{"id":"F2006B10046","name":"AD/G1159/42 - DC Essential Bus Indication","slug":"ad-g1159-42-dc-essential-bus-indication","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":55475,"registerId":"commonwealth-F2006B10046-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"AIRWORTHINESS DIRECTIVE","sectionType":"part","heading":"AIRWORTHINESS DIRECTIVE","content":"# ![](image.001.png)  \nAIRWORTHINESS DIRECTIVE\n\nFor the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CASR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.\n\n![](image.001.png)  \n\nGulfstream (Grumman) G1159 and G-IV Series Aeroplanes","sortOrder":0},{"sectionNumber":"AD/G1159/42 DC Essential Bus Indication ","sectionType":"part","heading":"AD/G1159/42 DC Essential Bus Indication 8/2004","content":"# AD/G1159/42 DC Essential Bus Indication 8/2004\n\nApplicability: Model G-IV series aeroplanes, serial numbers 1000 through 1359 inclusive. Requirement: 1. For aeroplanes equipped with the SPZ 8400 Digital Integrated Flight\n\nControl System, accomplish the following, as applicable:\n\n    If the aeroplane has the production equivalent of Gulfstream IV Aircraft Service Change (ASC) 327, install the new indicator light and the audible tone, in accordance with Gulfstream GIV Customer Bulletin 102B, dated 26 January 2004, together with Modification Instructions A, J through L, and P through S of Gulfstream IV ASC 327B, dated 26 January 2000.\n\n    b. If the aeroplane has Gulfstream IV ASC 327 installed, but not Gulfstream IV ASC 327A, install the new indicator light and the audible tone, in accordance with Gulfstream GIV Customer Bulletin 102B; Modification Instructions A through H of Gulfstream GIV ASC 327B Am2, dated 26 January 2004; and Modification Instruction P of Gulfstream IV ASC 327B.\n\nNote 1: Modification Instruction E in Gulfstream GIV ASC 327B Am2 is the same as Modification Instruction P in Gulfstream IV ASC 327B.\n\n    c. If the aeroplane has Gulfstream IV ASC 327A installed, ensure that all ground wires from connectors 95A1P2B and 95A2P2B are removed or rerouted in accordance with Gulfstream GIV Customer Bulletin 102B and Figure 6 of Gulfstream IV ASC 327B.\n\n    2. For aeroplanes not equipped with the SPZ 8400, accomplish the following, as applicable:\n\n    If the aeroplane does not have Gulfstream IV ASC 327 installed, install the new indicator light and the audible tone, in accordance with Gulfstream GIV Customer Bulletin 102B; together with Modification Instructions A, B through I, and P through S of Gulfstream IV ASC 327B.\n\n    b. If the aeroplane has Gulfstream IV ASC 327 installed, install the new indicator light and the audible tone, in accordance with Gulfstream GIV Customer Bulletin 102B, together with Modification Instructions A, M through O, and P through S of Gulfstream IV ASC 327B.","sortOrder":1}],"analysis":{"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":false,"description":"This AD remains focused on correcting an identified unsafe condition for a specific fleet (Gulfstream G‑IV serial numbers 1000–1359) by requiring installation of a DC essential bus indicator and associated audible tone or specified wiring changes. It does not expand regulatory scope beyond remediating that safety issue or impose wider obligations on other aircraft types. The directive sets technical obligations tied directly to aircraft configuration and referenced Gulfstream modification instructions, consistent with the typical purpose and scope of an airworthiness directive."},"complexity_factors":["Conditional structure with two main branches (SPZ‑8400 equipped vs not) and additional sub‑conditions based on installed ASCs (ASC 327, 327A, ASC 327B variants)","Cross‑references to multiple external technical documents: Gulfstream GIV Customer Bulletin 102B; Gulfstream IV ASC 327B and its amendment files (Am2, etc.)","Multiple specific modification instruction sets referenced (A, B–I, J–L, M–O, P–S) requiring reading and following different subsets depending on configuration","Technical wiring work (removal/rerouting of ground wires) that requires precision and configuration verification","Applicability limited to a defined serial number range (1000–1359), so operators must check individual airframe records","Note that one modification instruction is stated equivalent to another (Note 1), creating an extra interpretive step","Absence of the compliance time in the provided excerpt (requires consulting the full AD)","Dependence on accurate historical installation records to choose the correct compliance path"],"plain_english_summary":"**What this directive does (mechanics)\n\n- Applies to Gulfstream (Grumman) G-IV series aeroplanes with serial numbers 1000 through 1359 (Applicability).\n- Requires installation of a new DC \"essential bus\" indicator lamp and an audible tone (a cockpit warning), or appropriate wiring changes, depending on the aeroplane's existing flight‑control equipment and previous Gulfstream modifications (Requirement 1 and 2).\n- The AD divides affected aeroplanes into two paths: those equipped with the SPZ‑8400 Digital Integrated Flight Control System (Requirement 1) and those without it (Requirement 2). Each path tells you which Gulfstream modification instructions and customer bulletin to follow to install the indicator and tone.\n- If a particular earlier modification (Gulfstream IV ASC 327A) is already installed, the AD instead requires removal or rerouting of specific ground wires from connectors 95A1P2B and 95A2P2B (Requirement 1.c), per the Gulfstream instructions.