COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES DHC-6 (Twin Otter) Series Aeroplanes AD/DHC-6/69 Amdt 1 Corrosion Prevention and Control 13/99 Applicability: All Model DHC-6 aircraft. Requirement: To maintain corrosion to Level 1 or better, accomplish the following: 1. Develop a schedule for accomplishing the Corrosion Tasks in accordance with Requirement 2 of this Directive. 2. In accordance with the following schedule, accomplish all Corrosion Tasks specified in Part 3 of the de Havilland DHC-6 Twin Otter Corrosion Prevention and Control Manual, PSM 1-6-5, Revision 1, dated 16 December 1998 (hereafter referred to as "the Manual"), by performing the seven basic tasks defined at paragraph 3.0 of the Manual. The final deadline and rate of initial complete aircraft inspections are specified in the following table: Applicable Aircraft Serial Numbers Accomplishment Deadline for All Aircraft in Applicable S/N Range Minimum Rate of Initial Inspections of Aircraft in Applicable S/N Range 001 to 199 31 December 1995 All aircraft 200 to 439 31 December 1996 50% or one (1) aircraft per calendar year, whichever is greater 440 to 659 31 December 1998 25% or one (1) aircraft per calendar year, whichever is greater 660 to 819 31 December 1999 20% or one (1) aircraft per calendar year, whichever is greater 820 to 844 31 December 2002 Commencing 1 January 1999, 25% or one (1) aircraft per calendar year, whichever is greater Once the first CT commences, the aircraft is not to be returned to service until all CTs, excluding the float inspections, have been completed and any resulting rework and parts replacement have been completed. Floats that were on an aircraft just prior to the aircraft being inspected in accordance with the Manual do not have to be inspected simultaneously with that same aircraft; however, the aircraft cannot be returned to service with floats that have not had their applicable CTs completed and any resulting rework and parts replacement completed. COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES When performing CTs with less than a five year Repeat Interval (R) after the initial inspection of the aircraft, all CTs with the same R interval are to be completed during one maintenance visit and any resulting rework and parts replacement must be performed before returning the aircraft or floats to service. Corrosion is to be addressed in accordance with the references specified in paragraph 4.0 of Part 3 of the Manual. Corrosion level determinations are to be based on the definitions contained in Part 1 of the Manual. Corrosion classified as Level 1 need not be reported. Level 2 corrosion may be consolidated with a quarterly report of corrective action, and submitted to the Authority District (Airport) Office under cover of a single MDR. Level 3 corrosion shall be reported by MDR. Note: Transport Canada AD CF-94-12R1 refers. Compliance: 1. Prior to 31 January 1995. 2. Commencing 1 February 1995. The compliance of the original issue of this Directive remains unchanged. This Amendment becomes effective on 30 December 1999. Background: As aircraft become older, they are more likely to exhibit indications of corrosion. Transport Canada Aviation, in conjunction with other airworthiness authorities, has committed itself to ensuring that additional maintenance programs for older aircraft are developed and implemented to minimise and control corrosive deterioration that could jeopardise airworthiness. Amendment 1 is issued in response to revision of the related Transport Canada AD which introduces Revision 1 of the CPC Manual which deletes the requirement for repetitive inspections after initial compliance. Transport Canada AD CF-99-11 (AD/DHC-6/72) now provides for the requirement to perform the inspections a second time, but on a more flexible schedule than required by the original issue of this Directive. The original issue of this Directive became effective on 8 December 1994.