On September 6, 1995, at 1147 central daylight time, a Piper PA- 28R-180, N3726T, was substantially damaged during a forced landing near Lago Vista, Texas. The flight instructor, the pilot receiving instruction, and a passenger sustained minor injuries. The flight originated at the Bridgeport Municipal Airport, near Bridgeport, Texas, at approximately 1015 CDT. Visual meteorological conditions prevailed for the instructional flight for which a composite VFR/IFR flight plan was filed. According to Austin Approach Control, the airplane was assigned 4,000 feet MSL while receiving radar vectors for a practice ILS approach to the Robert Mueller Municipal Airport, in Austin, Texas. The flight instructor reported a loss of engine oil pressure, accompanied by a vibration and an increase in cylinder head temperature when the flight was approximately 15 miles northwest of Austin, Texas. The flight instructor turned the airplane towards the nearest available airport, and notified approach control of the situation. Approach control issued vectors and distance to the Rusty Allen Airport, near Lago Vista, Texas. The airport is located in hilly terrain, and is surrounded by trees. The pilot stated that he did not have sufficient altitude available to align the airplane with the runway, so he elected to land perpendicular to the runway. The airplane touched down approximately 40 feet to the north of Runway 15, continued downslope, went through a fence, and came to rest in a sandy area adjacent to the hangars. The right wing separated from the airframe, and the left wing was deflected upwards 90 degrees. Examination of the engine by the owner's representative revealed that the connecting rods for the #1 and #2 cylinders had separated for undetermined reason.