COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Bombardier (Boeing Canada/De Havilland) DHC-8 Series Aeroplanes AD/DHC-8/64 Wing Fuel Tanks - Access Panel Sealing 10/99 Applicability: All DHC-8 aircraft, all Models, serial numbers 3 through 543. Requirements: Change Wing Tank Access Panel Seals, using ModSum 8Q1000797, in accordance with the provisions of Bombardier Service Bulletin 8-57-41, dated 9 February 1999. Note: Transport Canada Airworthiness Directive CF-99-20 dated 20 July 1999 refers. Compliance: Prior to 9 February 2000 unless previously accomplished. This Airworthiness Directive becomes effective on 7 October 1999. Background: During routine maintenance a sealing problem has been discovered with the upper wing tank access panels. An O-ring larger than specified had been fitted to the access panel during production with the result that the access panel fit was incorrect. This poor fit could lead to eventual loss of lightning protection for the fuel tanks through fretting and corrosion of the wing ladder plate and displacement of the adjacent channel seal.