{"id":"F2006B10116","name":"AD/G21/2 - Horizontal Stabiliser Lower Strut Fittings - Inspection and Life Limitation","slug":"ad-g21-2-horizontal-stabiliser-lower-strut-fittings-inspection-and-life-limitation","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":55646,"registerId":"commonwealth-F2006B10116-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/G21/2 - Horizontal Stabiliser Lower Strut Fittings - Inspection and Life Limitation","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)  Grumman G21 (Goose) Series Aeroplanes\n\n \n\n# AD/G21/2  Horizontal Stabiliser Lower Strut Fittings - Inspection and Life Limitation\n\nApplicability: All model G21A.\n\n# 10/77\n\n \n\nRequirement: 1 Inspect the threaded portion of the strut lower adjustable end fitting P/N 12561-3 for cracks using a magnetic particle inspection technique.\n\n \n\n2. Retire from service strut lower adjustable end fittings P/N 12561-3.\n\n \n\nNote: Grumman Customer Bulletin G21A No. 3 and FAA AD 53-31-2 refer.\n\n \n\nCompliance: 1. Initially, before issue of Certificate of Airworthiness and thereafter at intervals not exceeding 1000 hours time in service.\n\n \n\n2. Before exceeding 3200 hours time in service.\n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The AD text itself imposes inspection and retirement requirements for part P/N 12561-3 on all G21A aeroplanes (Applicability; Requirement 1–2; Compliance 1–2). The instrument does not state that it expands or narrows scope relative to an earlier instrument; it simply prescribes the specific inspections and a life limit. No change of scope from an earlier intent is indicated in the provided text."},"complexity_factors":["Narrow applicability (only Grumman G21A models) reduces scope complexity (Applicability).","Two clear mandatory actions (inspect using magnetic particle technique; retire part P/N 12561-3) keep substantive requirements limited (Requirement 1–2).","Specified inspection interval (initial before Certificate of Airworthiness; then every 1,000 hours) and fixed life limit (3,200 hours) require service-hour tracking and scheduling (Compliance 1–2).","Technical specificity (magnetic particle inspection) requires access to particular non-destructive testing capability and qualified personnel (Requirement 1).","References to external documents (Grumman Customer Bulletin and FAA AD) may require cross-checking for procedural detail not contained in the AD itself (Note).","No alternative compliance paths, acceptance criteria, or record-keeping details are provided in the AD text, which concentrates complexity in operational implementation rather than legal interpretation."],"plain_english_summary":"### What this directive does\n\nThis Airworthiness Directive (AD) applies to all Grumman G21A (Goose) aeroplanes (Applicability). It requires two specific actions for the horizontal stabiliser lower strut adjustable end fitting, part number 12561-3:\n\n- Inspect the threaded portion of that fitting for cracks using a magnetic particle inspection technique (Requirement 1). The first inspection must be done before the aircraft is issued its Certificate of Airworthiness and then repeated at intervals not exceeding 1,000 hours time in service (Compliance 1).\n\n- Remove (retire from service) any fitting P/N 12561-3 before it reaches 3,200 hours time in service (Requirement 2; Compliance 2).\n\nThe AD cites Grumman Customer Bulletin G21A No. 3 and FAA AD 53-31-2 as related references (Note).\n\n### Who is affected and who decides\n\n- Affected parties: owners and operators of all Grumman G21A aircraft, because the AD is applicable to that model (Applicability).\n- Decision-maker: the Civil Aviation Safety Authority (CASA) issued this AD under the Schedule of Airworthiness Directives (header information).\n\n### Who pays and what changes in behaviour\n\n- Who pays: operators/owners bear the costs of performing the magnetic particle inspections and of replacing/retiring fittings before 3,200 hours (Requirement 1–2; Compliance 1–2). The AD does not specify funding or reimbursement.\n- Behaviour changes required: operators must ensure inspections are scheduled and recorded before initial Certificate of Airworthiness and at no greater than 1,000-hour intervals, and must remove the specified fittings before they exceed 3,200 hours time in service (Requirement 1–2; Compliance 1–2).