On September 16, 2006, about 1400 mountain daylight time, an Amorde Glasair II-S RG, N183TA, sustained substantial damage subsequent to a hard landing on runway 16 at the Rockford Municipal Airport, Rockford, Idaho. The airplane is owned by the pilot, and was being operated as an instrument flight rules (IFR) cross-country flight under the provisions of Title 14, CFR Part 91. The commercial pilot, the sole occupant of the airplane, was not injured. Visual meteorological conditions prevailed at the accident airport. The flight originated from Bozeman, Montana, at 1245 mountain daylight time. The pilot's planned destination was Twin Falls, Idaho. In a written report to the National Transportation Safety Board, the pilot reported that during cruise flight he noticed the aircraft's left wingtip fuel cap was missing. He stated fuel was not venting from the tip tank, however the airplane was accumulating ice and he was concerned that ice would collect over the open fuel port and potentially contaminate the fuel system. The pilot reported the aircraft continued to accumulate ice and eventually the airspeed indicator dropped to "zero" and the angle of attack indicator froze. The pilot declared an emergency and ultimately requested landing at the nearest airport, which was approximately 10 miles from his position. The pilot reported that as he "bleed airspeed off" for landing, approximately 5 feet above the runway, the airplane "pitched forward and dropped to the runway." The airplane bounced and eventually came to rest off the runway. The main landing gear collapsed during the runway excursion. The pilot reported the runway was 2,800 feet in length and the winds were from 180 degrees at 14 knots, gusting to 20 knots. The temperature at the airport was approximately 50 degrees F.