On April 26, 2000, at 1350 central daylight time, a Cessna 140, single-engine airplane, N76176, struck a fence during a forced landing following a loss of oil pressure near Hunter, Oklahoma. The airplane was owned and operated by the private pilot. The private pilot, sole occupant, was not injured, and the airplane sustained substantial damage. Visual meteorological conditions prevailed for the cross-country flight, and a flight plan was not filed. The 14 Code of Federal Regulations Part 91 personal flight departed Justin, Texas, at 1020, with a planned destination of Des Moines, Iowa. The pilot reported on the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) that the flight was en route when the oil pressure started to decrease. The pilot shut down the engine and picked a field for the landing. Prior to the touchdown, the pilot saw a fence in the center of the field. The main landing gear struck the fence, and the airplane flipped to the inverted position. The FAA inspector responding to the accident site found the airplane (36 degrees 33 minutes north; 097 degrees 24 minutes west) approximately 50 feet north of the fence. The inspector and the pilot found oil covering the lower surface of the airplane from the engine cowling to the empennage. The FAA inspector stated that the "oil cap was not found at the site." The pilot stated that he thought the oil cap was on during the preflight and came off in-flight. Structural damage was found at the engine mount, right wing strut, and the vertical stabilizer. On the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2), the pilot stated that the oil cap was lost in flight. He recommended "safety A.D. [airworthiness directive] on all oil caps." The pilot reported to the NTSB investigator-in-charge that the oil cap did not have a retainer safety chain. He stated that he had put the oil cap on this make and model of aircraft hundreds of times in his history of flying. The Teledyne Continental engine and Cessna Aircraft Company representatives reported that the manufacturers did not have any history where a secured oil cap came off in flight. The aircraft representative further stated that if the "tabs inside the filler cap became corroded completely through, they would not retain the cap properly." A mechanic, who recovered the airplane from the field, stated that the oil cap was not found. He further stated that he did notice any discrepancies or rust on the oil filler neck. The manufacturer's preflight checklist states in part: A. BEFORE ENTERING THE AIRPLANE (1) Check oil level. The operating details states in part: Oil Level: The quantity can be checked easily by raising the hood on the right side and reading the quantity in the sump directly on the stick attached to the oil tank cap. In replacing the cap, make sure that it is on firmly and turned all the way to the stop at the right to prevent loss of oil through the filler neck.