{"id":"F2006B10175","name":"AD/GAF-N22/28 Amdt 4 - Horizontal Stabiliser and Trim Tab System","slug":"ad-gaf-n22-28-amdt-4-horizontal-stabiliser-and-trim-tab-system","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":55819,"registerId":"commonwealth-F2006B10175-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/GAF-N22/28 Amdt 4 - Horizontal Stabiliser and Trim Tab System","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nGAF N22 and N24 Series Aeroplanes\n\nAD/GAF-N22/28\n\nAmdt 4\n\n  \nHorizontal Stabiliser and Trim Tab System 7/93\n\nApplicability: All N22 and N24 Series. Requirement: Unless already accomplished:\n\n    Modify in accordance with GAF SB NMD-55-12 (Mod. N439).\n\n    2. Inspect in accordance with GAF SB NMD-55-5 Revision 4\\. Compliance: 1. Forthwith.\n\n2. Prior to the next inspection for maintenance release issue after 30 November 1986, and thereafter at intervals not exceeding 110 hours time in service.\n\nThe Compliance of this Directive remains unchanged. This Amendment is effective from 24 June 1993.\n\nBackground: 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.\n\nAmendment 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.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":true,"description":"Originally this directive may have applied to specific models only. Amendment 4 explicitly expands applicability to 'all models' of the N22 and N24 series, broadening the safety net after the manufacturer revised their service bulletin."},"complexity_factors":["Very short document (under 300 words)","Only 2 substantive requirements (modification + inspection)","No defined terms section — relies on external manufacturer documents (Service Bulletins)","Simple conditional structure: 'Unless already accomplished' is the only qualifier","Minimal cross-referencing (only to specific Service Bulletin numbers)","Clear compliance deadlines with straightforward intervals"],"plain_english_summary":"This mandatory CASA Airworthiness Directive requires owners/operators of GAF N22 and N24 aeroplanes to correct a known structural weakness by installing Mod. N439 (per Service Bulletin NMD‑55‑12) and to carry out recurring inspections of the horizontal stabiliser and trim‑tab system (per Service Bulletin NMD‑55‑5 Rev.4). \n\nIt follows an incident where severe vibration led to loss of a trim tab; compliance prevents similar control failures and is required for legal flight in Australia."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"Amendment 4 expands applicability to include all N22 and N24 models by adopting Revision 4 of SB NMD-55-5, thereby increasing the set of aircraft required to comply (Background: 'changes the Applicability to include all models')."},"complexity_factors":["Cross-references to two external service bulletins (GAF SB NMD-55-12 Mod. N439 and GAF SB NMD-55-5 Rev 4) — requires operators/maintainers to obtain and follow those documents (Requirement 1 and 2).","Timing linkage: immediate compliance for the modification if not already done, and inspection timing tied to the next maintenance‑release after 30 Nov 1986 and then every 110 hours TIS — creates record‑keeping and scheduling obligations (Compliance: paragraphs 1 and 2).","Applicability broadened to 'all N22 and N24 Series' by Amendment 4 — expands the population of affected aircraft and increases overall compliance workload (Background: Amendment 4 description).","Technical work required (modification of stabiliser/trim tab system) necessitates certified maintenance organisation/appropriately rated personnel and parts, imposing direct costs on operators (Requirement 1).","The AD does not reproduce technical steps; implementers must interpret and apply the service bulletins, creating reliance on bulletin clarity and supplier availability (Requirement references only).","Low regulatory ambiguity otherwise: the AD specifies what to do, who it affects, and inspection intervals, keeping legal interpretation demands modest."],"plain_english_summary":"This airworthiness directive requires owners/operators of GAF N22 and N24 series aeroplanes to carry out a specific modification (per GAF SB NMD-55-12, Mod. N439) and to inspect the horizontal stabiliser and trim tab system per GAF SB NMD-55-5 Revision 4. It responds to an in‑flight incident where part of the trim tab was lost. Compliance requires immediate modification if not done, and recurring inspections tied to maintenance releases and a 110‑hour interval, with costs and work falling to aircraft operators and their maintenance organisations."}},"importantCases":[],"_links":{"self":"/api/acts/ad-gaf-n22-28-amdt-4-horizontal-stabiliser-and-trim-tab-system","history":"/api/acts/ad-gaf-n22-28-amdt-4-horizontal-stabiliser-and-trim-tab-system/history","analysis":"/api/acts/ad-gaf-n22-28-amdt-4-horizontal-stabiliser-and-trim-tab-system/analysis","conflicts":"/api/acts/ad-gaf-n22-28-amdt-4-horizontal-stabiliser-and-trim-tab-system/conflicts","importantCases":"/api/acts/ad-gaf-n22-28-amdt-4-horizontal-stabiliser-and-trim-tab-system/important-cases","documents":"/api/acts/ad-gaf-n22-28-amdt-4-horizontal-stabiliser-and-trim-tab-system/documents"}}