Incident Description
A pilot reported hearing a 'bang' while initiating a left roll at the beginning of an airshow routine practice flight. The pilot subsequently landed the airplane without further incident. An inspection conducted after the landing revealed that the upper left longeron and a diagonal cross member in the empennage had failed.
Findings
Metallurgical examination of the failed components determined that they had failed due to fatigue. The aircraft manufacturer, Extra, had issued three Service Bulletins (300-2-95, Revisions 'A', 'B', and 'C') concerning cracks in this area.
Service Bulletin History
Revision 'A' of the bulletin called for inspections of the area. In 1997, cracks were found on aircraft N9K, and repairs were made in accordance with Extra's instructions. Revision 'B' was subsequently issued, requiring the same repairs that the operator had already made if cracks were found. When Revision 'C' was issued, it called for the same type of repair, but the gusset to be used was shaped differently and was larger. The operator was informed by Extra that if they were in compliance with Revision 'B', they were also considered to be in compliance with Revision 'C'.