On May 23, 2012, about 1045 mountain daylight time, the pilot of a Rockwell International S-2R, N8421V, made a forced landing in a pasture about 1.5 miles southwest of Howard (K8D9) Municipal Airport, Howard, South Dakota. The pilot, the sole occupant on board, was not injured. The airplane was substantially damaged. The airplane was registered to and operated by East River Air Spray, LLC, Volga, South Dakota, under the provisions of 14 Code of Federal Regulations (CFR) Part 91 as a test flight. Visual meteorological conditions (VMC) prevailed at the time of the accident, and no flight plan had been filed. The local flight originated about 1040. The engine had recently been installed under STC (Supplemental Type Certificate) SA01980CH, and had accrued 2 hours flight time prior to the accident. According to the pilot's statement and accident report, he took off on the test flight and when he adjusted the throttle and propeller control for climb, he noticed low (40 psi, pounds per square inch) oil pressure and a corresponding loss of propeller pitch control. He decided to return to the airport but the airplane started to settle and lose altitude. He barely cleared a power line and fence and made a forced landing in a rough pasture. The right wing struck terrain, damaging the spar, and the airplane nosed down. Postaccident examination revealed a fractured aluminum line where it attaches to the propeller governor. This resulted in a loss of oil and oil pressure. Only 2 quarts of oil remained in the crankcase. The fractured line had been fabricated during the engine installation, and FAA Form 337, dated April 25, 2012, had been filed. Maintenance personnel told FAA inspectors they should have installed more Adel clamps to secure the line and minimize vibrations.