\n\n### Implementation effects, compliance burden and practical points\n\n- Inspection method: the rule specifies a magnetic particle inspection technique, so compliance requires access to that NDT method and qualified personnel or service providers (Requirement 1).\n- Timing and operational impact: the initial inspection timing (before Certificate of Airworthiness) and recurring 1,000-hour interval create fixed inspection windows operators must meet; retiring fittings at 3,200 hours imposes an absolute life limit that will require tracking hours-on-part and part replacement planning (Compliance 1–2).\n- References and traceability: the AD points to a manufacturer bulletin and a FAA AD for related technical context; operators may consult those documents for additional procedural detail but the AD itself prescribes the inspections and life limit (Note).\n\n### Trade-offs, risks and limits (mechanically stated)\n\n- Cost vs. component life: the AD forces earlier removal of any P/N 12561-3 fitting at or before 3,200 hours, which creates a predictable replacement cost and potential aircraft downtime (Compliance 2). The text does not quantify costs.\n- Technical compliance requirement: specifying magnetic particle inspection focuses compliance on one NDT technique; the AD does not provide alternative inspection methods or acceptance criteria beyond the technique named (Requirement 1).\n- Enforcement and discretion: the AD sets fixed intervals and a life limit; it does not include discretion for alternative compliance schemes or exemptions within the text provided.\n\nSource citations: Applicability; Requirement 1–2; Compliance 1–2; Note."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a vintage Airworthiness Directive from 1977 (indicated by \"10/77\" in the reference) that has remained focused on its original narrow purpose: addressing a specific structural fatigue issue in a particular aircraft part. The scope has not expanded beyond the original safety concern."},"complexity_factors":["Very short document (approximately 150 words)","Only 2 substantive requirements with clear compliance deadlines","Single defined part number (P/N 12561-3)","No cross-references to other legislation sections (only references to related manufacturer bulletins)","Simple conditional logic: inspect every 1,000 hours, retire at 3,200 hours","No nested exceptions or conditional exemptions"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for a specific type of aircraft.\n\n**What it does:**\nThis directive applies to all **Grumman G21A \"Goose\"** seaplanes (a vintage amphibious aircraft from the 1930s-40s). It requires owners/operators to:\n\n- **Inspect** a specific metal fitting (part number 12561-3) that connects the horizontal tail stabiliser to the fuselage, using a magnetic particle inspection technique to detect cracks\n- **Permanently retire** (replace) these fittings before they reach 3,200 hours of flight time\n\n**Who it affects:**\nAnyone who owns, operates, or maintains a Grumman G21A aircraft in Australia.\n\n**Why it matters:**\nThe horizontal stabiliser keeps the aircraft level in flight. If the strut fitting fails due to metal fatigue or cracking, the pilot could lose control of the aircraft. This AD prevents catastrophic failure by catching cracks early and forcing replacement of parts before they reach a dangerous age."}},"importantCases":[],"_links":{"self":"/api/acts/ad-g21-2-horizontal-stabiliser-lower-strut-fittings-inspection-and-life-limitation","history":"/api/acts/ad-g21-2-horizontal-stabiliser-lower-strut-fittings-inspection-and-life-limitation/history","analysis":"/api/acts/ad-g21-2-horizontal-stabiliser-lower-strut-fittings-inspection-and-life-limitation/analysis","conflicts":"/api/acts/ad-g21-2-horizontal-stabiliser-lower-strut-fittings-inspection-and-life-limitation/conflicts","importantCases":"/api/acts/ad-g21-2-horizontal-stabiliser-lower-strut-fittings-inspection-and-life-limitation/important-cases","documents":"/api/acts/ad-g21-2-horizontal-stabiliser-lower-strut-fittings-inspection-and-life-limitation/documents"}}