COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Airtractor AT-300, 400 and 500 Series Aeroplanes AD/AT/13 Wing Spar Cap Corrosion 7/92 Applicability: Models AT-300, AT-301, & AT-302 with S/N's 300-0001 through 301-0688; Model AT-400 with S/N's 400-0244 through400-0415; & Model AT-400A all S/N's. Requirement: Action in accordance with Air Tractor Inc. Service Letter No. 90. Note: FAA AD 92-07-14 Amdt 39-8210 refers. Compliance: Prior to 30 September 1992; and thereafter at intervals not to exceed 12 calendar months. Background: The FAA has received three reports of badly corroded wing spar caps on the affected aircraft. The actions specified by this Directive are intended to prevent failure of the wing structure.