AIRWORTHINESS DIRECTIVE For the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/AT/17 Amdt 2 and issues the following AD under subregulation 39.1 (1) of CAR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section. Airtractor AT 300, 400 and 500 Series Aeroplanes AD/AT/17 Amdt 3 Vertical Fin Front and Rear Spars 3/2003 Applicability: All Airtractor models AT-300, 400 and 500 series which do not incorporate the fin front spar attachment fitting steel reinforcement plate in accordance with Snow Engineering Service Letter SL #138, SL#155 and SL #196, as applicable. AT301 model S/Ns 301-0100 to 301-0736 must comply with SL#196. Requirement: 1. Inspect the vertical fin front spar attachment fitting as detailed in Snow Engineering Service Letters SL #138, SL#155 and SL #196, as applicable. 2. For aircraft listed in the Models and Serial Numbers section of SL#138, SL #155 or SL#196, modify by installing the fin front spar steel reinforcement plate in accordance with SL#138, SL #155 or SL#196, respectively. Note 1: FAA ADs 97-14-05, 2000-11-05 and NPRM No. 2000-CE-59-AD refer. Note 2: FAA AD 2000-11-05 added additional serial numbers to the applicability of SL# 196. Compliance: For Requirement 1: 1. If SL #138 is applicable, then unless already accomplished, initially inspect within the next 25 hours time in service, thereafter, re-inspect at intervals not exceeding 25 hours time in service. b. If SL#155 is applicable, then unless already accomplished, initially inspect prior to exceeding 2000 hours time in service, or within 25 hours time in service after 20 March 2003, whichever occurs later. Thereafter, re-inspect at intervals not exceeding 100 hours time in service. c. If SL#196 is applicable, then unless already accomplished, initially inspect prior to exceeding 4000 hours time in service, or within 25 hours time in service after 20 March 2003, whichever occurs later. Thereafter, re-inspect at intervals not exceeding 100 hours time in service. For requirement 2: Before further flight following the discovery of cracking. This Amendment becomes effective on 20 March 2003. Airtractor AT 300, 400 and 500 Series Aeroplanes AD/AT/17 Amdt 3 (Continued) Background: The initial issue of this AD was the result of in-flight incidents in the USA resulting in partial separation of the fin from the aircraft. Investigations found that the 3/16 inch thick aluminium alloy front spar attachment plate had failed through fatigue. Snow Engineering SL #138 introduced a recurring inspection and a terminating modification (steel attachment plate) which was mandated by the AD. Subsequently, an incident occurred where a 1/4 inch aluminium attachment fitting failed in identical circumstances. Amendment 1 expanded the applicability of the AD to all aircraft. The terminating modification of SL #138 was applicable to a limited range of models and serial numbers only. Snow Engineering has now issued SL #196 which expands the aircraft serial number applicability for the inspections and terminating modification. The FAA has issued AD 2000-11-05 which requires inspection of unmodified aircraft at 100 hour intervals rather than 25 hours as previously. Amendment 3 expands the applicability to all the aircraft models listed in Snow Engineering SL #155 which were not covered by the other SL's. The FAA has issued NPRM No. 2000-CE-59-AD to cover the serial numbers listed in SL#155 which are not covered by the other SLs and FAA ADs. Amendment 2 of this Airworthiness Directive became effective on 7 September 2000. Amendment 1 of this Airworthiness Directive became effective on 2 October 1996. The original issue of this Airworthiness Directive became effective on 11 December 1995. David Alan Villiers Delegate of the Civil Aviation Safety Authority 7 February 2003 The above AD is notified in the Commonwealth of Australia Gazette on 26 February 2003.