{"id":"F2006B10206","name":"AD/GAF-N22/58 Amdt 5 - Horizontal Stabiliser","slug":"ad-gaf-n22-58-amdt-5-horizontal-stabiliser","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":55864,"registerId":"commonwealth-F2006B10206-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/GAF-N22/58 Amdt 5 - Horizontal Stabiliser","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-generator: Aspose.Words for .NET 22.10.0\n---\n\n?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"no\"?>\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  GAF N22 and N24 Series Aeroplanes\n\n \n\n# AD/GAF-N22/58\n\nAmdt 5\n\nApplicability: All models.\n\n# Horizontal Stabiliser 8/96\n\n \n\nRequirement: 1. Remove modification N568 machined braces, P/N 1/N-30-250, and inspect the horizontal stabiliser centre section structure, in accordance with ASTA Nomad Service Bulletin ANMD-55-26, Revision 8, Accomplishment Instructions, Part 1.\n\n \n\n2.    Reinforce the dorsal fin & the rear fuselage structure, in accordance with ASTA Nomad SB ANMD-55-26, Revision 8, Accomplishment Instructions, Part 2.\n\n \n\n3.    Rework the horizontal stabiliser structure and install modification N663 and N768, in accordance with ASTA Nomad Service Bulletin ANMD-55-26, Revision 8, Accomplishment Instructions, Part 3 or 4 as applicable.\n\n \n\nNote: For the purposes of this AD, installation of modifications N663 and N768 does not 'zero time' the tailplane.\n\n \n\n4.    Retire the complete horizontal stabiliser structure from service, including trim tab assemblies.\n\n \n\nCompliance: Accomplish Requirements 1, 2 and 3 before further flight, unless previously accomplished, except that changes introduced by Revision 8 of SB ANMD-55-26, including new lockwire requirements, may be accomplished not later than the next issue of a Maintenance Release after 18 July 1996.\n\n \n\nFor tailplanes with the original main spars, or that were resparred at less than 5000 hours tailplane time in service, retire the horizontal stabiliser from service before exceeding 15000 hours spar time in service; or\n\n \n\nFor tailplanes resparred after 5000 hours tailplane time in service, retire the horizontal stabiliser from service before 20,000 hours tailplane time in service.\n\n \n\nNote: For the purposes of this AD, \"resparred\" means a complete main spar 'tip to tip' and centre section box replacement.\n\n \n\nBackground: This directive arose from field reports of cracking in the stabiliser centre section.\n\nInvestigation of a fatal tailplane failure suggested that undetected cracks may propagate beyond safe limits, despite relatively stringent inspections. Reports have also been received of cracks occurring in the spar cap flanges fitted with modification N569. This modification impedes inspection of the area and is required to be removed.\n\n \n\nAmendment 2 was issued to require compliance with SB Revision 2, which called up repetitive eddy current inspections, since it was found that visual inspection was not sufficiently sensitive in the web lightening hole area.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\nAmendment 3 introduced Revision 3 of the SB, which required precautionary measures to be taken during engine ground running to minimise loads on the horizontal stabiliser, and a modification which would constitute terminating action for the repetitive inspections.\n\n \n\nAmendment 4 introduced Revision 4 of the SB, which changed the effectivity to include post-mod N663 aircraft. Investigation by the manufacturer suggested that stresses in the centre section may eventually cause cracking even in aircraft modified to N663. This Revision also altered engine ground run conditions, and initial inspection and accomplishment instructions.\n\n \n\nAmendment 5 introduces a retirement life, and calls up Revision 8 which specifies N768 as the required terminating modification. The manufacturer's substantiation of the tailplane fatigue life is ongoing. Testing and analysis undertaken to date are not completely exhaustive in determining the final life. However, based on the information provided to the Authority, an interim life has been established. This life will be reviewed as the manufacturer's test program progresses.\n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":6,"scope_assessment":{"changed":true,"description":"Yes. The AD’s scope has expanded since its initial issuance. The original directive and early amendments emphasised inspection sensitivity (introducing eddy-current inspections) and removal of inspection-obscuring fittings. Subsequent amendments added operational precautions (engine ground-run limits) and a terminating modification option (N663). This Amendment 5 further changed scope by mandating a specific terminating modification (N768 called up by SB Revision 8) and by introducing interim compulsory retirement life limits for the complete horizontal stabiliser. Those additions move the instrument from primarily inspection-and-mitigation measures toward structural modification and lifecycle management (mandatory replacement at stated hours), increasing the regulatory intrusion on aircraft maintenance planning and long-term operating cost compared with the original inspection-focused intent."