COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Pratt and Whitney Canada Turbine Engines - PT6T Series AD/PT6T/7 Gas Generator Case Seam Weld 2/88 DM Applicability: PT6T-3, -3B, -6 engines not incorporating gas generator case stiffening plates fitted in accordance with PT6T-3, -3B Overhaul Manual P/N 3017843, Section 72-30-30 or, PT6T-6 Overhaul Manual P/N 3024843, Section 72-31-30 or, during manufacture. Requirement: 1. Inspect gas generator case for possible seam weld cracking in accordance with PWC ASB No A-5239 paragraph 2A, items 1 to 7. 2. Modify both gas generator case longitudinal (butt) welds in accordance with PWC ASB No A-5239 paragraph 2B, items 1 to 16. Reference Documents: Bell ASB 412-87-30 Bell ASB 212-87-45 PWC SIL 5031 PWC SIL 5031 Rev 1 Compliance: 1. (a) All gas generator cases with more than 1200 hours TSN - No later than 31 December 1987, and thereafter at intervals not to exceed 600 hours. (b) All gas generator cases with less than 1200 hours TSN - Prior to 1200 hours TSN or 31 December 1987, whichever occurs later, and thereafter at intervals not to exceed 600 hours. 2. At next power section repair or overhaul. Background: The manufacturer advises of eleven reported occurrences of gas generator case seam weld cracking. One occurrence resulted in a gas generator case rupture.