On June 4, 2002, approximately 2200 central daylight time, a Beech BE-100-A100 twin-engine airplane, N799DD, registered to and operated by Finkbeiner Aviation of Little Rock, Arkansas, was substantially damaged when its main landing gear collapsed while landing on runway 18 at Adams Field Airport, Little Rock, Arkansas. The airline transport rated pilot and his pilot-rated passenger were not injured. Visual meteorological conditions prevailed and flight plan was not filed for the Title 14 Code of Federal Regulations Part 91 personal flight. The local flight originated at 2200 from Adams Field. According to information provided in a telephone interview and the enclosed NTSB Pilot/Operator Accident Report (NTSB Form 6120.1/2), the pilot was on a practice approach when he extended the landing gear. The cockpit landing gear indicators yielded "two" green indications. A go-around was performed and the gear cycled several times with no results, including an attempt to use the emergency extension system. Two confirmation passes were performed, and it was confirmed that the left main landing gear was retracted with the nose and right main landing gear extended. After touch down on the right side of the runway, the aircraft exited the left side of the runway resulting in structural damage to the fuselage belly. Examination of the aircraft revealed that left gear extension push/pull tube was found without the lock pin in its clevis. The pin was found in the belly of the aircraft but no nut and washer was found. The aircraft had recently come out of a maintenance facility where the landing gear was worked on.