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/F100/17 Vertical Stabiliser Torsion Box 4/99 Applicability: F.28 Mk.0100 aircraft, serial numbers 11244 through 11419, and 11421. Requirement: 1. Modify the Vertical stabiliser Torsion Box in accordance with Fokker SB F100- 55-009 dated 9 April 1990; and modify the Vertical Stabiliser Torsion Box in accordance with Fokker Service Bulletin (SB) F100-55-014 dated 29 November 1990, unless Fokker SB F100-55- 018 dated 19 May 1993 was carried out prior to accumulation of 6,000 flight cycles. Note 1: The modification in accordance with Fokker SB F100-55-014 dated 29 November 1990 is not required if the modification in Fokker SB F100-55-018 dated 19 May 1993 is accomplished before the aircraft accumulates 6,000 flight cycles since new. Note 2: Some aircraft had the above modifications included before delivery or as a result of compliance with other Airworthiness Directives. 2. Inspect the flanges and finger strips at Rib 5.0 of the vertical stabiliser in accordance with Fokker SB F100-55-019 Revision 1 dated 19 May 1993. 3. Modify Rib 5.0 of the vertical stabiliser in accordance with Fokker SB F100-55- 018 dated 19 May 1993. Note 3: If during any inspection as required by this AD, cracks are found, contact the manufacturer for repair instructions. Note 4: RLD BLA 93-069(A) refers. Compliance: 1. Prior to accumulating 6,000 flight cycles or within 30 days, whichever occurs last. 2. Prior to accumulating 8,500 flight cycles since new or within 30 days, whichever occurs last. Thereafter reinspect every 2000 flight cycles, until modified in accordance with Requirement 3. 3. Prior to accumulating 7,300 flight cycles since new or Prior to accumulating 13,500 flight cycles since new and immediately after an inspection in accordance with Requirement 2 of this AD. Note 5: If the modifications in Requirement 3 are completed prior to 7,300 flight cycles, then the requirement to inspect immediately prior to the installation of those modifications is not required. COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES This Airworthiness Directive becomes effective on 22 April 1999. Background: During full-scale fatigue tests, cracks were found at bolt holes in the RH flange of the torsion box and in the finger strip on the LH flange at Rib 5.0 of the vertical stabiliser. If not corrected, these cracks may lead to a deteriorated fatigue life of the vertical stabiliser structure.