{"id":"F2006B11137","name":"AD/LEARJET/20 - Upper Cabin Door Lock Mechanism Bolts - Modification","slug":"ad-learjet-20-upper-cabin-door-lock-mechanism-bolts-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":56821,"registerId":"commonwealth-F2006B11137-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/LEARJET/20 - Upper Cabin Door Lock Mechanism Bolts - Modification","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)  Gates Learjet 24 & 25 Series Aeroplanes\n\n \n\n# AD/LEARJET/20 Upper Cabin Door Lock Mechanism\n\nBolts - Modification\n\nApplicability: All model 24 with S/Nos. 24-100 to 24-357,\n\n \n\nAll model 25 with S/Nos. 25-003 to 25-291.\n\n# 3/80\n\n \n\nRequirement: Modify the upper cabin door lock mechanism bolts by installing Gates Learjet Kit No. AMK 79-9.\n\n \n\nCompliance: Within 150 hours time in service after 30 April 1980.\n\n \n\nBackground: Modification kit AMK 79-9 provides an additional safety feature to the upper cabin door lock mechanism by installing drilled bolts and lockwiring these bolts in situ.\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\n \n\n \n\n \n\n \n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, single-purpose airworthiness directive focused on a specific mechanical modification. It has not expanded beyond its original safety purpose."},"complexity_factors":["Single, unambiguous requirement with no conditional logic","Only 2 defined applicability criteria (aircraft model and serial number ranges)","No cross-references to other legislation or regulations","Straightforward compliance deadline (150 hours time in service after fixed date)","No exceptions, exemptions, or nested provisions","Extremely short document (approximately 150 words of substantive content)"],"plain_english_summary":"This is an **Airworthiness Directive** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) that requires specific repairs or modifications to aircraft.\n\n**What it does:**\nOrders owners and operators of certain Gates Learjet 24 and 25 series aircraft to install a safety modification kit (called \"AMK 79-9\") on the upper cabin door lock mechanism.\n\n**Who it affects:**\n- All Learjet Model 24 aircraft with serial numbers 24-100 through 24-357\n- All Learjet Model 25 aircraft with serial numbers 25-003 through 25-291\n\n**What the fix involves:**\nReplacing or modifying the bolts in the upper cabin door lock with special \"drilled bolts\" that are then secured with lockwire (a safety wire that prevents bolts from loosening due to vibration).\n\n**When it must be done:**\nWithin 150 hours of flight time after 30 April 1980.\n\n**Why it matters:**\nThis prevents the upper cabin door from potentially opening in flight due to bolt failure — a serious safety risk. The lockwire provides a backup safety feature if the bolts were to loosen."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The directive applies to a defined set of Learjet 24 and 25 serial numbers and prescribes a single, specified modification (installation of Kit AMK 79-9) within a fixed compliance period. The text provides no evidence that the scope departs from its original stated purpose (adding a drilled-and-lockwired bolt feature to the upper cabin door lock mechanism); therefore there is no indication in the instrument itself that the scope has changed from its originally stated intent. (See \"Applicability\", \"Requirement\", and \"Background\".)"},"complexity_factors":["Narrow applicability: limited to specific serial-number ranges of two models (See \"Applicability\").","Single specified technical action: install a named kit (AMK 79-9) to modify bolts (See \"Requirement\" and \"Background\").","Clear, short compliance window: 150 hours time in service after a fixed date (See \"Compliance\").","Prescriptive remedy leaves little procedural discretion but requires procurement and mechanical work (See \"Requirement\" and \"Background\").","Implementation risks tied to correct mechanical installation and scheduling of maintenance (inferred from \"Background\" and \"Requirement\")."],"plain_english_summary":"### What this directive does\n\nThis Airworthiness Directive (AD/LEARJET/20) requires that specified Gates Learjet 24 and 25 series aeroplanes be modified by installing Gates Learjet Kit No. AMK 79-9 to the upper cabin door lock mechanism bolts. The Civil Aviation Safety Authority (CASA) issued the directive under the Commonwealth Civil Aviation Regulations schedule of Airworthiness Directives. (See header and \"Requirement\"/\"Applicability\".)\n\n### Who it affects\n\n- Owners/operators of Learjet model 24 (S/N 24-100 to 24-357) and model 25 (S/N 25-003 to 25-291). (See \"Applicability\".)\n- Maintenance organisations or mechanics who perform the modification. (See \"Requirement\".)\n\n### What must be done, and by when\n\n- Install Gates Learjet Kit No. AMK 79-9 to modify the upper cabin door lock mechanism bolts. (See \"Requirement\".)\n- Complete the modification within 150 hours time in service after 30 April 1980. (See \"Compliance\".)\n\n### Why the change is required\n\n- The stated purpose of kit AMK 79-9 is to provide an additional safety feature by installing drilled bolts and lockwiring these bolts in situ to the upper cabin door lock mechanism. (See \"Background\".)\n\n### Who pays and what behaviour changes\n\n- The directive places the compliance obligation on the owners/operators of the affected aircraft (they must arrange and pay for the kit and the installation). (Inference from \"Applicability\" and \"Requirement\".)\n- Maintenance providers must perform the specified mechanical modification (drilling and lockwiring of bolts using the specified kit). (See \"Requirement\" and \"Background\".)\n\n### Compliance burden and timing\n\n- The directive is mandatory for the listed serial-numbered aeroplanes and sets a fixed compliance window: 150 hours time in service after 30 April 1980. Operators must plan maintenance, procurement of the kit, and aircraft downtime within that window. (See \"Compliance\" and \"Requirement\".)\n\n### Implementation and risk considerations (practical mechanics, trade-offs)\n\n- The technical change is concrete: installation of a parts kit that modifies the existing bolt arrangement by drilling and lockwiring. (See \"Background\" and \"Requirement\".)\n- Costs to operators will include acquiring Kit AMK 79-9 and paying for labour and any consequential downtime while the aircraft is modified. (Implied by the requirement to install the kit.)\n- The directive is prescriptive rather than permissive: it specifies the exact kit and a compliance deadline, leaving little operational discretion about method or timing beyond meeting the deadline. (See \"Requirement\" and \"Compliance\".)\n- The stated safety benefit depends on correct installation of the drilled bolts and lockwiring; incorrect installation would risk failing to achieve the intended safety feature. (Inferred from the nature of the mechanical modification described in \"Background\".)\n\n### Summary of incentives and trade-offs\n\n- Incentive for operators is to invest in the specified kit and installation to meet the mandatory AD and achieve the stated safety enhancement. (See \"Requirement\" and \"Background\".)\n- Costs and operational disruptions fall on aircraft owners/operators, concentrated on those holding the listed serial-numbered aircraft. (See \"Applicability\" and \"Requirement\".)\n- The directive reduces choice over whether and how to address the particular safety concern by mandating a specific kit and method within a set time window. (See \"Requirement\" and \"Compliance\".)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-learjet-20-upper-cabin-door-lock-mechanism-bolts-modification","history":"/api/acts/ad-learjet-20-upper-cabin-door-lock-mechanism-bolts-modification/history","analysis":"/api/acts/ad-learjet-20-upper-cabin-door-lock-mechanism-bolts-modification/analysis","conflicts":"/api/acts/ad-learjet-20-upper-cabin-door-lock-mechanism-bolts-modification/conflicts","importantCases":"/api/acts/ad-learjet-20-upper-cabin-door-lock-mechanism-bolts-modification/important-cases","documents":"/api/acts/ad-learjet-20-upper-cabin-door-lock-mechanism-bolts-modification/documents"}}