HISTORY OF FLIGHT On June 9, 2008, about 1130 central daylight time, an amateur-built Avid Mark IV Aerobat, N652DM, was substantially damaged while landing at Ruckle Airport (FL17), Niceville, Florida. The certificated airline transport pilot was seriously injured. The flight was conducted under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the local personal flight. The airplane was built, owned and operated by the accident pilot. The pilot was in a coma for several months following the accident, and did not recall the accident. The day before the accident, an aircraft mechanic, with an inspection authorization, witnessed the accident pilot working on the airplane's engine. The pilot told the mechanic that the airplane felt "wobbly" in flight, and that an M8 Allen screw that held the primary gear for the reduction gearbox on the crankshaft, had become loose. The pilot also told the mechanic that the threads were damaged; however, it was unclear if the threads on the bolt or the crankcase were damaged. There were also metal shavings on the magnetic oil plug, but that he felt it would be acceptable to fly without looking for metal shavings inside the engine, since he was only going to remain in the airport traffic pattern. The mechanic saw the accident airplane taxi for takeoff about 1030, but did not hear or see the airplane return. An eyewitness observed the airplane on the downwind, base, and part of the final legs of the airport traffic pattern. She stated that the airplane was flying "just above the tree tops." The airplane turned toward the runway, and then descended below the tree line, and out of the witness' view. She then heard the airplane impact the ground. She also stated that the airplane did not appear to be "out of control." PERSONNEL INFORMATION The pilot held an airline transport pilot certificate, with an airplane multiengine land rating. He also held a commercial pilot certificate, with an airplane single-engine land rating. Additionally, he held a repairman experimental aircraft builder certificate, with an inspection limitation for the accident airplane only. His most recent Federal Aviation Administration (FAA) first-class medical certificate was issued on May 12, 2008. According to the accident pilot, he had accumulated 8,528 hours of total flight experience, and 525 hours of flight experience in the accident airplane make and model. His last flight review was completed on March 8, 2008. AIRCRAFT INFORMATION The two-seat, single-engine experimental airplane, serial number 1108D, was issued an airworthiness certificate in August 1995. The airplane maintenance records indicated that the most recent inspection was completed on May 29, 2008, with a total time in service of 507 hours as of that inspection. The records indicated at that time, the wheel bearings and the fuel line from the wing tank to the collector tank were replaced. A new Rotax 582 engine was installed on November 10, 2006. METEOROLOGICAL INFORMATION The 1153 recorded weather at Destin-Fort Walton Beach Airport (DTS), Destin, Florida, 6 miles south of the accident site, included variable winds at 4 knots, visibility 10 miles, clear skies, temperature 31 degrees Celsius (C), dew point 22 degrees C, and an altimeter setting of 30.04 inches of mercury. AIRPORT INFORMATION The airport was privately owned and operated, with a single north-south turf runway. The runway was 3,300-feet-long and 75-feet-wide. WRECKAGE AND IMPACT INFORMATION The FAA inspector, who responded to the accident site, reported that the airplane impacted the runway and runway edge lights. The airplane had been landing to the south and that it came to rest next to a tree line. The wings were folded aft along the fuselage. The outboard tip of the left wing exhibited impact and crush damage. The leading edge was bent aft from approximately the spanwise midpoint to the wingtip, and the trailing edge was extensively damaged. The right wing exhibited minor damage. The engine remained attached to airplane. One of the two propeller blades remained attached to the hub. The separated blade exhibited spanwise fractures, and the attached blade exhibited damage to the tip and spanwise fractures to the trailing edge. Control continuity was verified for all control surfaces. A local aircraft mechanic, under the supervision of the FAA inspector, checked continuity of the engine and reported that it rotated smoothly through the crankcase up to the pistons. Compression on all cylinders was achieved using the thumb compression method. The magnetic plug was removed, and it was free of metal particulates. The mechanic also verified that fuel was present in the fuel tank located in the wing on the airplane. The airframe and flight control system components revealed no evidence of preimpact mechanical malfunction. The wreckage was transported to a secure salvage facility, and was stored outside, where it was partially exposed to the elements. It was examined on September 26, 2008 by a National Transportation Safety Board investigator. The reduction gearbox M8 Allen screw that was replaced prior to the accident flight was found secure. The fuel screen was clean, throttle control continuity was confirmed, and full throttle control movement was verified. No preimpact mechanical malfunctions were observed.