On Sunday, October 24, 1993, at 1030 eastern daylight time, a Piper PA-602P, N6891M, registered to and piloted by Steven E. Lynn, sustained substantial damage while taxiing for takeoff at the Rough River State Park Airport, Falls of Rough, Kentucky. The pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed. The flight was operating under 14 CFR 91. The pilot was back taxiing on runway 20, in preparation for takeoff on runway 02. There was no control tower at this airport, so he made radio calls on the airport frequency stating his intentions. He stated that after he taxied onto the runway, he observed an airplane on final approach for that runway. He made a radio call requesting the airplane to go-around. The airplane did not respond to this call, so the pilot of N6891M taxied off the runway surface onto the grass. The terrain was soft, and as he attempted to taxi back onto the paved runway, the right landing gear collapsed, penetrating the wing and damaging the main wing spar. Mr. Nick F. Weber, Aviation Safety Inspector for the Federal Aviation Administration, conducted an examination of the airplane and interviewed the pilot and a witness. In his report, Mr. Weber stated: According to the pilot, the aircraft had taken runway 20 to back taxi for takeoff when he noted another aircraft approaching on short final for landing. N6891M departed the runway onto the adjacent soft turf...When the pilot attempted to taxi back onto the runway, the right main gear collapsed, damaging the right wing spar... Mr. Weber's report continued: A witness...stated that he saw N6891M take the runway for takeoff. He also saw a light twin- engine aircraft on short final. N6891M immediately departed the runway onto soft sod...