On October 1, 2005, at 1230 Pacific daylight time, a twin engine Beech B-60 (Duke), N924GF, sustained substantial damage following a landing gear collapse during the landing rollout at Arlington Municipal Airport, Arlington, Washington. The airplane, which is registered to Precision Approach Management, LLC, was being operated as a visual flight rules (VFR) cross-country flight under the provisions of Title 14, CFR Part 91, when the accident occurred. The airline transport pilot, the sole occupant of the airplane, was not injured. Visual meteorological conditions prevailed for the cross-country flight that originated at Bellingham, Washington, approximately 30 minutes prior to the accident. In a written statement dated October 11, the pilot reported that he lowered the landing gear before entering the downwind to runway 34. He reported that after the landing, during the rollout, that the landing gear "collapsed and the airplane slid to a stop." A witness reported that the airplane's left wing "dropped" during landing and he heard what was described as the airplane's engines power up, followed by a rapid deceleration of the airplane's engines. The witness reported that as the engines decelerated, the airplane settled to the ground eventually coming to rest on its belly. Airport maintenance personnel reported that the airplane come to rest approximately 3,400 feet beyond the threshold of runway 34, adjacent to the alpha three taxiway. Propeller slashes were observed on the runway surface in three separate locations. The first grouping of slash marks was noted approximately 1,280 feet beyond the landing threshold of runway 34. The second grouping of slash marks (approximately 246 feet in length) was noted approximately 1,720 feet beyond the landing threshold. The third set of slash marks was noted approximately 843 feet south of the wreckage and continued to the point where the airplane came to rest. On February 7, 2006, the NTSB IIC examined the airplane's main landing gear system at the operator's hangar facility in Arlington, Washington. The main landing gear assembly was whole and intact. The forward and aft attach fittings (both left and right) were undamaged and no deformation to the immediate area of the attach points was noted. The outboard landing gear doors were intact and remained attached at their respective mounting points. Nominal damage was noted to the outboard gear door assemblies. The inboard landing gear doors remained attached to the wing assembly, however, both sustained extensive damage. Erosion type damage, to include longitudinal striations, was noted to both doors. Extensive damage was noted to the distal ends of both inboard doors. The outboard section of the left inboard gear door was bent, approximately 45 degrees, in the direction of the gear hinge. The outboard section of the right inboard gear door was curled inboard, opposite the direction of the hinge. The airplane's retractable courtesy step, which actuates simultaneously with the landing gear, was observed in the down and locked position. No damage was noted to the courtesy step assembly. Further examination of the landing gear system revealed bending type deformation to the right side landing gear retraction rod and inboard landing gear door retraction rod. No damage was noted to the left side retraction rods. The operator reported that with the exception of a leaking landing gear strut (left) there were no mechanical malfunctions or failures with the airplane prior to the accident.