AIRWORTHINESS DIRECTIVE For the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/HILLER 12/34 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. Hiller UH-12 Series Helicopters AD/HILLER 12/34 Amdt 1 Main Transmission Oil Filter 4/2002 Applicability: All UH-12 series helicopters, including Soloy Conversions, incorporating a main transmission part number (P/N) 23500-3, 237700-3, -5, -7, -9, -21 and –23. Requirement: Inspect the main transmission oil filter and if applicable, the magnetic particle chip detector, in accordance with Hiller Aviation Service Bulletin UH-12-23-2. Note: FAA Airworthiness Directive 81-17-03 refers. Compliance: 1. Main transmissions not incorporating Rogerson Hiller Corporation Service Bulletin UH-12-23-3: Unless previously accomplished; within 25 hours' time in service after this Directive is effective and thereafter at intervals not to exceed: 1. Piston engine helicopters: 55 hours. b. Turbine engine helicopters: 27.5 hours. 2. Main transmissions incorporating Rogerson Hiller Corporation Service Bulletin UH-12-23-3: Unless previously accomplished, within 25 hours' time in service after this Directive is effective and thereafter at intervals not to exceed: 1. Piston engine helicopters: 110 hours. b. Turbine engine helicopters: 55 hours. This Amendment becomes effective on 18 April 2002. Hiller UH-12 Series Helicopters AD/HILLER 12/34 Amdt 1 (continued) Background: This Directive was originally issued to require monitoring of the main transmission oil filter. The requirement was in response to reports of extensive wear in the planetary assemblies. This amendment introduces extended compliance intervals for helicopters incorporating a modified main transmission and provides an extended compliance to assist maintenance scheduling.. Eugene Paul Holzapfel Delegate of the Civil Aviation Safety Authority 10 March 2002