{"id":"F2006B08517","name":"AD/CFM56/12 - Accessory and Transfer Gearbox Replacement","slug":"ad-cfm56-12-accessory-and-transfer-gearbox-replacement","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":51254,"registerId":"commonwealth-F2006B08517-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CFM56/12 - Accessory and Transfer Gearbox Replacement","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 106 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nCFM International Turbine Engines \\- CFM56 Series\n\nAD/CFM56/12 Accessory and Transfer Gearbox Replacement\n\n  \n6/98 TX\n\nApplicability: CFM International (CFMI) CFM56-3, all models, turbofan engines with serial numbers as listed below (Warning: some engines may appear in more than one list):\n\nList 1A: (First batch of CFM56-3 engines with suspect starter gearshaft (line 5) in the accessory gearbox): Engine Serial Number (ESN): 858619 to 858622, 858624, 858627 to 858635, 858638, 858640, 858641, 858644, 858647, 858657 (See Service\n\nBulletin CFM56-3/ \\-3B/ \\-3C S/B 72-863 revision 1).\n\nList 1B: (Second batch of CFM56-3 engines with suspect starter gearshaft (line 5) in the accessory gearbox): ESN: 858639, 858642, 858643, 858646, 858648 to 858656,\n\n858658, 858660, 858662 to 858665, 858670, 858671, 858673, 858676, 858678 (See\n\nService Bulletin CFM56-3/ \\-3B/ \\-3C S/B 72-863 revision 1).\n\nList 2A: (CFM56-3 Engines with suspect 26 teeth input bevel gear (line 1) in the transfer gear box). ESN: 858568, 858571, 858576, 858624, 858625, 858630 to\n\n858639, 858641 to 858643, 858646 to 858651, 858654 to 858657, 858660 to 858662,\n\n858665 to 858668, 858673, 858687, 858688, 858701, 722201 (See Service Bulletin CFM56-3/ -3B/ -3C S/B 72-865).\n\nList 2B: (CFM56-3 Engines with suspect 27 teeth output bevel gear (line 2) in the transfer gear box): ESN: 858635 to 858637, 858642, 858643, 858646, 858648,\n\n858656, 858657, 858662, 858663, 858665 to 858669, 858671 to 858677, 858679 to\n\n858681, 858684, 858686, 858688, 858689, 858691, 858700 (See Service Bulletin CFM56-3/ -3B/ -3C S/B 72-865).\n\nList 3: (CFM56-3 engines with suspect intermediate gearshaft 44x73 teeth (line 9)in the accessory gearbox). ESN 858619 to 858622, 858624, 858627 to 858642, 858644\n\nto 858652, 858654, 858657 to 858660, 858666, 858668. (See Service Bulletin CFM56-3/ -3B/ -3C S/B 72-873 Revision 1).\n\nRequirement: 1. For all engines in Lists 1A, 1B, 2A and 2B above, check the AGB and TGB magnetic chip detector (MCD). If magnetic particles are found, remove the AGB and TGB from service in accordance with Service Bulletin CFM56-3/ -3B/ -3C S/B 72-A861 Revision 3.\n\n    2. For all engines in Lists 1A and 1B, remove from service the starter gearshaft in the AGB in accordance with Service Bulletin CFM56-3/ -3B/ -3C S/B 72-863 Revision 1.\n\n    3. For all engines in List 2A, remove from service the input bevel gearshaft in the TGB in accordance with Service Bulletin CFM56-3/ -3B/ -3C S/B 72-865.\n\n    4. For all engines in List 2B, remove from service the output bevel gearshaft in the TGB in accordance with Service Bulletin CFM56-3/ -3B/ -3C S/B 72-865.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 106 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n    5. For all engines in List 3, remove from service the intermediate gearshaft cluster (44x73 teeth) in the AGB in accordance with Service Bulletin CFM56-3/ \\-3B/ \\- 3C S/B 72-873.\n\n    6. For twin engined aircraft which have both engines in one or more of the applicability lists, all the suspect gearshafts (as identified in items 2 \\- 5 above) on one engine must be replaced.\n\nNote 1: Actions listed above which have already been completed under AD/CFM- 56/8 need not be repeated under this directive.\n\nNote 2: DGAC T98-096 (B) dated 25 February 1998 refers.\n\nCompliance: 1. Daily.\n\n    2. For engines in List 1A, before 20 December 1997. For engines in List 1 B, before 20 January 1998.\n\n    3. Before 20 December 1997.\n\n    4. Before 20 January 1998.\n\n    5. Before 15 April 1998.\n\n    6. Before next flight.\n\nThis airworthiness directive becomes effective on 26 March 1998.\n\nBackground: Three in flight shut downs were experienced due to failure of starter gearshafts in the accessory gearbox (AGB). The first analysis results shows also a risk of failure of the conical gearshafts of the transfer gearbox (TGB) which could lead to an in flight shut down. This directive supersedes the CFM56-3 requirements of AD/CFM-56/8 which has been cancelled.