COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES DHC-3 (Otter) Series Aeroplanes AD/DHC-3/34 Amdt 1 Tailplane Main Rib Forward Flange and Forward Lower Flange 10/99 Applicability: All Model DHC-3 aircraft. Requirement: Action in accordance with Bombardier Regional Aircraft Service Bulletin (SB) 3/46 Revision E. Compliance: Unless accomplished in the 12 months prior to 7 October 1999, before 7 October 2000; thereafter at intervals not to exceed 2 calendar years, until Modification 3/935 (SB 3/50) is incorporated. This Amendment becomes effective on 7 October 1999. Background: The manufacturer received reports of the tailplane centre section main rib cracking at the main rib forward and forward lower flange radii. Such cracking could lead to failure of the rib structure supporting the tailplane front attachment fitting. Amendment 1 is issued to introduce a modification which constitutes terminating action to the repetitive inspection requirements of this Directive. The original issue of this Airworthiness Directive became effective on 17 May 1990.