},"complexity_factors":["Multiple cross-references to an external document (ASTA Nomad Service Bulletin ANMD-55-26 Revision 8) with Parts 1–4 that define detailed technical work","Conditional compliance timings (immediate before further flight for most items; a narrow deferral for some Revision 8 changes to the next Maintenance Release after 18 July 1996)","Two-tiered retirement life rules depending on whether/when the tailplane was resparred (< or > 5,000 hours), plus distinct use of the terms “tailplane time in service” and “spar time in service” (potential for confusion)","Several discrete modification identifiers to remove or install (N568 removal, N569 referenced in background, installation of N663 and N768)","Interplay of recurring inspection regime (earlier amendments) and a later terminating modification plus an interim mandatory life limit (adds conditional logic and future amendment risk)","Defined technical term included in the AD (“resparred” defined as complete main spar tip-to-tip and centre section box replacement)","Urgent compliance element (\"before further flight\") increases operational complexity for scheduling and parts availability"],"plain_english_summary":"**What this instrument does (mechanically)**\n\n- Applies to all GAF Nomad N22 and N24 series aeroplanes.\n- Requires removal of a previously fitted brace modification (N568, P/N 1/N-30-250) and an inspection of the horizontal stabiliser centre section following ASTA Nomad Service Bulletin ANMD-55-26 Revision 8, Part 1.\n- Requires reinforcement of the dorsal fin and rear fuselage per ANMD-55-26 Revision 8, Part 2.\n- Requires reworking the horizontal stabiliser and installing modifications N663 and N768 per ANMD-55-26 Revision 8, Part 3 or 4 as applicable. (The AD explicitly states installing N663/N768 does not \"zero time\"—it does not reset the tailplane’s service life.)\n- Requires retirement (permanent removal from service) of the complete horizontal stabiliser structure, including trim tab assemblies, under specified life limits:\n  - If the tailplane has original main spars, or was resparred when it had under 5,000 hours tailplane time in service: retire the stabiliser before exceeding 15,000 hours spar time in service.\n  - If the tailplane was resparred after accumulating more than 5,000 hours tailplane time in service: retire the stabiliser before 20,000 hours tailplane time in service.\n  - The AD defines “resparred” to mean a complete main spar replacement (tip-to-tip and centre section box).\n\n- Compliance timing: Requirements to remove N568, inspect, reinforce and install N663/N768 must be accomplished before further flight unless already done. A limited exception allows some changes introduced by SB Revision 8 (for example new lockwire rules) to be completed by the next Maintenance Release after 18 July 1996.\n\n**Who this affects**\n\n- Aircraft owners and operators of GAF Nomad N22/N24 series aeroplanes.\n- Maintenance organisations and licensed engineers who must carry out the inspections, eddy-current testing, structural reinforcements and modification installations in accordance with the manufacturer's Service Bulletin.\n- Parts suppliers and overhaul facilities that supply or manufacture spar assemblies, N663/N768 modification kits, and replacement stabiliser structures.\n\n**Why it matters (stated purpose and operational effect)**\n\n- The AD responds to field reports of cracking in the stabiliser centre section and at least one fatal failure attributed to undetected tailplane cracking. It states that visual inspection alone proved insufficient and that earlier modifications (including N569/N568) either obscured inspection access or did not eliminate the cracking risk.\n- The AD’s stated safety mechanism is to remove impediments to inspection, require more sensitive inspections (eddy current where called up in the SB), strengthen adjacent structure, mandate terminating modifications (N663 and N768), and impose a life limit on the stabiliser to prevent fatigue-related failure beyond an interim safe-life estimate.\n\n**Practical consequences, implementation and incentives**\n\n- Who pays: aircraft owners/operators bear the direct costs — removal work, nondestructive testing (eddy current capability), reinforcement and modification installation, and eventual replacement of retired stabilisers.\n- Operational impact: some work must be done before further flight, creating immediate downtime risk; other incremental changes may be deferred to the next scheduled Maintenance Release only where expressly allowed (lockwire change exception).\n- Maintenance burden: requires specific SB work (Revision 8), nondestructive testing capability or contracted specialist services, and accurate tracking of tailplane/spar hours to enforce retirement limits.\n- Supply and logistics risk: enforcement of a retirement life will increase demand for replacement stabilisers or complete spar work; availability of parts or approved repair/overhaul services could affect aircraft availability and costs.