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-6/72 Corrosion Prevention and Control - 2 13/99 Applicability: Model DHC-6 aircraft that are in full compliance with Airworthiness Directives AD/DHC-6/69 (CF-94-12) or AD/DHC-6/69 Amdt 1 (CF-99-12R1). Requirement: Action in accordance with the technical requirements of Transport Canada (TC) AD CF-99-11. The following is a substitution for the last paragraph of the Requirement document which states reporting requirements: 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. Compliance: As specified in the Requirement document with a revised effective date of 30 December 1999. This Airworthiness Directive becomes effective on 30 December 1999. Background: The Corrosion Prevention and Control Manual requirement for repetitive inspections after initial compliance was deleted by the issue of AD/DHC-6/69 Amdt 1. This Directive is issued in response to a new TC AD which requires Corrosion Tasks (CTs) to be performed on a repetitive basis and provides the option of performing the CTs during several maintenance visits in one year (Part A) or a specific group of CTs on an annual basis over a five year period (Part B).