COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Fokker F100 (F28 Mk 100) Series Aeroplanes AD/F100/10 Engine Mount Shear Shelf Web 4/99 Applicability: F.28 Mk.0100 aircraft, serial numbers, 11244 through 11308, 11310, 11312 through 11314, 11316, 11321, 11328 and 11329. Requirement: 1. Inspect the engine mount shear shelf webs around the areas of the fixed cowl aft hook centreline and the fixed cowl mid hook centreline for cracks and damage, and reinforce the engine mount shear shelf webs in accordance with the Accomplishment Instructions Part 1 or Part 2, as applicable, of Fokker Service Bulletin (SB) F100-71-012 dated 7 February 1992. 2. Repair cracks in accordance with Fokker F.28 Mk.0100 Structural Repair Manual (SRM). Note: RLD BLA 92-032 refers. Compliance: 1. Unless previously accomplished, before accumulating 12,000 flight hours since new. 2. If cracks are found during the inspection in accordance with Requirement 1, repair before further flight. This Airworthiness Directive becomes effective on 22 April 1999. Background: Interference has been found to be possible between the fixed cowl mid and aft hooks and the engine mount shear shelf web. Aside from a noticeable increase in vibration and noise, this interference can cause cracks and other damage to the shear shelf web. This in turn affects fatigue life. This AD requires the affected areas to be inspected and subsequently reinforced.