{"id":"F2006B07497","name":"AD/TSA-600/33 Amdt 6 - Main Landing Gear Torque Links","slug":"ad-tsa-600-33-amdt-6-main-landing-gear-torque-links","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":49962,"registerId":"commonwealth-F2006B07497-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/TSA-600/33 Amdt 6 - Main Landing Gear Torque Links","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)  Aerostar (Piper/Ted Smith) 600 and 700 Series Aeroplanes\n\n \n\n# AD/TSA-600/33\n\nAmdt 6\n\nApplicability: All models.\n\n# Main Landing Gear Torque Links 7/97\n\n \n\nRequirement: 1. On each main landing gear torque link set, inspect the lugs at the junction of the links for fatigue cracks using the fluorescent dye penetrant method.\n\n \n\n2. Unless already accomplished, replace the nut on the link connecting bolt with a castellated nut AN 310-6 using MS 24665-302 cotter pin. If the length of link connecting bolt does not permit installation of cotter pin, replace bolt with a NAS 6606-24D bolt.\n\n \n\nNote 1: FAA AD 93-13-08 Amdt 39-8621 and Aerostar Service Bulletin 746C refer.\n\n \n\nNote 2: Installation of improved torque links in accordance with Part II of Aerostar Service Bulletin 746C, constitutes terminating action for the Requirement 1 inspection of this Directive.\n\n \n\nCompliance: 1. At the next inspection for the issue of a maintenance release in the airframe category and at each subsequent inspection for issue of a maintenance release; until improved torque links are installed in accordance with Part II of Aerostar Service Bulletin 746C.\n\n \n\n2. At the next inspection for the issue of a maintenance release in the airframe category.\n\n \n\nThe compliance of the previous issue remains unchanged except for the additional information included in the Requirement 1 compliance statement.\n\n \n\nThis Amendment becomes effective on 19 June 1997.\n\n \n\nBackground: Reports have been received of cracks developing in the main landing gear torque links. Should the torque links fail during landing, directional control of the aircraft could be lost. Reports have also been received of stripped threads on the link connecting bolt shear nut. Fitment of castellated nuts will provide increased thread engagement and positive locking.\n\n \n\nAmendment 6 is issued to introduce terminating action for the repetitive inspection requirement, by aligning this Directive with the requirement of the related FAA AD.\n\n \n\nAmendment 5 of this Airworthiness Directive became effective on 15 September 1994.\n\n \n\nAmendment 4 of this Airworthiness Directive became effective on 31 July 1986. The original issue of this Airworthiness Directive became effective on 31 July 1984.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n","sortOrder":0}],"analysis":{"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"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This Amendment 6 remains tightly scoped to its original purpose — addressing fatigue cracks and hardware deficiencies in Aerostar main landing gear torque links. The amendment introduces terminating action (allowing owners to end repetitive inspections by installing improved parts) but this is a refinement within the original safety scope, not an expansion. The document explicitly states it is aligning with the related FAA AD, indicating harmonisation rather than scope creep."},"complexity_factors":["Single aircraft type family (Aerostar 600/700 series) with straightforward applicability","Only two technical requirements: one inspection and one hardware replacement","Minimal defined terms — uses standard aviation hardware part numbers (AN 310-6, MS 24665-302, NAS 6606-24D) without requiring interpretation","Simple conditional logic: only one alternative path (if bolt too short, use different bolt)","Clear terminating action provided (installation per Service Bulletin 746C Part II ends inspection obligation)","Short document length with direct compliance dates and methods","Cross-references limited to one FAA AD and one manufacturer service bulletin for context"],"plain_english_summary":"This CASA Airworthiness Directive requires owners/operators and maintenance engineers of Aerostar 600/700 aeroplanes to address fatigue and hardware failures in main landing‑gear torque links by imposing recurring inspections and a mandatory nut/bolt upgrade to secure the linkage. It prevents possible landing‑gear separation and loss of directional control on landing. Installing the manufacturer’s improved torque links terminates the repetitive inspection requirement."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"Amendment 6 introduced an explicit terminating action by aligning the Directive with the related FAA AD and Aerostar Service Bulletin 746C (Part II). The original directive required ongoing repetitive inspections; this version adds the option to stop those recurring inspections by installing improved torque links. The change does not broaden applicability (still all Aerostar 600/700 models) but it materially alters compliance options and the long-term burden on operators by substituting recurring inspections for a one‑off retrofit."},"complexity_factors":["Short document with only two operative requirements (Requirement 1 and Requirement 2).","Single simple conditional: inspections recur until improved torque links are installed (terminating action).","One conditional parts substitution: if bolt length prevents cotter pin, bolt must be replaced with a specific bolt (NAS 6606-24D).","Cross-references to external documents: FAA AD 93-13-08 and Aerostar Service Bulletin 746C (terminating action resides in that bulletin).","Limited number of technical specifications (specific nut, cotter pin, and bolt part numbers)"],"plain_english_summary":"**What this directive does (mechanically)**\n\n- Applies to: All Aerostar (Piper/Ted Smith) 600 and 700 series aeroplanes.\n\n- Inspections (Requirement 1): At each scheduled inspection that issues a maintenance release for the airframe, maintenance personnel must inspect the lugs where the two parts of each main landing gear torque link meet for fatigue cracks. The inspection method required is the fluorescent dye penetrant test (a standard crack-detection technique).