What was found
ON BOTH THE LH AND RH SIDES OF THE FUSELAGE, THE U-BOLT ATTACHMENT TUBE, PN 2-1949, IS CRACKED AT THE AFT ATTACHMENT BOLT FOR THE MLG. THE CRACKS WERE DISCOVERED DURING AN ANNUAL INSPECTION STARTED ON 08/01/2018. THE ISSUE WAS ALSO DISCOVERED IN ANOTHER ACFT OF SIMILAR DESIGN THAT WE ALSO MAINTAIN. N555XD, A 8KCAB, SN 1135-2013, ON 07/15/2018 DURING A PREFLIGHT INSPECTION. THAT ACFT IS CURRENTLY ENROUTE TO AMERICAN CHAMPION AIRCRAFT FOR A REPAIR AT THE FACTORY. THE PROBABLE CAUSE OF THE DEFECTS IN BOTH AIRPLANES CAN BE ATTRIBUTED TO LANDING CYCLES CAUSING FATIGUE IN THE STRUCTURAL MEMBER. HARD LANDINGS COULD ALSO BE A CONTRIBUTING FACTOR, AS N555XD ONLY HAD 1110.6 HOURS TOTAL TIME. THE BEST RECOMMENDATION TO PREVENT REOCCURRENCE WOULD BE A RE-DESIGN OF THE AREA IN QUESTION. EITHER THE INSTALLATION OF A STIFFER AROUND THE MEMBER OR REMOVAL OF REPLACEMENT OF THE MEMBER WITH A STRONGER COMPONENT SHOULD BE ADVISED. UNTIL SUCH TIME AS A FIX IS ENGINEERED, I WOULD SUGGEST THE ISSUANCE OF AN AIRWORTHINESS DIRECTIVE REQUIRING INSPECTION EVERY 100 HOURS OF OPERATION, WITH TERMINATION OF THE AD CONTINGENT ON INSTALLATION OF THE STIFFENER OR REPLACEMENT MEMBER. I WOULD ALSO RESTRICT AEROBATIC FLIGHT UNTIL A FIX IS ISSUED AS THE CRACKS ARE VERY CLOSE TO THE WING STRUT ATTACHMENT POINTS.