COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Piper PA-31 Series Aeroplanes AD/PA-31/47 Elevator Balance Weight - Modification 7/76 Applicability: All model PA-31-325 C/R with S/Nos. 31-7400990, 31-7512006 to 31-7512058; all model PA-31-350 with S/Nos. 31-5001 to 31-7552108. Document: Piper SB No. 500. Compliance: Within 100 hours time in service after 30 July 1976.