On September 30, 1999, at 0700 mountain daylight time (mdt), a Piper PA-28-181, N3889F, operated by a commercial pilot, sustained substantial damage when the airplane's right wing struck a fence post, during a precautionary landing on a dirt road, 10 miles southwest of Hermosa, South Dakota. Preceding the precautionary landing, the airplane experienced an intermittent loss of engine power while in cruise flight. Visual meteorological conditions prevailed at the time of the accident. The ferry flight was being conducted under 14 CFR Part 91. There was no flight plan on file. The pilot reported no injuries. A pilot-rated passenger, on board, received minor injuries. The cross-country flight originated at Casper, Wyoming, and was en route to Rapid City, South Dakota. In his written statement, the pilot said that while en route to Rapid City, the airplane's engine started to lose power. "After an emergency flow check, I discovered the fuel selector was in the off position. I then realized that I did not switch the ferry tank valve to the off position before taking off from Casper." The pilot switched the fuel selector to the left wing tank, and switched the ferry tank to "off". The engine began to run normally. The pilot said that 15 minutes later, the engine began to lose power again. The pilot turned the fuel selector to the right wing tank, turned on the electric fuel pump, and selected carburetor heat. None of these actions had any effect on the situation. The pilot decided to perform an emergency landing to a dirt road. After touching down on the dirt road, the airplane's right wing tip struck a wood fence post. The impact tore off the right wing and the airplane spun around 180 degrees before coming to a stop. A Federal Aviation Administration (FAA) inspector examined the airplane at the accident site. The airplane rested upright on a dirt road flanked by fences on both sides. The airplane's right wing was broken off at the wing root. The bottom of the fuselage and the elevator showed scrapes and buckles. The propeller blades were bent aft. Examination of the airplane's fuel tanks revealed fuel in the wing tanks and no fuel in the ferry tank. Flight control continuity was confirmed. Examination of the engine, engine controls and other airplane systems revealed no anomalies.