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":true,"description":"Yes. This directive expands and modifies the scope beyond the earlier AD/CFM-56/8 it supersedes. The current text extends mandatory actions to additional gearbox components (not only the starter gearshaft in the accessory gearbox but also certain conical bevel gearshafts in the transfer gearbox and an intermediate gearshaft cluster), lists additional engine serial numbers across five lists, and imposes daily magnetic chip detector checks plus an immediate replacement requirement for twin‑engine aircraft where both engines are affected (Requirement 6). It therefore broadens the set of components and engines subject to mandatory removal/replacement and tightens operational constraints compared with the prior AD (Note 1; Background; Requirements 1–6)."},"complexity_factors":["Five separate applicability lists (Lists 1A, 1B, 2A, 2B, 3) each containing multiple engine serial numbers","Multiple distinct mandatory actions tied to different lists (daily MCD checks; removal of starter gearshaft; removal of input/output bevel gearshafts; removal of intermediate gearshaft cluster)","Different compliance deadlines for each action/list (daily checks plus several date‑specific deadlines)","Cross-reference to and reliance on multiple manufacturer service bulletins (S/B 72-A861 Rev 3, S/B 72-863 Rev 1, S/B 72-865, S/B 72-873 Rev 1) for the required technical procedures","Special operational rule for twin‑engine aircraft where both engines appear on lists (Requirement 6) imposing immediate pre‑flight replacement","Note referencing a prior AD (AD/CFM‑56/8) with exceptions for work already completed (adds cross‑AD logic)","Moderate number of defined items (AGB, TGB, MCD, specific gear types) though not heavy legal drafting or nested exceptions"],"plain_english_summary":"**What this directive does (mechanically)\n\n- Identifies specific CFM56-3 turbofan engines (by engine serial number lists) that have certain suspect gears in their accessory gearbox (AGB) or transfer gearbox (TGB).\n- Requires daily inspections of the accessory gearbox (AGB) and transfer gearbox (TGB) magnetic chip detectors (MCDs). If any magnetic particles are found, the affected gearbox must be removed from service and handled according to the manufacturer's service bulletin (Requirement 1).\n- Requires removal (and replacement) of particular suspect gear components from engines on the specified lists, in accordance with the CFM service bulletins cited:\n  - Starter gearshaft in the AGB for engines in Lists 1A and 1B (Requirement 2).\n  - Input bevel gearshaft in the TGB for engines in List 2A (Requirement 3).\n  - Output bevel gearshaft in the TGB for engines in List 2B (Requirement 4).\n  - Intermediate gearshaft cluster (44x73 teeth) in the AGB for engines in List 3 (Requirement 5).\n- For twin‑engine aircraft where both engines appear on one or more of these lists, all suspect gearshafts on one engine must be replaced before further flight (Requirement 6).\n- Sets specific deadlines for the required removals and inspections (different dates for different lists and the daily MCD check). Actions already completed under the earlier AD/CFM-56/8 are not required to be repeated (Note 1).\n\nWho this affects\n\n- Operators and owners of aircraft powered by the listed CFM56-3 engines (those specific engine serial numbers in Lists 1A, 1B, 2A, 2B and 3).\n- Maintenance organisations, airlines, and MROs responsible for inspections and component replacement.\n- CFM International as the supplier of the service bulletins and replacement parts.\n\nWhy it matters (official rationale, then practical implications)\n\n- Official reason: The manufacturer and regulator identified in‑flight shutdowns caused by starter gearshaft failures in the AGB and a risk that certain bevel (conical) gearshafts in the TGB could also fail and cause in‑flight shutdowns. The AD is intended to remove suspect components before they fail (Background).\n\n- Practical implications and trade‑offs:\n  - Safety mechanism: mandatory daily checks and mandatory removal/replacement of identified suspect gears reduce the short‑term risk of in‑flight engine shutdown caused by those parts (Requirements 1–5).\n  - Who pays: the operators/owners bear the direct costs — inspections, shop labour, parts, and aircraft downtime. CFM (the engine manufacturer) supplies the service bulletins that prescribe the work and supplies replacement parts.\n  - Who decides and who acts: the Civil Aviation Safety Authority (via this AD) imposes the requirement; the engine manufacturer specifies the technical procedures in service bulletins; operators and licensed maintenance organisations perform the work.