AIRWORTHINESS DIRECTIVE On the effective date specified below, and for the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/DHC-1/22 Amdt 3 and issues the following AD under subregulation 39.001(1) of CASR 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. De Havilland DHC-1 (Chipmunk) Series Aeroplanes AD/DHC-1/22 Amdt 4 Tailplane Structure 13/2011 Applicability: All English production (C1) all models and Portuguese production (T Mk 20) aircraft which have not been modified in accordance with a scheme approved by the authority (locally developed reinforcement kit). Requirement: Inspect the tailplane upper and lower spar flanges in accordance with British Aerospace TNS CT(C1) No. 157, Issue 3, dated 28 May 1986. Note: TNS No. 138 Issue 5 is the subject of UK CAA AD 2804 PRE 80 and CASA AD/DHC-1/12 Amendment 6. Compliance: From the date of compliance with the initial inspection, repeat the inspections of paragraph 8 of the TNS at intervals not exceeding 6 years, unless the aircraft is operated on a Role Factor of 4 (see TNS CT(C1) No. 138 Issue 5), in which case the inspection interval shall not exceed 3 years. This Amendment becomes effective on 22 June 2011. Background: This directive requires repetitive radiographic inspection of the tailplane upper and lower spar flanges at the fuselage attachment brackets. Some aircraft have been modified to incorporate a locally developed reinforcement kit, so as to be excluded from this AD. This amendment adds the Portuguese manufactured T Mk 20 to the applicability of this Airworthiness Directive. A review indicates that this inspection is also applicable to this model. Amendment history: Amendment 1, effective 30 November 1985, introduced a radiographic inspection of the tailplane front spar joints. It also required a repeat of the inspections carried out in accordance with the initial issue of this AD. Amendment 2, effective 13 July 2000, excluded modified aircraft from the requirement. Amendment 3, effective 23 October 2008, required repetitive radiographic inspections of the upper and lower spar flanges at the fuselage attachment brackets. Some aircraft have been modified to incorporate a locally developed reinforcement kit. The opportunity was also taken to update the TNS reference. No additional work was required as a result of this amendment. Glen Steemson Delegate of the Civil Aviation Safety Authority 16 June 2011