On March 24, 1999, at 1300 central standard time, an Extra Flugzeugbau GMBH 300S, N9K, operated by Above & Beyond Aviation, Inc., Creve Couer, Missouri, experienced a failure of the upper left longeron and a diagonal cross member at the horizontal stabilizer attach point. The failure occurred when the airline transport rated pilot entered a roll maneuver while practicing for an airshow. The pilot was able to land the airplane without further incident. The accident occurred in Dow, Illinois. The pilot was not injured and the airplane was substantially damaged. The local 14 CFR Part 91 flight was operating in visual meteorological conditions without a flight plan. The pilot stated during a telephone interview that he departed the Creve Couer Airport and flew out to their "practice box" at the Koenig Airstrip in Dow, Illinois. He stated that during the flight he heard a "tapping" noise when he slowed the airplane for landing. After landing it was determined that the noise was from a loose cosmetic seal on the landing gear. The seal was removed and he departed to practice his airshow routine. He stated that after departing, he performed a one-half roll to check the tightness of his seat belt and to check for loose objects in the cockpit. He then called his safety monitor and reported that he was "inbound for the box." He reported he made a left turn and descended toward the "box." Upon entering the "box" he initiated a left roll and approximately 90 degrees into the roll he heard a "bang." He stated he leveled the airplane and asked the ground crew if they saw anything come off of the airplane. The ground crew reported that they did not see anything come off. The pilot then landed the airplane uneventfully. Inspection of the airplane by maintenance personnel revealed the upper left longeron and a diagonal cross member in the empennage had failed. The failed components were shipped to the NTSB Materials Laboratory for a metallurgical examination. The inspection revealed the fracture on the upper left longeron intersected the fillet weld at the base and most forward end of the forward stabilizer attach bracket. Examination of the longeron failure revealed characteristics typical of a fatigue crack. The forward diagonal brace running forward of the horizontal stabilizer fractured approximately 1 inch below and slightly forward of the attachment assembly for the horizontal stabilizer. Examination revealed that a fatigue crack had propagated through approximately 90% of the tube circumference. (See attached Materials Laboratory Factual Report) Additional Information On May 3, 1995, Extra Flugzeugbau issued Service Bulletin No. 300-2-95, Revision "A" effective for models EA-300, EA-300S, and EA-300L. This service bulletin stated the upper longeron located forward of the attachment fitting for the horizontal stabilizer needed to be inspected for cracking. The service bulletin called for an immediate visual inspection and recurring inspections every 50 hours. The service bulletin states that in case of doubt use a dye penetrant for the inspection. The operator of N9K discovered a crack in the upper left longeron near the horizontal stabilizer attach fitting during an annual inspection in December, 1997. Total time on the N9K was 856.3 hours. The operator contacted Extra and was provided instructions to repair the crack and to install a gusset to strengthen the longeron at the horizontal stabilizer attach fitting. On February 4, 1998, Extra issued Service Bulletin No. 300-2-95 Revision "B." Part I of this service bulletin calls for the same inspection as in Revision "A". Part II of this service bulletin called for the same repair that the operator had already performed on N9K after having found the cracks. Revision "B" states, "No further inspection has to be performed after being compliant with Part II of this service bulletin." On July 15, 1998, Extra issued Service Bulletin No. 300-2-95, Revision "C". This service bulletin is differs from Revision "B" in that the gusset had been redesigned. In Revision "C" the shape of the gusset is different, the gusset is larger, and there are four holes for rosette welds instead of three. The operator of N9K contacted Extra and was informed that if they had complied with Revision "B", they were also in compliance with Revision "C." The operator stated that even though it was not required per the service bulletin, they continued to inspect this area and no further cracking was noted.