COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Ayres Thrush (Snow) Commander Series Aeroplanes AD/AC-SNOW/23 Vertical Fin Rear Spar 10/95 Applicability: All aircraft with model and serial number listed in Ayres Corporation Service Bulletin SB-AG-38. Requirement: Visually inspect the vertical fin rear spar for cracks at the upper, centre and lower rudder hinge bearing mounts. Compliance: Initially inspect before 100 hours' time in service after 14 September 1995. Re-inspect at intervals not to exceed 100 hours. Modification in accordance with Ayres Corporation Service Bulletin SB-AG-38 or a scheme accepted by the Authority cancels the Requirement of this Directive. Background: When installing the modification of Ayres Corporation Service Bulletin SB-AG-38 on one aircraft the vertical fin rear spar was found to be cracked in several locations. The cracks may be aggravated by internal corrosion of the bearings restricting free movement.