{"id":"F2006B10745","name":"AD/HU 369/80 - Bolts in Main Transmission","slug":"ad-hu-369-80-bolts-in-main-transmission","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":116751,"registerId":"commonwealth-F2006B10745-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/HU 369/80 - Bolts in Main Transmission","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 369/80 Bolts in Main Transmission 7/90\n\nApplicability: 1. All Model 369D, 369E serial numbers 0001E through 0352E and 369F/FF serial number 0001F through 0067FF series helicopters.\n\n2. All spare MS21250-04036 bolts purchased from MDHC or directly from Air Industries since August 1988. Any spare transmission delivered prior to September 1989.\n\nRequirement: Action in accordance with McDonnell Douglas SIN DN-166, EN-57 or FN-45, as applicable.\n\nCompliance: For Helicopters: Unless previously carried out, within 300 hours time in service from 12 July 1990 or by 30 April 1991, whichever occurs first.\n\nFor Spares: Before installation on a helicopter after 30 May 1991.\n\nBackground: The manufacturer has advised that certain bolts may not meet industry standards.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive’s scope is limited to the specific helicopter serial ranges and the defined spare-bolt population identified in the text. That scope matches the stated purpose in the Background (to address certain bolts that may not meet industry standards) and is implemented by mandating actions in the manufacturer’s service instructions (Applicability; Background; Requirement)."},"complexity_factors":["Narrow applicability limited to specific models and serial number ranges (Applicability: 1).","Inclusion of a specific spare part number and supplier/time window for spares (MS21250-04036; Applicability: 2).","External technical detail is delegated to manufacturer service instruction notices (SIN DN-166, EN-57, FN-45), which are not reproduced in the directive (Requirement).","Two different compliance regimes: a flight-hours/calendar deadline for in-service helicopters and a calendar cutoff for spares (Compliance).","Potential operational scheduling and parts-availability impacts during the prescribed compliance window (Compliance)."],"plain_english_summary":"### What this directive does (mechanical effect)\n\nThis airworthiness directive applies to certain McDonnell Douglas (Hughes) and Kawasaki 369 series helicopters and to some spare bolts (MS21250-04036). It requires operators to carry out the actions specified in the manufacturer’s service instruction notices (McDonnell Douglas SIN DN-166, EN-57 or FN-45) for those helicopters and spares (Requirement). For aircraft already in service the work must be done within 300 hours time in service from 12 July 1990 or by 30 April 1991, whichever comes first. For affected spare bolts, the directive bars installation on a helicopter after 30 May 1991 unless the required action has been done (Compliance; Applicability).\n\n### Who is covered\n\n- All Model 369D, 369E with serial numbers 0001E–0352E and all 369F/FF with serial numbers 0001F–0067FF (Applicability: 1).\n- Spare bolts part number MS21250-04036 that were purchased from MDHC or directly from Air Industries since August 1988, and any spare transmission delivered prior to September 1989 (Applicability: 2).\n\n### Why it was issued (official rationale)\n\nThe manufacturer advised that certain bolts may not meet industry standards (Background). The directive implements the manufacturer’s remedial instructions to address that concern (Requirement).\n\n### Who pays, who decides, and what changes in behaviour\n\n- Who pays: Owners/operators of the affected helicopters and holders/installers of the affected spare bolts must carry out the work or replacement called for by the manufacturer’s service instructions. That includes labour, parts and aircraft downtime (Requirement; Compliance).\n- Who decides: The Civil Aviation Safety Authority issued this Schedule of Airworthiness Directives and enforces compliance; the actual technical steps are those set out by the manufacturer in SIN DN-166, EN-57 or FN-45 (header; Requirement).\n- Behaviour changes: Operators must inspect/modify/replace bolts in the specified aircraft within the stated time window; parts suppliers and maintenance organisations must ensure affected spare bolts are not fitted after 30 May 1991 unless they have been treated per the instructions (Compliance; Applicability).