\n- Effect on commercial choices: operators must budget for recurring replacement of stabilisers at the mandated hours and may change utilization patterns (reduce hours on type, transfer aircraft, or retire airframes) to manage costs.\n- Certainty and discretion: the AD prescribes specific SB actions and life limits; the manufacturer’s ongoing fatigue testing is acknowledged and the AD’s life limits are described as interim, so changes can follow as testing results arrive. That ongoing testing introduces some regulatory uncertainty (future amendment risk).\n\n**Trade-offs and risks explicitly raised by the text**\n\n- Benefit concentrated on safety of aircraft occupants and public by reducing risk of undetected fatigue cracking in the tailplane.\n- Cost is concentrated on the relatively small group of Nomad operators and maintenance suppliers (inspection, modification and replacement costs; aircraft downtime). Costs are diffuse to no other party under the AD.\n- Opportunity cost: resources devoted to these modifications and replacements are not available for other maintenance or upgrades.\n- Implementation risk: constrained supply of replacement stabilisers or approved modification kits, and the need for specialist inspection techniques (eddy current) may lengthen downtime or increase outsourcing.\n- The AD recognises the manufacturer’s life substantiation is ongoing and treats the retirement life as interim, creating a risk that operators may have to undertake further changes if testing revises the life shorter or longer.\n\n**Source claims vs observable mechanisms**\n\n- The AD claims visual inspection is insufficient (supported by earlier revisions calling up eddy-current inspections). Mechanistically, this changes the inspection technology required and thus the skills and equipment operators must use or procure.\n- The AD claims certain earlier modifications impede inspections; it responds by mandating their removal (N568 removal) and requiring a replacement structural solution (N663/N768). The mechanism: remove an inspection-obstructing part and install approved modifications intended to eliminate the root cause or provide a terminating fix.\n\n(References in text: Requirements 1–4 and the Compliance paragraph, and the Background and Amendment history describing why the measures were added.)"},"kimi_summary":{"content_quality":"ok","complexity_score":6,"scope_assessment":{"changed":true,"description":"The directive has expanded significantly from its original scope. Initially focused on inspection and removal of problematic braces (Modification N568), it has grown through five amendments to include: repetitive eddy current inspections (Amendment 2), engine ground-running restrictions (Amendment 3), expanded effectivity to post-modification aircraft (Amendment 4), and finally a mandatory retirement life for the entire horizontal stabiliser structure (Amendment 5). The original 'inspect and repair' approach evolved into a 'life-limited component' regime with hard retirement deadlines, reflecting the manufacturer's ongoing inability to fully substantiate unlimited fatigue life."},"complexity_factors":["Multiple amendment history (Amendments 2-5) embedded in background text, creating layered conditional requirements","Technical aviation terminology requiring specialist knowledge (e.g., 'resparred', 'zero time', 'eddy current inspections', 'web lightening hole')","Dual compliance pathways based on maintenance history (original spars vs. resparred at <5000 hours vs. resparred after 5000 hours)","Cross-references to external documents (ASTA Nomad Service Bulletin ANMD-55-26, Revision 8) with multiple parts (1-4) that are incorporated by reference","Conditional deadlines: 'before further flight' vs. 'next Maintenance Release after 18 July 1996'","Specific part numbers and modification numbers (N568, N569, N663, N768) that must be tracked against aircraft records","Nested definitions: 'resparred' is specially defined for this AD, and 'zero time' is explicitly negated for certain modifications"],"plain_english_summary":"This CASA Airworthiness Directive requires operators of GAF N22/N24 Nomad aircraft to inspect and modify the tail structure and to retire horizontal stabilisers after specified flight hours (15,000 or 20,000 depending on spar replacement). It responds to fatal accidents and field reports of undetectable cracking that can lead to catastrophic tail failure. Non‑compliance grounds affected aircraft until actions are completed."},"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"}},"importantCases":[],"_links":{"self":"/api/acts/ad-gaf-n22-58-amdt-5-horizontal-stabiliser","history":"/api/acts/ad-gaf-n22-58-amdt-5-horizontal-stabiliser/history","analysis":"/api/acts/ad-gaf-n22-58-amdt-5-horizontal-stabiliser/analysis","conflicts":"/api/acts/ad-gaf-n22-58-amdt-5-horizontal-stabiliser/conflicts","importantCases":"/api/acts/ad-gaf-n22-58-amdt-5-horizontal-stabiliser/important-cases","documents":"/api/acts/ad-gaf-n22-58-amdt-5-horizontal-stabiliser/documents"}}