\n- The AD repeatedly requires compliance with external Gulfstream technical documents: Gulfstream GIV Customer Bulletin 102B and various modification instructions in Gulfstream IV ASC 327B (and its amendments). Note 1 explains one modification instruction is equivalent to another.\n- The excerpt does not include the compliance time window (the AD text says compliance timing is given in the compliance section, which is not present here).\n\nWho this affects\n\n- Aircraft owners and operators of the specified Gulfstream G‑IV serial numbers.\n- Approved maintenance organisations and certificated engineers who must perform the work.\n- Airlines or charter operators who will incur parts, labour and downtime costs while the modifications are installed.\n\nWhy it matters (stated purpose and practical effect)\n\n- The AD is issued by the Civil Aviation Safety Authority (CASA) delegate under CASR subregulation 39.1(1) to correct an identified unsafe condition. Its stated purpose is to ensure the cockpit provides a reliable visual and audible indication related to the DC essential bus.\n- Practically, the AD forces a technical change to the aircraft electrical/avionics system so flightcrew have the additional indication and warning tone required by CASA.\n\nCosts, incentives and implementation trade‑offs\n\n- Who pays: the aircraft owner/operator pays for parts, approved components and labour, plus aircraft downtime while the work is done (Requirement 1 & 2 references to Gulfstream instructions).\n- Who decides: CASA requires the modification; operators decide scheduling and selection of a qualified maintenance provider. The specific work must follow the referenced Gulfstream bulletins and modification instructions, so compliance is constrained by those documents.\n- Compliance burden: operators must determine their aircraft configuration (SPZ‑8400 presence and which ASCs are installed) and then follow the corresponding, potentially different, modification instructions. This requires access to Gulfstream technical documents and possibly different parts or wiring changes depending on configuration.\n- Implementation risk: multiple cross‑referenced modification versions and the conditional paths increase the chance of configuration‑selection errors (for example, misidentifying whether ASC 327 or ASC 327A is installed), which could lead to incomplete compliance or the unsafe condition persisting. Routing or removal of ground wires is a precise wiring task—errors could create new electrical problems if done incorrectly.\n- Market effects and incentives: the AD imposes a one‑time compliance cost on a defined fleet. It does not create ongoing fees or alter ownership rights, but it constrains maintenance choice to work that achieves the required configuration (and authorised parts/techniques per Gulfstream documents).\n\nConcrete mechanics to comply (steps operators will follow)\n\n1. Identify the aeroplane serial number and whether it has the SPZ‑8400 flight control system and which Gulfstream ASCs (327, 327A, 327B) are installed (Applicability; Requirement 1 & 2).\n2. Follow the specific set of Gulfstream modification instructions and Customer Bulletin 102B named in the matching requirement paragraph to install the new indicator lamp and audible tone, or reroute/remove ground wires where instructed.\n3. Record the modification in the aircraft maintenance logbooks and retain the Gulfstream documents used to accomplish the work for regulatory audit.\n\nLimitations of the excerpt\n\n- The compliance time (when the work must be completed) and any details about approval of alternate means of compliance are not included in the excerpt, so operators must consult the full AD for timing and any additional administrative requirements.\n\nKey text references: Applicability; Requirement 1 (SPZ‑8400 equipped) and 2 (not SPZ‑8400); Note 1 (instruction equivalence)."},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This AD maintains its original narrow scope — mandating specific safety modifications to address a defined unsafe condition in a particular aircraft type. The conditional structure reflects necessary technical variations rather than scope creep."},"complexity_factors":["Multiple conditional branches based on aircraft configuration (SPZ 8400 system presence, ASC 327/327A installation status)","Cross-references to external technical documents (Gulfstream Customer Bulletin 102B, ASC 327B, ASC 327B Am2) without reproducing their content","Alphanumeric modification instruction references (A, B-I, J-L, M-O, P-S) that require external lookup","Nested applicability conditions creating four distinct compliance paths","Technical aviation terminology requiring domain knowledge (e.g., 'DC Essential Bus', 'connectors 95A1P2B', 'ground wires')"],"plain_english_summary":"This AD requires specified Gulfstream G‑IV series jets (S/N 1000–1359) to be modified with a new warning light and audible alarm to alert pilots to DC Essential Bus failure or abnormal operation. It applies to owners, operators, and maintenance organisations.\n\nIt matters because the DC Essential Bus powers critical flight instruments and systems; the mandated alerts give crews immediate notice to respond and reduce the risk of unsafe flight or loss of control."},"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-g1159-42-dc-essential-bus-indication","history":"/api/acts/ad-g1159-42-dc-essential-bus-indication/history","analysis":"/api/acts/ad-g1159-42-dc-essential-bus-indication/analysis","conflicts":"/api/acts/ad-g1159-42-dc-essential-bus-indication/conflicts","importantCases":"/api/acts/ad-g1159-42-dc-essential-bus-indication/important-cases","documents":"/api/acts/ad-g1159-42-dc-essential-bus-indication/documents"}}