\n\n### Implementation, costs and practical trade-offs\n\n- Compliance requires following external manufacturer documents rather than steps spelled out in the directive itself, so maintenance providers must obtain and follow SIN DN-166, EN-57 or FN-45 to know the exact technical work (Requirement).\n- There is an operational cost: affected helicopters may be grounded or taken out of service while the work is done, and owners bear the direct costs of parts and labour (Compliance).\n- The directive targets a discrete set of serial numbers and a specific bolt part number, concentrating costs on a subset of operators and spare-holders, while the safety benefit (as stated by the manufacturer) is broader but applied only to the listed items (Applicability; Background).\n- Timing constraints create an implementation risk where maintenance slots, parts availability or access to the required service instructions could delay compliance; the AD gives both an hours-based and a calendar deadline for in-service helicopters, and a calendar cutoff for spares (Compliance).\n\n### Practical notes on interpretation\n\n- The AD makes compliance conditional on ‘‘action in accordance with McDonnell Douglas SIN DN-166, EN-57 or FN-45’’ rather than specifying procedures; therefore, the precise scope of required work depends on those documents (Requirement).\n- The directive explicitly identifies the affected bolt part number (MS21250-04036) and the source/time window for concerned spares (purchased from MDHC or Air Industries since August 1988) (Applicability: 2).\n\n(References: Applicability; Requirement; Compliance; Background.)"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific manufacturing defect in helicopter components. It has not expanded beyond its original purpose of ensuring bolt integrity in the main transmission of specific helicopter models."},"complexity_factors":["Single, specific mechanical issue (bolt quality)","Limited applicability to specific helicopter models and serial number ranges","Straightforward compliance timeline with clear deadlines","Only 3 defined applicability categories (helicopters, spare bolts, spare transmissions)","No nested exceptions or conditional logic — compliance is mandatory with simple alternative deadlines","References external technical documents but does not reproduce them","Total length: approximately 150 words"],"plain_english_summary":"This is an **Airworthiness Directive** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) that requires specific maintenance actions on certain helicopters.\n\n**What it does:**\nOrders owners and operators of specific McDonnell Douglas (Hughes) and Kawasaki 369 series helicopters to inspect or replace certain bolts in the main transmission (the gearbox that transfers power from the engine to the rotor blades).\n\n**Who it affects:**\n- **Helicopter models:** Model 369D, 369E (serial numbers 0001E to 0352E), and 369F/FF (serial numbers 0001F to 0067FF)\n- **Spare parts:** Specific bolts (MS21250-04036) bought from the manufacturer or Air Industries since August 1988, plus any spare transmissions delivered before September 1989\n\n**What must be done:**\nFollow the manufacturer's service instructions (referenced as SIN DN-166, EN-57, or FN-45 depending on the specific helicopter model).\n\n**When it must be done:**\n- **For helicopters already in service:** Within 300 flight hours after 12 July 1990, or by 30 April 1991 — whichever comes first\n- **For spare parts:** Before installing them on any helicopter after 30 May 1991\n\n**Why it matters:**\nThe manufacturer discovered that certain bolts might not meet required strength standards. Since these bolts hold the main transmission together, a failure could cause catastrophic loss of the helicopter. This directive forces operators to fix the problem before a dangerous failure occurs."}},"importantCases":[],"_links":{"self":"/api/acts/ad-hu-369-80-bolts-in-main-transmission","history":"/api/acts/ad-hu-369-80-bolts-in-main-transmission/history","analysis":"/api/acts/ad-hu-369-80-bolts-in-main-transmission/analysis","conflicts":"/api/acts/ad-hu-369-80-bolts-in-main-transmission/conflicts","importantCases":"/api/acts/ad-hu-369-80-bolts-in-main-transmission/important-cases","documents":"/api/acts/ad-hu-369-80-bolts-in-main-transmission/documents"}}