On July 2, 1999, at 1103 central daylight time, a Beech 58, N3240R, piloted by a private pilot, sustained substantial damage during a wheels-up landing on runway 16 (5,001 feet by 100 feet, dry asphalt) at Palwaukee Municipal Airport (PWK), Wheeling, Illinois. Visual meteorological conditions prevailed at the time of the accident. The flight was operating under the provisions of 14 CFR Part 91 and was not on a flight plan. The pilot reported no injuries. The flight departed Three Lakes Municipal Airport, Three Lakes, Wisconsin, at approximately 0945, en route to PWK. In a written statement, the pilot reported, "...Palwaukee gave me a straight in approach for runway 16 and to notify the tower 2 miles out. I flew to the left to line up with 16 and began a slow decent to traffic pattern altitude. About 3-1/2 miles out the tower cleared me to land. I began my pre landing checklist however I became distracted by what I thought was the collision avoidance equipment but in reality was my gear warning horn. There were a couple of aircraft showing up about a mile and a half away and I was looking for them and never completed the checklist and my normal prelanding GUMPS check. The aircraft landed gear up in the center of the runway and slid for a short distance. It stopped half off the left side of runway 16 however no lights were hit." Federal Aviation Administration Advisory Circular 20-34D, Prevention of Retractable Landing Gear Failures, section 4. Operational factors and percentages involved in retractable gear aircraft accidents" as: a. Neglected to extend landing gear - 35.8 percent. b. Inadvertent retraction of landing gear - 10.3 percent. c. Activated gear, but failed to check gear position - 11.3 percent. d. Misused emergency gear system - 0.9 percent. e. Retracted gear prematurely on takeoff - 2.8 percent. f. Extend gear too late - 1.8 percent. Section 5(a)(1) states, "On the downwind leg, or at the final approach fix inbound, make it a habit to complete the recommended landing gear checklist for your aircraft...". Section 5(b)(3) states, Be familiar with the landing gear warning horn and warning light systems of your aircraft. Use the horn system to cross-check the warning light system when an unsafe condition is noted.".