COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Piper PA-38 (Tomahawk) Series Aeroplanes AD/PA-38/23 Upper Forward and Aft Vertical Fin Spar - Inspection and Reinforcement Applicability: All model PA-38-112 with S/Nos. 38-78A0001 to 38-82A0122. Document: Piper Service Bulletin No. 763. 9/83 Compliance: On vertical fins which have achieved 500 hours time in service, within 25 hours time in service and thereafter at intervals not exceeding 100 hours time in service until Kit 764-965 is installed. Background: Field reports indicate that cracks have occurred in the area where the horizontal stabiliser attachment brackets attach to the upper end of the vertical fin forward and aft spars.