COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Beechcraft 56TC (Turbo Baron) Series Aeroplanes AD/BEECH 56/22 Amdt 2 Wing Main Spar Centre Section 11/90 Applicability: Model 56TC and A56TC, Serial Number TG-1 to TG-94 inclusive. Requirement: Inspect the wing forward spar carry through structure forward and aft frames, in accordance with Beechcraft Service Bulletin No 2269 Rev 1, dated March 1990. Note: FAA AD 90-08-14, Amendment 39-6563 refers. Compliance: Within 100 hours' time in service after 1 November 1990, or prior to the accumulation of 1500 hours total time in service, whichever occurs later. Where no cracks are found, repeat the inspections at intervals not to exceed 500 hours' time in service. Where cracks are found, repeat the inspections at intervals as detailed in the Requirement Document. Crack limits must not be exceeded. Specific locations repaired or reinforced by the installation of the applicable Beech P/N 58-4008 kit, or other approved scheme, need not be inspected before 1500 hours' time in service after installation of that kit, however affected areas adjacent to repair doublers remain subject to the above compliance. Aircraft inspected in accordance with the previous issue of this Directive shall be considered to have been inspected in accordance with this amendment. Background: There have been numerous reports of cracking at various locations in the wing carry though structure. This problem was first found in Australia in 1981. The cracking is caused by fatigue in the corners of the fuselage frame webs, around and between huckbolts and in areas where stringers are attached. To date there have been no reports of cracks having progressed to failure, however uncorrected this condition could lead to eventual catastrophic failure. Engineering analysis has determined, however, that cracking within defined limits is not an immediate threat to safe flight, if assessed and monitored in accordance with this amendment. Compliance threshold has been adjusted to align it with manufacturers recommendations.