AIRWORTHINESS DIRECTIVE For the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CAR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section. Fokker F100 (F28 Mk 100) Series Aeroplanes AD/F100/51 Vertical Stabiliser Torsion Box - 2 7/2002 Applicability: Model F.28 Mk.0100 aircraft, serial numbers 11244 through 11460, 11463 through 11469, 11471, 11474 through 11483, 11489, 11490, 11491, 11497, 11498, 11499, 11501, 11502, 11504, 11506, 11507, 11512 through 11515, 11517, and 11520. Requirement: Cold expand the 12 hi- lok bolt holes at the Rib 5.0 position of the vertical stabiliser torsion box, in accordance with Parts 1, 2, and 3 of the Accomplishment Instructions, as applicable, of Fokker Service Bulletin (SB) F100-55-023, dated 3 January 1995. Note: Netherlands CAA AD 1995-017 refers. Compliance: 1. For aircraft which have already been in-service modified to post SB F100-55- 018-configuration: Before accumulating 10,000 flight cycles since the accomplishment of the modification in accordance with Fokker SB F100-55-018 (as required by AD 93- 069); or, 2. For aircraft which are still in pre-SB F100-55-018-configuration: Concurrent with the accomplishment of the modification in accordance with Fokker SB F100-55-018 (as required by AD 93-069); or, 3. For aircraft which have had SB F100-55-018 factory incorporated: Before accumulating 10,000 flight cycles since new. This Airworthiness Directive becomes effective on 11 July 2002. Fokker F100 (F28 Mk 100) Series Aeroplanes AD/F100/51 (continued) Background: Netherlands Airworthiness Directive 93-069 (AD/F100/17) was issued to prevent cracks in the vertical stabiliser torsion box, and requires the accomplishment of Fokker SB F100-55-018, which introduces support brackets on Rib 5.0. More recent full-scale fatigue tests, however, have revealed cracks in Rib 5.0, due to this modification. This condition, if not corrected, produces a too rapid change in structural strength and may lead to consequential cracking of the vertical stabiliser struc ture. This Directive requires an additional modification that introduces cold- expanded bolt holes in the torsion box at Rib 5.0 of the vertical stabiliser. David Alan Villiers Delegate of the Civil Aviation Safety Authority 31 May 2002 The above AD is notified in the Commonwealth of Australia Gazette on 19 June 2002.