\n  - Behavioural change: operators must add a daily MCD check to maintenance routines for affected engines, schedule removal/repair of engines and gearshafts by the specified deadlines, and may ground or restrict aircraft until compliance. For twin‑engine aircraft with both engines affected, operators must replace all suspect gearshafts on one engine before flight, raising the immediacy of compliance for those aircraft (Requirement 6).\n  - Costs and capacity: the requirement concentrates costs on operators of the affected serial numbers and may create demand pressure for replacement parts and MRO capacity (potentially lengthening downtime). There is an administrative/compliance burden: recordkeeping, tracking which engines are affected, and coordination with MROs.\n  - Substitution and operational effects: operators may delay removal only at the risk of safety and regulatory non‑compliance; affected aircraft may be taken out of service temporarily, affecting flight schedules and revenue. Maintenance shops and the OEM may see increased business from repairs and parts supply.\n  - Implementation risk: effectiveness depends on accurate identification of engine serial numbers, timely availability of parts and qualified labour, and consistent performance of daily MCD inspections. If parts or shop slots are scarce, operators face trade‑offs between grounding aircraft and operational disruption.\n\nLegal mechanics to note\n\n- Compliance is mandatory and time‑bound: daily checks plus fixed deadlines for replacement depending on which list an engine appears in (Compliance section).\n- The AD refers to specific CFM service bulletins for the detailed removal/replacement procedures; following those bulletins is the required method (Requirements 1–5).\n- Actions already completed under the prior AD (AD/CFM-56/8) need not be repeated (Note 1).\n\nSource claims vs costs and trade‑offs\n\n- The directive claims it reduces the risk of in‑flight shutdowns by removing suspect parts (Background). That safety benefit requires operators to absorb the direct costs and operational impacts described above (Requirements & Compliance). The directive centralises technical decisions to the OEM's service bulletins (which define the procedure), while the regulatory authority mandates timing and scope (Requirements 1–6, Compliance)."},"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":4,"scope_assessment":{"changed":false,"description":"This directive maintains its original scope as a targeted safety intervention for specific defective engine components. It replaces an earlier directive (AD/CFM-56/8) but does not expand beyond the original purpose of addressing gearbox failures in CFM56-3 engines. The expansion from starter gearshafts to include transfer gearbox components reflects evolving safety intelligence rather than scope creep."},"complexity_factors":["Multiple applicability lists (1A, 1B, 2A, 2B, 3) with overlapping serial numbers requiring cross-referencing","Six distinct compliance requirements with different deadlines (ranging from 'daily' to specific dates)","Technical terminology requiring aviation engineering knowledge (AGB, TGB, MCD, gearshaft specifications like '44x73 teeth')","Reference to four external service bulletins that must be consulted for actual replacement procedures","Conditional logic: twin-engine aircraft have additional requirements (item 6) beyond single-engine requirements","Nested applicability: some engines appear in multiple lists, triggering multiple requirements","Supersedes previous directive (AD/CFM-56/8) with partial credit for work already completed (Note 1)"],"plain_english_summary":"This CASA airworthiness directive orders operators of Boeing 737s with certain CFM56‑3 engines to inspect for and replace defective gearbox parts after in‑flight failures from broken gearshafts. It mandates routine chip‑detector checks and timely part replacement for affected serial-numbered engines. The rule protects against engine shutdowns in flight and updates an earlier, narrower safety order."}},"importantCases":[],"_links":{"self":"/api/acts/ad-cfm56-12-accessory-and-transfer-gearbox-replacement","history":"/api/acts/ad-cfm56-12-accessory-and-transfer-gearbox-replacement/history","analysis":"/api/acts/ad-cfm56-12-accessory-and-transfer-gearbox-replacement/analysis","conflicts":"/api/acts/ad-cfm56-12-accessory-and-transfer-gearbox-replacement/conflicts","importantCases":"/api/acts/ad-cfm56-12-accessory-and-transfer-gearbox-replacement/important-cases","documents":"/api/acts/ad-cfm56-12-accessory-and-transfer-gearbox-replacement/documents"}}