the hook off the ground about 10 feet, when the engine suddenly decreased power to idle. The pilot immediately initiated an autorotation to an open field. The helicopter subsequently touched down tail low, followed by the main rotor blades contacting and severing the tailboom. The wreckage was recovered from the field and transported to the operator's base of operations in Salem, Oregon. A Federal Aviation Administration (FAA) Inspector from the Hillsboro, Oregon, Flight Standards District Office (FSDO), inspected the engine and found that the fuel nozzle screen was collapsed. Fuel samples were taken from the airframe filter bowl, and the fuel tank. It was visually noted that contaminants were present in the airframe filter bowl. These samples, along with the wetted fuel nozzle screen, and airframe filter were sent to the National Transportation Safety Board Investigator-in-Charge. The pilot reported to the FAA Inspector the he did drain the fuel from the airframe fuel filter during the preflight, but did not note any water or contaminants. Arrangements were made to remove the engine for transport to Rolls-Royce, Indianapolis, Indiana, for engine inspection and test cell run. The fuel samples and fuel nozzle screen and filter were sent to a Federal Aviation Administration Inspector from the Indianapolis FSDO. This inspector oversaw the testing of the engine and components. The engine was visually inspected for preparation of an "as received" engine run. During the inspection, fuel samples were taken from the fuel pump filter bowl and the fuel nozzle supply line. The fuel pump filter bowl contained 20 ml of liquid. 3 ml of brownish/tan liquid separated to the bottom of the sample container. 5 ml of liquid was drained from the nozzle supply line. This fluid was clear. The samples from both sources had an aroma consistent with the smell of paint thinner. The samples were tested and found that the fuel, later determined to be Kerosene (K-1), contained both water and bacteria. There was also Diethylene Glycol Methyl Ether (DIEGME), a fuel additive used as an icing inhibitor was present. The Rolls-Royce representative reported that K-1 is not approved fuel for this engine. The collapsed fuel nozzle screen was inspected for the presence of contaminants. The contaminants noted on the collapsed fuel nozzle screen were found to be brass, oxidized aluminum, pure nickel and aluminum alloys. The engine was placed in a test cell. The collapsed fuel nozzle screen was replaced with a new screen for the test run. The engine was started and warmed up before acceleration to full RPM. Two-aborted wave off's were made and smooth movements of the governor actuator were made. In both tests, the engine controls (fuel control and governor) showed no discrepancies. The engine was accelerated and power calibration readings were taken. The results indicated that the engine was -18.3 at take off horsepower and -20.5 at normal cruise power setting and 402 and 400 shaft horsepower. Normal rated shaft horsepower is 420. The engine was then shutdown and removed from the test cell. Further bench testing to measure the fuel flow and fuel pressure indicated that there were no significant differences during testing of the collapsed fuel nozzle and screen versus a new fuel nozzle and new screen. At the request of the owner's representative, the engine was returned to Standard Aero Limited, Richmond, B.C. on April 2, 2004.