On March 5, 2005, approximately 1715 central standard time, a Piper PA-23-250 twin-engine airplane, N33AC, registered to and operated by the pilot, was substantially damaged when the right main landing gear collapsed during the landing roll at the Westport Airport (4F1), near Westport, Oklahoma. The private pilot, sole occupant of the airplane, was not injured. Visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 personal flight. The local flight originated from 4F1 approximately 1600. The 5,500-hour pilot reported in the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) that during the landing roll on runway 3 (2,900-foot long and 42-foot wide asphalt runway), the right main landing gear collapsed. Subsequently, the airplane veered to the right, exited the runway, and traveled down a 12-foot rock embankment, striking multiple small trees. The airplane came to rest upright approximately 60 feet to the right of the runway. Examination of the airplane by an Federal Aviation Administration Inspector (FAA), who responded to the accident site, revealed that the left wing was partially sheered-off at the wing root. The trunk of a tree was found embedded in the leading edge of the right wing. Further examination showed that the right main landing gear Torque Link Assembly P/N 31805-06 (scissors assembly) was missing the following: bolt (P/N 751 370), cotter pin (P/N 424 052), castle nut (P/N 404 101), washer (P/N 407 565), and bushing (P/N 751 367). The last annual inspection was completed on May 20, 2004, about 45.6 hours prior to the mishap.