\n\n- Immediate hardware change (Requirement 2): At the next maintenance-release inspection, the nut on the link-connecting bolt must be replaced with a castellated nut AN 310-6 secured with a MS 24665-302 cotter pin. If the existing bolt is too short to accept a cotter pin, the bolt must instead be replaced with a NAS 6606-24D bolt.\n\n- Terminating action (optional one-off): If improved torque links are installed in accordance with Part II of Aerostar Service Bulletin 746C, the repetitive inspections required by Requirement 1 are no longer necessary (that installation “terminates” the inspection obligation).\n\n- Cross-references: The directive references FAA AD 93-13-08 Amdt 39-8621 and Aerostar Service Bulletin 746C for technical detail and the terminating-action procedure.\n\n**Who this affects**\n\n- Aircraft owners/operators of Aerostar 600/700 series aeroplanes: they must ensure compliance by scheduling inspections and the specified hardware changes.\n\n- Maintenance organisations and licensed aircraft maintenance engineers (AMEs): they must perform the fluorescent dye penetrant inspections, fit castellated nuts and cotter pins or replace bolts where necessary, and install improved torque links if chosen as terminating action.\n\n- Civil Aviation Safety Authority (CASA): enforces compliance with the Airworthiness Directive.\n\n**Why it matters (stated purpose and how it maps to actions)**\n\n- Stated safety concern: Reports indicated fatigue cracking in the torque link lugs and stripped threads on the link connecting bolt shear nut. Torque link failure during landing could cause loss of directional control. The directive therefore requires inspections to detect cracks and a hardware change to reduce the risk of nut/bolt failure.\n\n- How the measures are intended to address the problem:\n  - Regular dye-penetrant inspections (Requirement 1) are intended to find developing fatigue cracks before failure.\n  - Replacing the nut with a castellated nut plus cotter pin, or fitting a longer bolt if necessary (Requirement 2), increases thread engagement and provides a mechanical locking method to reduce nut loosening/stripping.\n  - Installing improved torque links per the manufacturer’s service bulletin removes the need for repeated inspections (terminating action).\n\n**Costs, incentives and trade-offs (practical effects)**\n\n- Who pays: The aircraft owner/operator pays for inspections, labour, and any parts or retrofits (castellated nuts/cotter pins, replacement bolts, or the improved torque links).\n\n- Short-term vs long-term costs:\n  - Short-term: Regular inspections impose recurring labour and aircraft downtime at every maintenance-release inspection until the terminating action is taken.\n  - One-off upgrade: Installing the improved torque links is a one-off cost that removes the recurring inspection requirement; owners will weigh the retrofit cost against ongoing inspection costs and downtime.\n\n- Implementation choices and incentives:\n  - Operators may delay the terminating-action retrofit to spread capital cost, accepting the recurring inspection burden instead.\n  - The directive forces a minimum hardware change (castellated nut/cotter pin or bolt replacement) at the next inspection, which reduces certain immediate risks regardless of whether the full retrofit is done.\n\n- Compliance burden and operational impact:\n  - Inspection method (fluorescent dye penetrant) requires disassembly/access, consumables, and skilled personnel; this raises maintenance time and possible aircraft grounding during checks.\n  - Parts availability (specified nuts, cotter pins, or NAS bolts) and access to service-bulletin parts for the terminating retrofit can affect the time to comply and cost.\n\n- Risks and failure modes:\n  - Reliability of inspections depends on proper execution (technique, cleanliness, lighting). A missed crack could still lead to failure.\n  - Incorrect installation of the cotter pin/nut or improper replacement bolts may reduce the intended safety benefit.\n\n**Concrete behavioural changes required**\n\n- Maintenance teams must add a fluorescent dye-penetrant crack check of the main landing gear torque link lugs to the routine inspection checklist for each maintenance-release inspection (Requirement 1).\n- At the next maintenance-release inspection, maintenance teams must install the specified castellated nut and cotter pin or replace the bolt if necessary (Requirement 2).\n- Owners/operators may choose to order and install the improved torque links per Aerostar Service Bulletin 746C (Part II) to stop the need for repeated inspections.\n\n**Source claims and testing them against costs and incentives**\n\n- Claim: The measures prevent torque-link failure and improve locking (stated in the directive’s Background). That claim is mechanistically credible: inspections can detect cracks before propagation; castellated nuts with cotter pins provide positive locking and increased thread engagement.\n- Trade-off: The safety benefit comes at a cost in maintenance time, parts, and potential ground time. The terminating action reduces long-run inspection costs but requires an upfront retrofit cost and parts/installation capacity.\n\n(For reference within the directive: these requirements and the terminating-action option are set out as Requirement 1, Requirement 2, and the Note referring to Part II of Aerostar Service Bulletin 746C.)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-tsa-600-33-amdt-6-main-landing-gear-torque-links","history":"/api/acts/ad-tsa-600-33-amdt-6-main-landing-gear-torque-links/history","analysis":"/api/acts/ad-tsa-600-33-amdt-6-main-landing-gear-torque-links/analysis","conflicts":"/api/acts/ad-tsa-600-33-amdt-6-main-landing-gear-torque-links/conflicts","importantCases":"/api/acts/ad-tsa-600-33-amdt-6-main-landing-gear-torque-links/important-cases","documents":"/api/acts/ad-tsa-600-33-amdt-6-main-landing-gear-torque-links/documents"}}