{"id":"F2006B08923","name":"AD/DH114/13 Amdt 6 - Centre Section and Wing Spar Boom - Fatigue Life Limitations","slug":"ad-dh114-13-amdt-6-centre-section-and-wing-spar-boom-fatigue-life-limitations","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":52483,"registerId":"commonwealth-F2006B08923-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DH114/13 Amdt 6 - Centre Section and Wing Spar Boom - Fatigue Life Limitations","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)  \nDH114 (Heron) Series Aeroplanes\n\nAD/DH114/13\n\nAmdt 6\n\nApplicability: All models.\n\n  \n\nCentre Section and Wing Spar Boom \\- Fatigue Life Limitations\n\n  \n12/89\n\nRequirement: Retire from service the centre section and wing lower spar booms.\n\nCompliance: 1. Series 1 aircraft\n\n    (a) Before Modification 492 and 520 \\- at or before 4700 hours total time in service.\n\n    (b) Centre Section lower spar booms \\- after Modification 492 \\- at or before 40,000 hours total time in service.\n\n    (c) Wing lower spar booms \\- after Modification 520 \\- at or before 20,000 hours total time in service.\n\n    2. Series 2 aircraft (All Series 2 irrespective of power plant)\n\n    (a) Before Modification 492 and 520 \\- at or before 3500 hours total time in service.\n\n    (b) After Modification 492 and 520 - at or before the total time in service as detailed in the following graph. Interpolation between the lines for different average flight times is permissible.\n\nNote 1: The total time in service detailed above for the wing spar boom includes any flying hours prior to the embodiment of Modification 520.\n\nNote 2: The Authority must be notified of any aircraft operating regularly on stages shorter than 1/2 hour duration so that an appropriate retirement life can be determined.\n\nNote 3: Series 2 aircraft fitted with wing external strap modification to STC SA3125WE are exempted from wing lower spar boom retirement.\n\nNote 4: The manufacturer has advised that the wing life cannot be extended beyond the life of the centre section spar boom, i.e. a maximum of 30000 hours for Series 2 aircraft.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.002.png)  \n\nBackground: These life limitations were established in consultation with the aircraft manufacturer, and taking into consideration Australian operating conditions and in-flight fatigue loads measurements. This Amendment follows a query received by the Authority and extends the graph to cover higher average cruise weights. The lives at lower weights remain unchanged.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This amendment remains tightly focused on its original purpose: establishing fatigue life limits for specific structural components of the DH114 Heron. Amendment 6 is a technical refinement that extends the calculation graph to cover higher average cruise weights — a responsive adjustment to operator needs without expanding the directive's scope beyond the centre section and wing spar booms."},"complexity_factors":["Multiple aircraft series (Series 1 and Series 2) with different baseline requirements","Modification-dependent compliance paths (Modifications 492 and 520) creating conditional logic","Graph-based interpolation requirement for Series 2 aircraft (referenced but not shown in text)","Cross-references to external technical documents (STC SA3125WE, Modifications 492/520)","Nested exceptions: Note 3 creates an exemption from wing spar retirement for specific modified aircraft","Operational condition triggers (short stage lengths under 1/2 hour) requiring Authority notification","Interdependent limits: Note 4 establishes a hard ceiling (30,000 hours) regardless of other calculations"],"plain_english_summary":"This CASA Airworthiness Directive mandates permanent retirement of centre section and wing lower spar booms on de Havilland DH114 Heron aircraft once specified flight-hour limits are reached, to prevent metal‑fatigue failure. It applies to owners, operators and maintenance organisations of Series 1 and 2 Herons.\n\nAmendment 6 expands the fatigue‑life calculation to cover heavier cruise weights; Series 2 with STC SA3125WE are exempt and short‑flight operators must notify CASA."},"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":true,"description":"This Amendment extends the directive's operational envelope by adding retirement-life data for higher average cruise weights (it \"extends the graph to cover higher average cruise weights\" according to the Background). The directive retains the previously established lives at lower weights, so the core safety purpose remains the same, but the amendment broadened the range of operating profiles explicitly covered by the rule. That is a modest expansion of scope: it does not change which parts or which aircraft are covered, but it alters how retirement lives are determined for a wider set of operating weights and thus affects operators who fly at higher average cruise weights."},"complexity_factors":["Multiple conditional branches by aircraft series (Series 1 vs Series 2).","Dependence on embodiment of two separate modifications (Modification 492 and Modification 520) with different effects on centre section and wing booms.","Use of an external graph to set retirement lives for Series 2 post-modification (requires averaging/interpolation and introduces operator calculation).","Explicit interpolation allowed between graph lines (introduces judgement/estimation).","Several notes creating exceptions and special processes: pre-mod hours counting (Note 1), mandatory notification for short stages (Note 2), STC-based exemption for wing booms (Note 3), manufacturer-imposed maximum (Note 4).","Cross-references to modification and STC identifiers that are external to the directive (operators must consult modification/STC documents).","Operational measurement requirements (average cruise weight, average flight time) which are not prescriptively defined in the AD and may vary by operator."],"plain_english_summary":"**What this instrument does (in plain English)**\n\n- This is an Airworthiness Directive that sets mandatory retirement (end-of-service) hours for two structural parts on de Havilland DH114 (Heron) aeroplanes: the centre section spar and the wing lower spar booms. (A spar boom is a primary structural beam in the wing/centre section.)