On March 17, 2004, about 0720 Pacific standard time, an experimental Wallace Skybolt, N41BB, experienced an in-flight breakup while executing an aerobatic maneuver near Reno/Stead Airport (4SD), Reno, Nevada. The owner/pilot was operating the airplane under the provisions of 14 CFR Part 91. The private pilot, the sole occupant, sustained serious injuries; the airplane was destroyed. The personal local flight departed Stead about 0645. Visual meteorological conditions prevailed, and no flight plan had been filed. The primary wreckage was at 39 degrees 41.34 minutes north latitude and 119 degrees 57.43 minutes west longitude. The Federal Aviation Administration (FAA) accident coordinator responded to the accident scene. He interviewed the pilot on March 25, 2004. The pilot reported that he was executing an aerobatic outside loop maneuver. During the bottom of the loop, while inverted, his airspeed was about 160 mph, and he was about 8,000 feet mean sea level (msl). While pushing forward on the stick to about -2.5G to start the ascending part of the maneuver, the airplane began to vibrate violently. The pilot felt the vibration in the airframe, not in the stick or the rudder. He felt the vibration for 1 to 2 seconds, followed by the left wing of the airplane detaching from the airplane's structure. During the airplane's continued disintegration, the pilot was able to release his seat belt and exit the airplane. The pilot deployed his parachute, which opened just prior to his impacting the ground. The airplane received its original experimental certification in January 1975. Subsequently, the airplane received annual condition inspections. In January 1979, at 307 hours total time, the airplane was disassembled, inspected/repaired, and reassembled/recovered. In March 2000, a larger engine/prop combination was installed. In January 2001, at 733 hours total time, the airframe only was disassembled, inspected, and repaired as necessary, and reassembled/recovered. The wings were not disassembled, inspected, repaired or recovered. According to the accident airplane's records and the pilot's statement, it had been more than 20 years since the wings had undergone any extensive inspection, repair, or rebuild with the fabric removed.