{"id":"F2006B10757","name":"AD/HU 369/93 - Main Transmission Gear Replacement","slug":"ad-hu-369-93-main-transmission-gear-replacement","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":56205,"registerId":"commonwealth-F2006B10757-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/HU 369/93 - Main Transmission Gear Replacement","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)  \nMcDonnell Douglas (Hughes) and Kawasaki 369 Series Helicopters\n\nAD/HU 369/93 Main Transmission Gear Replacement 11/97\n\nApplicability: All Model 369D, E, F, FF, 500N, AH-6 and MH-6 helicopters with main rotor transmission part number (P/N) 369D25100 installed.\n\nRequirement: 1. Determine if the installed transmission output drive gear, P/N 369D25127-11, has a serial number (S/N) in the range S/N 005570-0646 thru S/N 005570-0765 or S/N 005570-0876 thru' S/N 005570-0998. This may be achieved by inspection of records, contact with the manufacturer or by direct inspection through the open liquid level plug port (MDHS Service Information Notice DN-189/EN82/FN- 69/NN-009 dated Jan 10, 1997 refers).\n\n2. If the gear proves to be one of the affected S/N listed above, the gear is to be replaced with an airworthy gear with a S/N other than those listed at 1. above in accordance with the compliance summary below.\n\nNote: FAA AD 97-15 \\-08 amendment 39-10081 refers.\n\nCompliance: 1. Within the next 10 hours time in service after the effective date of this directive identify the gear serial number.\n\n    2. Gears identified in requirement 1 above are to be replaced as follows:\n\n    For helicopters equipped with a cargo hook assembly, with a separate, permanently maintained log of actual hours time in service (TIS) of external load operation, remove and replace the gear within the next 25 hours TIS for external load operations, or within 400 hours TIS for non-external load operations, whichever comes first.\n\n    b. For helicopters equipped with a cargo hook assembly with no separate, permanently maintained log of actual external load operation, remove and replace the gear within the next 25 hours TIS after the effective date of this directive. Owners/operators may elect to begin maintaining a separate permanent log of external load operations from the effective date of this directive and then comply with the requirements of 2(a) of this AD.\n\n    c. For helicopters without cargo hook assemblies, remove and replace the gear within the next 400 hours TIS after the effective date of this directive.\n\n    3. There are no follow on inspections or maintenance requirements once the gear has been replaced as required above.\n\nBackground: Several reports of spalled or fractured gear teeth of the output transmission drive of the affected aircraft have lead to the generation of this Directive to identify and replace certain gear serial numbers. The defect was traced to a quality control problem within the gear manufacturing process and the affected batches have been traced.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This is a targeted safety directive addressing a specific manufacturing defect in a specific part. The scope remains precisely limited to the identified defective gears and has not expanded beyond the original safety purpose."},"complexity_factors":["Multiple conditional compliance paths based on equipment configuration (cargo hook presence) and record-keeping practices","Nested serial number ranges requiring precise identification (three separate ranges with gaps: 005570-0646 thru 005570-0765, and 005570-0876 thru 005570-0998)","Cross-reference to FAA AD 97-15-08 and manufacturer service notice (MDHS Service Information Notice DN-189/EN82/FN-69/NN-009)","Technical aviation terminology requiring specialized knowledge (P/N, S/N, TIS, spalled, external load operations)","Dual timeline calculation method (external load hours vs. total time in service) with 'whichever comes first' logic"],"plain_english_summary":"This CASA Airworthiness Directive requires operators of Hughes/McDonnell Douglas 369-series helicopters with main transmission P/N 369D25100 to inspect for specified serial-numbered gears and replace any defective units within strict, usage-dependent flying-hour limits. \n\nIt matters because a manufacturing defect can cause gear teeth to spall or fracture, risking catastrophic loss of main transmission power—particularly urgent for helicopters used in external-load operations."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"This directive remains narrowly focused on identifying and replacing specific defective main transmission output drive gear batches. It enforces immediate inspection and time-limited replacement windows tied to operational use and recordkeeping. It does not broaden the regulatory scope beyond the original safety-remedy purpose (identification and removal of parts from defective manufacturing batches)."