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-31/50 Horizontal Stabiliser Stringer Attachment - Inspection 11/76 Applicability: All model PA-31 and PA-31-325 with S/Nos. 31-7612060 to 31-7612080, 31- 7612082 to 31-7612089, 31-7612091, 31-7612096 and 31-7612099. All model PA- 31-350 with S/Nos. 31-7652105 to 31-7652115, 31-7652117, 31-7652118, 31- 7652120 to 31-7652146, 31-7652148 to 31-7652162, 31-7652164, 31-7652165 and 31-7652168. Document: Piper SB No. 521. Compliance: Within 100 hours time in service after 30 November 1976.