\n\n- It applies to all DH114 models and tells operators when they must remove those parts from service, depending on aircraft series, whether certain modifications have been embodied, and accumulated flight hours.\n\n**How it works (mechanics)**\n\n- For Series 1 aircraft (see \"Compliance 1\"):\n  - If neither Modification 492 nor 520 has been fitted, retire the relevant parts at or before 4,700 total flying hours. (Compliance 1(a))\n  - After fitting Modification 492, retire the centre section lower booms at or before 40,000 total flying hours. (Compliance 1(b))\n  - After fitting Modification 520, retire the wing lower spar booms at or before 20,000 total flying hours. (Compliance 1(c))\n\n- For Series 2 aircraft (see \"Compliance 2\"):\n  - If neither Modification 492 nor 520 has been fitted, retire the parts at or before 3,500 total flying hours. (Compliance 2(a))\n  - After fitting both Modifications 492 and 520, retirement lives are set according to a graph included with the directive that varies with average flight duration and cruise weight; operators may interpolate between the lines on that graph. (Compliance 2(b))\n\n- Notes that affect compliance:\n  - Total flying hours used to determine wing spar boom life include hours accumulated before embodiment of Modification 520. (Note 1)\n  - Operators who routinely operate very short stages (less than 30 minutes) must notify the Civil Aviation Safety Authority (the Authority) so the Authority can set an appropriate retirement life. (Note 2)\n  - Series 2 aircraft fitted with an approved external wing strap modification (STC SA3125WE) are exempt from the wing lower spar boom retirement. (Note 3)\n  - The manufacturer has stated that wing life cannot exceed the life of the centre section spar boom — a maximum of 30,000 hours for Series 2 aircraft. (Note 4)\n\n**Who is affected**\n\n- Aircraft owners and operators of DH114 (Heron) aeroplanes who must monitor total airframe hours, fit the specified modifications where desired, comply with retirement schedules, and notify the regulator in special operating cases.\n- Maintenance organisations and parts suppliers who will carry out removals, repairs, or replacements and who may need to manage inventory or retrofit modifications.\n- The Civil Aviation Safety Authority, which receives notifications about short-stage operation and enforces compliance.\n\n**Why it matters (stated purpose and practical tests of that purpose)**\n\n- The directive says the retirement hours were set after consultation with the manufacturer and from Australian operational data and in-flight fatigue-load measurements (Background). The stated purpose is to prevent structural fatigue failures by removing parts before they reach unsafe fatigue life.\n\n- Practical implications and trade-offs:\n  - Who pays: Operators pay the direct costs — parts removal, replacement or retrofit, aircraft downtime, and record-keeping. Smaller operators with fewer aircraft will bear these costs without economies of scale.\n  - Incentives: There is an operational incentive to fit Modifications 492 and/or 520 (or the external strap STC for Series 2) because doing so extends the allowable hours before retirement. That creates a clear trade-off: incur retrofit cost now to get longer operational life later. (Compliance 1–2, Notes 3–4)\n  - Compliance burden: The rule requires accurate tracking of total time-in-service, knowledge of whether relevant modifications have been embodied, and, for some operators, reporting to the Authority (Note 2). The Series 2 post-mod rule depends on a graph keyed to average flight durations and cruise weights, which requires operators to calculate or estimate average flight times/weights and potentially interpolate between lines. (Compliance 2(b))\n  - Implementation risks and ambiguity: The directive relies on an external graph (not reproduced in full here) and allows interpolation, which creates room for interpretation about what precise retirement life applies to a particular operating profile. The Authority must be notified for short-stage ops so it can set an \"appropriate retirement life,\" delegating some discretion to the regulator. (Compliance 2(b); Note 2)\n  - Operational substitutions: Operators may change routing, payload, or stage length to alter average flight time/weight profiles if that reduces fatigue accumulation, but any change requires accurate record-keeping and may have commercial costs.\n  - Concentrated benefits vs diffuse costs: Operators who retrofit early benefit from longer lives; the costs (retirement, retrofits, downtime) are borne by the operator community in aggregate rather than by the manufacturer or regulator. The manufacturer’s statement that wing life cannot exceed centre section life caps one possible advantage of retrofits for wings. (Note 4)\n\n**Immediate compliance actions for operators**\n\n- Check each DH114’s series and record of Modifications 492/520 and STC SA3125WE.\n- Calculate total time-in-service for centre section and wing lower spar booms (including hours before modifications where required). (Note 1)\n- If regularly flying stages under 30 minutes, notify the Authority so it can set an appropriate retirement life. (Note 2)\n- Plan for part retirement, replacement, or retrofit well before the listed hours to avoid unplanned groundings.\n\n**Sources in the instrument**\n- Compliance paragraphs for Series 1 and Series 2; Notes 1–4; Background paragraph regarding consultation and flight-load data."},"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-dh114-13-amdt-6-centre-section-and-wing-spar-boom-fatigue-life-limitations","history":"/api/acts/ad-dh114-13-amdt-6-centre-section-and-wing-spar-boom-fatigue-life-limitations/history","analysis":"/api/acts/ad-dh114-13-amdt-6-centre-section-and-wing-spar-boom-fatigue-life-limitations/analysis","conflicts":"/api/acts/ad-dh114-13-amdt-6-centre-section-and-wing-spar-boom-fatigue-life-limitations/conflicts","importantCases":"/api/acts/ad-dh114-13-amdt-6-centre-section-and-wing-spar-boom-fatigue-life-limitations/important-cases","documents":"/api/acts/ad-dh114-13-amdt-6-centre-section-and-wing-spar-boom-fatigue-life-limitations/documents"}}