COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Fokker F27 Series Aeroplanes AD/F27/140 Fuselage Skin Lap Joints Below the Cabin Floor 6/95 Applicability: All F27 aircraft S/N 10102 to 10375 in pre Service Bulletin (SB) F27/53-68 or pre SB F27/53-85 configuration that have been operated at a nominal pressure differential of 5.5 psi. Requirement: 1. Modify the fuselage skin lap joints below floor level from FS 1400 to FS 12975 as applicable, in accordance with Fokker SB F27/53-116, paragraph 2, Parts 1 and 2. 2. Modify the fuselage skin lap joints below floor level from FS 12975 to FS 16669, in accordance with Fokker SB F27/53-116, paragraph 2, Part 3. Note: Netherlands RLD AD 94-092(A) refers. Compliance: 1. Modify in accordance with Requirement 1 before 32 000 flights or before 1 July 1996, whichever occurs later. 2. Modify in accordance with Requirement 2 before 56 000 flights or before 1 July 1996, whichever occurs later. Note 1: The formulae in SB F27/53-116 may be used to calculate a higher threshold for aircraft which initially operated at 5.5 psi but which have been subsequently modified to operate at 4.16 psi. Note 2: Modification in accordance with this AD cancels the inspection requirement of SIP items 53-30-02, 53-30-03 and 53-30-04. Background: Recent fatigue analysis has indicated that certain configuration fuselage lap joints below the floor are susceptible to multi-site cracking when the aircraft has been operated at a pressure differential of 5.5 psi. As the area is difficult to inspect a modification is required to improve the fatigue life.