{"id":"F2006B11284","name":"AD/ML-M4/15 Amdt 4 - Retirement Life of Fatigue Critical Components","slug":"ad-ml-m4-15-amdt-4-retirement-life-of-fatigue-critical-components","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":57097,"registerId":"commonwealth-F2006B11284-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/ML-M4/15 Amdt 4 - Retirement Life of Fatigue Critical Components","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)  \nMaule M-4 Series Aeroplanes\n\nAD/ML-M4/15\n\nAmdt 4\n\n  \nRetirement Life of Fatigue Critical Components 12/88 DM\n\nApplicability: All Models.\n\nRequriement: 1. Remove wing lift strut forks and inspect for cracking using a magnetic particle technique in accordance with ANO 108.8.\n\n    2. Retire wing lift strut forks from service.\n\n    3. Install placards reading NO STEP in letters at least 25 mm high on the left and right wing struts, either by painting or by the use of durable adhesive labels, in a colour contrasting to the strut colour, the lettering to commence approximately 150 mm from the bottom of the struts and be oriented so that it can be read when looking in a forward direction with respect to the aeroplane. For those aircraft which have a fairing over the front and rear strut lower ends a single placard on the fairing will suffice, otherwise both struts must be placarded.\n\nNote: The standard M4 series forks have a 7/16 inch threaded shank diameter. Some aircraft have been retrofitted with M5 series struts which have forks with a 1/2 inch threaded shank. The M5 type forks are exempt from the requirements of this Directive, however it is recommended that the “NO STEP” placards be retained for consistency and as an additional safeguard against accidental damage.\n\nCompliance: For Para 1 - Prior to achieving 200 hours component time in service or three years after initial installation whichever occurs first, and thereafter at intervals not exceeding 500 hours component time in service. For aircraft which have exceeded these limits, perform the initial inspection within 100 hours time in service after 30 November 1986.\n\nFor Para 2 - Retire wing lift strut forks prior to the accumulation of 1000 hours component time in service or within 200 hours time in service after 30 November 1986, whichever occurs later.\n\nFor Para 3 \\- Within 100 hours time in service after 30 November 1986.\n\nBackground: Service experience with forks on other aircraft types indicates the possibility of fatigue failure. The heavier M5 type forks are exempt from the requirements. This Amendment deletes the life limitation previously placed on the wing, on the basis of data received from the manufacturer which shows that wing fatigue failure is unlikely within the economic life of the airframe.","sortOrder":0}],"analysis":{"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":true,"description":"This amendment narrowed the scope compared to earlier versions. The original directive apparently imposed retirement limits on the entire wing structure, but Amendment 4 removed that requirement after the manufacturer provided data showing wing fatigue failure was unlikely. The scope was reduced to focus only on the strut forks, which remain the critical fatigue concern."},"complexity_factors":["Short, single-purpose directive (approximately 300 words)","Only 3 substantive requirements with clear, numbered paragraphs","Simple conditional logic: one exemption for M5 series forks","Compliance deadlines use basic arithmetic (hours of service or calendar dates)","Minimal defined terms (only 'component time in service' requires implicit understanding)","No cross-references to other legislation beyond 'ANO 108.8' (a maintenance standard)","Single amendment note explaining the change from previous version"],"plain_english_summary":"This CASA Airworthiness Directive targets Maule M‑4 series aeroplanes to prevent wing‑failure from fatigue cracks in wing lift strut forks. It mandates periodic magnetic particle inspections, retirement of forks at 1,000 hours or by a deadline, and fitting \"NO STEP\" placards. It affects owners, operators and maintenance engineers. M‑5 upgraded forks (thicker threads) are exempt from inspections/retirement; Amendment 4 removes a prior whole‑wing retirement requirement based on new manufacturer data."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"This amendment narrowed and retargeted the Directive compared with the prior version. The Background states that the Amendment deletes a previous life limitation on the wing (a broad structural life cap) based on manufacturer data that wing fatigue failure is unlikely. Instead of a wing life limit, the current text imposes component‑level measures: inspection and retirement of the wing lift strut forks and placarding of the struts. In short, the scope moved from a whole‑wing life limitation to focused controls on a specific fatigue‑critical component (the forks), with an exemption for heavier M5 forks; this represents a substantive change in regulatory scope and the locus of intervention."},"complexity_factors":["Three discrete operative requirements (Para 1–3) with cross‑references to compliance timings","Conditional timing rules using 'whichever occurs first/whichever occurs later' for inspections and retirement","A specific exemption for M5‑type forks (note) that alters applicability","Reference to an external technical standard for inspection technique (ANO 108.8)","Legacy compliance deadlines tied to a calendar date (30 November 1986) that create staggered initial compliance windows"],"plain_english_summary":"**What this instrument does (mechanically)**\n\n- Requires owners/operators of Maule M‑4 series aeroplanes to remove the wing lift strut forks and inspect them for cracking using a magnetic particle technique (see Paragraph 1).