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/F100/5 Powerplant - Lower Cowl Door Engagement 1/99 Applicability: Fokker F28-100 and F28-70 series aircraft, serial numbers 11244 through 11469, 11471, 11474 through 11483, 11489, 11490, 11491, 11494, 11498, 11499, 11501, 11502, 11504, 11506, 11507, 11512 through 11515, 11517, 11520, 11528, and 11537. Requirement: 1. Modify the hook and latch assembly of the lower cowl doors in accordance with the instructions in Part 1 of the Accomplishment Instructions of Fokker Service Bulletin SB F100-71-019 dated 21 March 1996. Note: The accomplishment of Part 1 of Fokker SB F100-71-003, dated 14 April 1989, or Revision 1 dated 08 August 1989, or Revision 2 dated 21 November 1994 is considered an acceptable means of compliance for this requirement. 2. Inspect both engine's lower cowling door hook and latch assemblies in accordance with Part 2 of the Accomplishment Instructions of Fokker SB F100-71-019 dated 21 March 1996. 3. Modify the lower cowl door's mid clevis fitting in accordance with the Accomplishment Instructions of Fokker SB P41230-71-07 dated 15 February 1996. Note: RLD Airworthiness Directive 1989-049/3 (A) dated 28 June 1996 refers. Compliance: 1. Unless already accomplished, on a limited number of aircraft as applicable, within 2500 flight cycles of the last inspection performed in accordance with BLA 89- 049/2. 2. Within 2500 flight cycles since new or since last inspection in accordance with BLA 89-049/2 as applicable. 3. Following the discovery of a cowl mismatch during accomplishment of Requirement 2. above. This Airworthiness Directive becomes effective on 28 January 1999. Background: Experience has shown that an aerodynamic gap/mismatch may exist between the fixed engine cowl and the lower cowl door. Should this mismatch exceed a certain value, one or more hooks may not engage properly. This degrades the redundancy of the lower cowl door engagement in the closed position and could lead to an unsafe condition. This Directive introduces a one time inspection and corrective action if necessary, to measure the gap/mismatch on applicable aircraft. This Directive also introduces a modification to the hook and latch assembly on a limited number of the applicable aircraft.