},"complexity_factors":["Short, single-subject airworthiness directive (limited length).","Limited number of defined technical identifiers (P/N, S/N, TIS) but these are critical to compliance.","Conditional compliance structure with three branches depending on presence of cargo hook and recordkeeping (Compliance 2a–2c).","Tight initial action window (inspect within 10 hours TIS) plus differing replacement thresholds (25 hours vs 400 hours).","Option to elect a new recordkeeping regime (start a separate external-load log) which changes the applicable compliance timetable (creates administrative choice).","Two non-contiguous serial-number ranges listed for removal (specificity required in identification).","Cross-references to external documents (manufacturer service notice and FAA AD) for inspection technique and context."],"plain_english_summary":"**What this instrument does (mechanically):**\n\n- It requires operators of certain McDonnell Douglas (Hughes) and Kawasaki Model 369-series helicopters to check the serial number (S/N) of the main transmission output drive gear (part number 369D25127-11) within a short time window and to replace the gear if its serial number falls within two specified faulty batches. (Requirement 1; Compliance 1–2.)\n\n**Which aircraft are affected:**\n\n- All Model 369D, E, F, FF, 500N, AH-6 and MH-6 helicopters that have main rotor transmission P/N 369D25100 installed. (Applicability.)\n\n**What operators must do and when:**\n\n- Inspect or confirm the gear S/N within the next 10 hours time in service (TIS) after the directive becomes effective. This can be done by checking maintenance records, contacting the manufacturer, or direct inspection through the open liquid level plug port (the directive refers to a manufacturer service notice for that inspection method). (Requirement 1; Compliance 1.)\n\n- If the gear S/N is within the listed faulty ranges, replace the gear with an airworthy gear whose S/N is not in those ranges. Replacement deadlines depend on the helicopter's use and recordkeeping:\n  - Helicopters with a cargo hook and a separate permanent log of external-load hours: replace within 25 hours TIS of external-load operation, or within 400 hours TIS for non-external-load operation, whichever comes first. (Compliance 2a.)\n  - Helicopters with a cargo hook but no separate permanent external-load log: replace within 25 hours TIS after the directive's effective date. Operators may instead begin a separate external-load log on the effective date and then follow the 2a timetable. (Compliance 2b.)\n  - Helicopters without a cargo hook: replace within 400 hours TIS after the directive's effective date. (Compliance 2c.)\n\n- Once the defective gear has been replaced as required, there are no further follow-on inspections or maintenance actions mandated by this directive. (Compliance 3.)\n\n**Why the directive exists (stated reason):**\n\n- The directive records several reports of spalled or fractured teeth on the output drive gear. The problem was attributed to a manufacturing quality-control defect affecting certain batches of gears; the serial-number ranges in the directive identify those batches. (Background.)\n\n**Who pays, who decides, and what behaviour changes:**\n\n- Who pays: aircraft owners/operators pay for the inspection, replacement parts, labour and any downtime. (Compliance 1–2.)\n- Who decides: the Civil Aviation Safety Authority (by issuing the airworthiness directive) mandates the action; owners/operators must comply. (Applicability; Requirements/Compliance.)\n- Behaviour changes required: inspect the gear S/N quickly; if it is in the affected batches, remove and replace it within the specified hours thresholds; start and keep a separate external-load log if electing that option to qualify for the extended replacement window. (Requirement 1; Compliance 2b.)\n\n**Implementation details and mechanics to be aware of:**\n\n- The S/N check can be performed via paperwork, manufacturer confirmation, or a direct physical inspection through the liquid level plug port (the manufacturer’s service info is referenced for that method). (Requirement 1.)\n- Replacement must result in an \"airworthy\" gear whose S/N is not in the faulty ranges. The directive also cross-references a related FAA AD and a manufacturer notice. (Requirement 2; Note.)\n\n**Costs, trade-offs and implementation risks to consider:**\n\n- Direct costs and time: replacement parts and maintenance labour, plus helicopter downtime. These costs fall on the operators and any maintenance facilities they engage. (Compliance 2.)\n- Supply risk: if many affected gears require replacement, availability of replacement gears and lead times could increase aircraft downtime. (Implied by the replacement requirement.)\n- Monitoring burden: operators without an existing separate external-load log must either accept the shorter 25-hour replacement window or start and reliably maintain a separate log to use the longer compliance window for external-load operations. (Compliance 2a–2b.)\n- Safety benefit: replacing gears from identified faulty manufacturing batches reduces the risk of gear tooth spalling or fracture and the associated in-flight transmission failure risk. (Background.)\n\n**References used by the directive (for inspection or context):**\n\n- Manufacturer service information (MDHS Service Information Notice DN-189/EN82/FN-69/NN-009 dated Jan 10, 1997) is referenced for the inspection method. (Requirement 1.)\n- The directive also notes an equivalent FAA airworthiness directive (FAA AD 97-15-08) for cross-reference. (Note.)"},"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-hu-369-93-main-transmission-gear-replacement","history":"/api/acts/ad-hu-369-93-main-transmission-gear-replacement/history","analysis":"/api/acts/ad-hu-369-93-main-transmission-gear-replacement/analysis","conflicts":"/api/acts/ad-hu-369-93-main-transmission-gear-replacement/conflicts","importantCases":"/api/acts/ad-hu-369-93-main-transmission-gear-replacement/important-cases","documents":"/api/acts/ad-hu-369-93-main-transmission-gear-replacement/documents"}}