COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES GAF N22 and N24 Series Aeroplanes AD/GAF-N22/28 Amdt 4 Horizontal Stabiliser and Trim Tab System 7/93 Applicability: All N22 and N24 Series. Requirement: Unless already accomplished: 1. Modify in accordance with GAF SB NMD-55-12 (Mod. N439). 2. Inspect in accordance with GAF SB NMD-55-5 Revision 4. Compliance: 1. Forthwith. 2. Prior to the next inspection for maintenance release issue after 30 November 1986, and thereafter at intervals not exceeding 110 hours time in service. The Compliance of this Directive remains unchanged. This Amendment is effective from 24 June 1993. Background: An inflight incident occurred which involved extreme vibration in the empennage area and the loss of 150mm of the outboard section of the horizontal stabiliser trim tab. Amendment 3 reflected the latest revision of SB NMD-55-5, and incorporated the intent of AD/GAF-N22/38 which had been cancelled. Amendment 4 is issued in response to Revision 4 of the Requirement 2 Document which changes the Applicability to include all models.