On August 16, 1994, at 1828 eastern daylight time, a Enstrom F- 28A, N13CM, lost partial engine power during cruise flight. The pilot executed a precautionary landing into a field in Stewartsville, New Jersey. During the landing the tailboom was severed. The pilot and two passengers were not injured. Visual meteorological conditions prevailed. The local sightseeing flight departed the Warren County Fairgrounds, Warren County, New Jersey, and was conducted under 14 CFR Part 91. The pilot reported, "Aircraft was over Reservoir when engine began to loose power. Excessive yawing of A/C began." He said he flew the helicopter over a field and began a descent down into the field. The pilot reported, "In my low Recon of these fields I noticed the fields were unimproved and made decision to zero out airspeed prior to touchdown...with tail rotor upslope and near zero airspeed, I leveled A/C and pulled collective to cushion. A/C settled vertically, upon touchdown [main rotor] blade flexed down and cut tailboom off." Postaccident examination of the airframe and engine did not reveal any anomalies. The engine was started and ran with no anomalies noted. (See attached Inspector's Statement for details of examination).