\n- Requires the retirement (permanent removal from service) of the wing lift strut forks on a hours‑based life limit (see Paragraph 2).\n- Requires installation of “NO STEP” placards on the left and right wing struts (or a single placard on a strut fairing where fitted) to reduce the risk of accidental damage from stepping on the strut (see Paragraph 3).\n- Exempts forks fitted to M5‑type struts (1/2 inch threaded shank) from the inspection and retirement requirements; the placard requirement is still recommended for consistency (see Note).\n\n**Who this affects**\n\n- Owners and operators of Maule M‑4 series aircraft that retain the original M4‑type wing lift strut forks (7/16 inch shank).\n- Maintenance organisations and certificated maintenance personnel who must perform the magnetic‑particle inspections and carry out component retirement.\n- Parts suppliers and repair shops that supply replacement forks or retrofit M5 struts — demand may shift toward the M5 type because it is exempt from the life‑limit requirement.\n\n**Why it matters (stated purpose and practical implications)**\n\n- Stated purpose: service experience on similar aircraft shows the possibility of fatigue failure of fork components; the Directive aims to reduce the risk of in‑flight structural failure by inspecting and retiring potentially fatigue‑susceptible forks and by discouraging stepping on the strut (Background; Paras 1–3).\n\n- Practical implications and trade‑offs:\n  - Safety mechanism: periodic non‑destructive inspection (magnetic particle) and a defined retirement life for the fork component (Para 1 and Para 2) directly target component fatigue risk.\n  - Compliance cost: the owner/operator pays for removal, inspection, replacement forks, labour and aircraft downtime. Those costs are concentrated on Maule M‑4 operators and maintenance providers; they are diffuse across the broader aviation sector.\n  - Behavioural response and substitution: because M5 forks (heavier, 1/2\" shank) are exempt, operators may choose retrofits to avoid recurring inspections and retirement limits. That substitution changes demand for parts, may increase up‑front retrofit cost, and can shift long‑term maintenance expenses.\n  - Operational impact: required placards (Para 3) are a low‑cost precaution to reduce accidental loading; they impose minimal economic burden but change cockpit/airframe marking practice.\n  - Implementation risk: accurate compliance depends on correct identification of fork type (M4 vs M5), competent magnetic particle inspections (ANO 108.8 referenced), and recordkeeping of component service hours. Misidentification or poor inspection quality could leave residual risk.\n  - Regulatory discretion and certainty: the Directive sets specific hours and calendar limits (see Compliance) and an explicit exemption for one retrofit type (Note), which reduces ambiguity about who must comply.\n\n**Key compliance timings (mechanical rules)**\n\n- Inspection (Para 1): initial magnetic‑particle inspection before the fork reaches 200 hours component time or three years after installation, whichever comes first; thereafter every 500 hours component time. If forks already exceeded those limits, do the initial inspection within 100 hours after 30 Nov 1986.\n- Retirement (Para 2): remove the fork from service before it accumulates 1000 hours component time, or within 200 hours after 30 Nov 1986, whichever is later.\n- Placards (Para 3): fit the NO STEP placards within 100 hours time in service after 30 Nov 1986.\n\n**Who pays and who decides**\n\n- Owners/operators pay for inspections, replacements and placarding. Maintenance providers perform inspections and issue the maintenance records required by aviation regulation (inspection technique is mandated by ANO 108.8).\n- The Civil Aviation Safety Authority enforces the Directive; maintenance personnel must follow the specified inspection method and retirement schedule.\n\n**Concise statement of effects on markets and choices**\n\n- Increases recurring maintenance cost and recordkeeping for aircraft retaining M4‑type forks (concentrated cost on those owners).\n- Creates a substitution incentive toward M5‑type forks/retrofits because they are exempt from the inspection/retirement mandate; that may raise demand for retrofit parts and maintenance work for such conversions.\n- Lowers the risk of fatigue‑related fork failure (the stated safety benefit) at the expense of component replacement and inspection costs.\n\n**Relevant references in the Directive**: Paragraph 1 (inspection), Paragraph 2 (retirement), Paragraph 3 (placards), Note (M5 exemption), Compliance schedule, Background (removal of prior wing life limit)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-ml-m4-15-amdt-4-retirement-life-of-fatigue-critical-components","history":"/api/acts/ad-ml-m4-15-amdt-4-retirement-life-of-fatigue-critical-components/history","analysis":"/api/acts/ad-ml-m4-15-amdt-4-retirement-life-of-fatigue-critical-components/analysis","conflicts":"/api/acts/ad-ml-m4-15-amdt-4-retirement-life-of-fatigue-critical-components/conflicts","importantCases":"/api/acts/ad-ml-m4-15-amdt-4-retirement-life-of-fatigue-critical-components/important-cases","documents":"/api/acts/ad-ml-m4-15-amdt-4-retirement-life-of-fatigue-critical-components/documents"}}