COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Fokker F27 Series Aeroplanes AD/F27/138 Wing Lower Skin at Stringers 4 to 7 2/95 Applicability: All F27 aircraft (except Mk 050). Requirement: 1. Perform an X-ray inspection of the wing lower surface stringers 4 to 7 at Wing Stations (WS) 11260, 11860, 12660, and 13460. Inspect in accordance with Fokker Service Bulletin (SB) F27/57-70 paragraph 2 part 2. 2. Modify the wing lower surface rib to stringer connections where stringers 4 to 7 join to the ribs at WS 11260, 11860, 12660, and 13460. Modify in accordance with Fokker SB F27/57-70 paragraph 2 part 1. Note: RLD AD 93-094(A) refers. Compliance: 1. Inspect in accordance with Requirement 1 before 30000 flights or within 2000 flights after 2 February 1995 whichever is the later. Re-inspect at intervals not to exceed 4000 flights until modified in accordance with Requirement 2. 2. Modify in accordance with Requirement 2 before 30000 flights or before 31 July 1996 whichever occurs later. Background: When incorporating SB F27/57-68 (cracking of wing upper surface stringers) some operators discovered cracking in the lower surface stringers. Inspection and modification are required to resolve the problem.