On October 28, 1997, at 0938 central standard time, a Pilatus PC-6 airplane, N19TX, was substantially damaged while landing near Lexington, Texas. The commercial pilot and his passenger were not injured. The airplane, owned by 6 individuals, was being operated by Skydive Productions of Plano, Texas, under Title 14 CFR Part 91 at the time of the accident. Visual meteorological conditions prevailed for the business flight which originated from the Lee County Airport, near Giddings, Texas, at approximately 0930. According to the owner of the airplane, "the airplane was being delivered to a new airstrip to start a new skydiving school." The owner added that "the pilot, having flown from Mississippi, cautiously landed at an alternate airfield south of his destination to meet with the airfield manager to see the new airfield." According to the "drop zone manager," a 3,500 foot long by 150 feet wide airstrip was "graded out" an open pasture located 2.1 miles east of Lexington. The pilot of the airplane that was to be used for the school landed at Lee County Airport, located 14 miles south of the new airstrip, where he was picked up by his wife, who had driven the family car from Mississippi. The pilot was then driven to the new airstrip to physically inspect the airstrip prior to his first landing. The drop zone manager added that during the physical inspection and tour of the new airstrip, the pilot drove the entire airstrip. He later joined the drop zone manager and they both walked out to the airstrip, across the runway to the ungraded grass on the opposite side, where the pilot was personally briefed. At this point, the drop zone manager pointed out the tractor lane and swale or draw that run perpendicular to the runway on both sides. The swale or draw consisted of a 12 to 15 foot wide lane which is approximately 10 to 12 inches deep. The drop zone manager stated that the swale was the result of tractor trails left during the grading process of the airfield. While landing to the south in the airstrip's inaugural landing, the pilot lined up to land on the east side of the new runway, and ended up touching down on the unimproved portion of the airstrip. During the landing roll on the unimproved portion of the airfield, while rolling at approximately 25 knots, the landing gear impacted one of the swales the pilot had been briefed on earlier. The right main landing gear collapsed, and the right wing subsequently struck the ground resulting in structural damage to the outer portion of the right wing and the outboard portion of the right aileron. Additionally, the fuselage was reported to be damaged near the wing attaching point. The commercial pilot had accumulated over 400 hours in the airplane. The short takeoff and landing (STOL) airplane was purchased from the Government of Australia and exported to the United States in a non-flyable condition. The airplane had accumulated a total of 9,358 flight hours. Examination of the airplane by FAA inspectors at the accident site confirmed the structural damage. The wreckage of the airplane was examined by the investigator-in-charge (IIC) at Air Salvage of Dallas on November 4, 1997. The severity of the damage incurred by the right main landing gear was found not to be compatible with the physical evidence found at the accident site. The operator, pilot, drop zone manager, and FAA inspector concurred that the failure of the landing gear was not the direct result of impacting a low rise of soft dirt at low speed. The aircraft records were examined to determine if the airplane had any previous damage history. The aircraft records did not reflect any previous accident history or damage that could have led to the failure of the landing gear. The reason for the failure of the right main landing gear could not be determined.