On October 26, 2004, at 0943 eastern daylight time, a Beech BE-200, N888TR, was substantially damaged during landing at the Washington Dulles International Airport (IAD), Dulles, Virginia. The certificated airline transport pilot and the two passengers were not injured. Day instrument meteorological conditions prevailed for the business flight that departed Piedmont Triad International Airport (GSO), Greensboro, North Carolina, destined for Eastern WV Regional Airport (MRB), Martinsburg, West Virginia. An instrument flight rules (IFR) flight plan was filed for the flight conducted under 14 CFR Part 91. According to the pilot, after departing Greensboro, the flight progressed without incident until reaching the Martinsburg area. He then completed several holding circuits to allow the weather to improve. While holding, the pilot checked the automated surface observing system, which reported 1/4 mile visibility in fog, and 100 feet of vertical visibility. After about 20 minutes, the weather seemed to improve, and because the pilot could occasionally see the ground, he requested an approach clearance. The flight was subsequently cleared for the ILS RWY 26 approach. About 50 feet above the decision height, the pilot had the runway environment in sight, and reported that the in-flight visibility was about 1/2-mile. He then maneuvered the airplane, and initiated a flare for landing; however, prior to touching down, the pilot lost all forward visibility and initiated a missed approach. He advanced the power levers, and as the engines responded, he felt the airplane contact "something." The airplane continued to accelerate and climb, but when the pilot selected the landing gear handle to the up position, only the nose wheel and right main landing gear indicators indicated gear up, while the left main landing gear remained in a transient condition. The pilot declared a missed approach and diverted to Dulles. There, he executed a "low-pass" so the tower controller could inspect the landing gear. The controller advised the pilot that it appeared the left landing gear was damaged, and issued a landing clearance. The airplane touched down on runway 1 and began to roll-out, but at approximately 40 knots, the left main landing gear collapsed. The airplane skidded to a stop on the runway, and the pilot, along with the passengers, exited without further incident. According to a Federal Aviation Administration inspector, examination of the wreckage revealed damage to the left engine firewall and forward pressure bulkhead. A weather observation taken about 13 minutes before the accident at the Martinsburg Airport recorded the wind as calm, visibility 1/4 mile in fog, vertical visibility 100 feet, temperature 45 degrees Fahrenheit, dew point 45 degrees Fahrenheit, and an altimeter setting of 30.22 inches of mercury. A witness, who was holding short of runway 26 in a vehicle at Martinsburg, stated that after the pilot of the accident airplane declared a missed approach, he was cleared by the control tower to conduct a runway sweep. During the sweep, forward visibility was limited to "two to three runway lights," which equated to between 400 and 600 feet. About halfway down the runway, the witness found debris from a taxiway sign and various aircraft parts. Because of poor visibility, he could not see the source of the debris, so he parked his vehicle and began to search on foot. He found that a taxiway sign on the left side of the runway had been struck, and there were three tire marks in the grass that paralleled the runway. The marks were approximately 100 feet long, and ended approximately 10 feet past the base of the sign. In addition, the left and center tire marks transitioned over the 6-inch high concrete base the sign was mounted on. According to the instrument approach procedure for the ILS RWY 26 approach at Martinsburg Airport, decision height was 200 feet agl, and required visibility was at least 1/2 mile.