On March 8, 2003, about 1130 eastern standard time, a Brantly B-2B helicopter, N2238U, was substantially damaged while hovering at the Zelienople Municipal Airport (8G7), Zelienople, Pennsylvania. The sole occupant, a non-rated pilot was not injured. Visual meteorological conditions prevailed and no flight plan had been filed for the personal flight that was conducted under 14 CFR Part 91. The helicopter was owned by the pilot. The pilot had been practicing landings at a private farm, and then flew to 8G7 to refuel. While hovering over a taxiway, the tail rotor assembly separated and the helicopter began to spin. The helicopter struck the ground and rolled over. Examination of the helicopter was performed by a Federal Aviation Administration (FAA) inspector. The separated tail rotor assembly and gearbox was found to have the mounting portion of the top bulkhead ring still attached by the associated attachment bolts. The top bulkhead ring had separated completely from it's attachment flanges at the bulkhead flange transition radius. Examination of the helicopter tail boom pylon revealed the top bulkhead ring attachment flange remained riveted in place. Chaffing damage was observed on the left and right side fracture surfaces, consistent with preexisting cracks. In addition, areas of corrosion were observed on the inner surface of the top bulkhead ring. The FAA inspector noted that the top bulkhead ring was manufactured with a 1.5-inch diameter "lightening-hole" forward of the tail rotor gearbox attachment point, and approximately centered on its horizontal face. According to a representative of the manufacturer, one reason for the hole was to facilitate access for visual inspection of the interior portions of the vertical section of the tail boom pylon. In addition, utilizing an inspection mirror, the underside and flanges of the top ring bulkhead and the tail rotor gearbox attachment bolts could be inspected. The pilot stated he maintained the helicopter. He did not posses an FAA airframe or powerplant certificate. According to maintenance records, the helicopter's most recent annual inspection was performed on November 2, 2001. The pilot reported that the helicopter had been operated for about 55 hours since the inspection. The pilot did not posses a pilot or medical certificate. He reported 60 hours of total flight experience, all accumulated in the accident helicopter.