COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Fokker F50 (F27 Mk 50) Series Aeroplanes AD/F50/78 Amdt 1 Outer Wing Stringer-to-Rib Connections 3/99 Applicability: Model F.27 Mk.050 and 0502 aircraft with serial numbers 20103 through 20298. Requirement: Inspect and modify in accordance with RLD AD 1998-023/2. Note: Fokker Service Bulletin F50-57-019 refers. Compliance: At the inspection threshold and modification times specified in the Requirement Document. This Amendment becomes effective on 25 March 1999. Background: On early Model F.27 Mk.050 series aircraft, loose connections between ribs and stringers may still occur as in the case of the Model F.27 series aircraft, which was addressed by AD/F27/139. Such deficient connections reduce the static buckling strength of the wing skin, and may cause fretting of the stringer. This condition, if not corrected, could result in fatigue cracking of the stringer and skin. This Directive requires inspection and modification of the connections between stringers and ribs outboard of Wing STA.10760. Amendment 1 is issued in response to a revision of the RLD AD which introduces a repeat inspection requirement until the required modification is accomplished. The original issue of this Airworthiness Directive became effective on 21 May 1998.