{"id":"F2006B10755","name":"AD/HU 369/90 - Tail Rotor Blade Abrasion Strip","slug":"ad-hu-369-90-tail-rotor-blade-abrasion-strip","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":56203,"registerId":"commonwealth-F2006B10755-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/HU 369/90 - Tail Rotor Blade Abrasion Strip","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 369/90 Tail Rotor Blade Abrasion Strip 5/95\n\nDM\n\nApplicability: Model 369 series helicopters, with tail rotor blade assembly part numbers listed in McDonnell Douglas Helicopter Systems SIN HN-238, DN-187, EN-80, or FN-66.\n\nRequirement: 1\\. Inspect the tail rotor blade abrasion strip for debonding from the tail rotor blade. Prior to conducting the inspections, remove any abrasion tape from the tail rotor blade.\n\nIf the inspection reveals debonding, replace the tail rotor blade with an airworthy blade that has been modified by installation of rivets, and install 304 stainless steel abrasion tape (.0027 inch thick) over the inboard end of the abrasion strip in accordance with steps B through H of Part I of the Accomplishment Instructions of McDonnell Douglas SIN HN-238, DN-187, EN-80, or FN-66.\n\nIf the inspection reveals no debonding, install 304 stainless steel abrasion tape (.0027 inch thick) over the inboard end of the abrasion strip in accordance with steps B through H of Part I of the Accomplishment Instructions of McDonnell Douglas Helicopter Systems SIN HN-238, DN-187, EN-80, or FN-66.\n\n2. Replace the affected tail rotor blades in shipsets with tail rotor blades that contain the new-design abrasion strips in accordance with Part II of the Accomplishment Instructions of SIN HN-238, DN-187, EN-80, or FN-66. Once the new-design abrasion strips are installed on the tail rotor blades, the tail rotor assembly part number changes as follows:\n\nOld Tail Rotor Assembly No New Tail Rotor Assembly No 369A1613-7 369A1613-11\n\n369A1613-503 369A1613-507\n\n369A1613-505 369A1613-507\n\n369A1613-509 369A1613-507\n\n369D21606 369D21606-511\n\n369D21606-509 369D21606-511\n\n369D21613-11 369D21613-11N\n\n369D21613-31 369D21613-31N\n\n369D21613-41 369D21613-61\n\n369D21613-51 369D21613-61\n\n369D21613-71 369D21613-61\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n369D21615 369D21615-N\n\n369D21615-21 369D21615-31\n\n369D21615-41 369D21615-31\n\n421-088 421-088-11\n\nNote: FAA AD 95-03-11 Amdt 39-9147 refers.\n\nCompliance: 1. Unless already accomplished, within 25 hours time in service after 15 March 1995 or prior to 15 June 1995, whichever occurs first, and thereafter at intervals not to exceed 100 hours time in service; until Requirement 2 of this Directive is accomplished.\n\n2. Within 1,000 hours time in service after 15 March 1995.\n\nBackground: The FAA received several reports of incidents where tail rotor blade riveted abrasion strips debonded and separated during flight, which resulted in a severe out-of-balance condition and subsequent separation of the tail rotor gearbox from the helicopter.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"This AD stays within the original safety purpose: to eliminate the failure mode of abrasion strip debonding on specified Model 369 tail rotor blades. It combines interim mitigations (inspection and stainless tape) with a required permanent modification (replacement with new‑design abrasion strips). The directive did not expand into unrelated systems or add new regulatory objectives; it simply prescribes both short‑term and long‑term corrective actions to address the reported defect."},"complexity_factors":["Narrow subject matter: single component (tail rotor blade abrasion strip) and a limited set of models","Conditional logic: inspection → either replace (if debonding) or install stainless tape (if no debonding), then eventual mandatory replacement","Multiple compliance time conditions: initial window (25 hours or specific date, whichever first), recurring interval (≤100 hours) until permanent fix, and a 1,000 hour deadline for permanent replacement","Cross‑reference to multiple manufacturer's Service Instruction Numbers (HN‑238, DN‑187, EN‑80, FN‑66) and to specific steps (Part I steps B–H; Part II)","List of many specific old and new tail rotor assembly part numbers to track affected shipsets","Reference to a related FAA AD (95‑03‑11) for context"],"plain_english_summary":"**What this directive does (mechanical change)\n\n- Requires operators of McDonnell Douglas (Hughes) and Kawasaki Model 369 series helicopters that use certain tail rotor blade part numbers to inspect and, in many cases, modify or replace the tail rotor blade abrasion strip (the protective wear strip on the tail rotor blade).\n\n- Short‑term: Operators must remove any adhesive abrasion tape, inspect the abrasion strip for delamination or debonding (separation), and then install a 0.0027 inch thick 304 stainless steel abrasion tape over the inboard end of the abrasion strip. If any debonding is found, the affected blade must be replaced with a blade that has been modified by the installation of rivets before the stainless tape is fitted (Requirement 1; see Compliance timings).\n\n- Long‑term: The entire set of affected tail rotor blades must be replaced with blades fitted with the new‑design abrasion strips (a permanent modification) in accordance with the manufacturer's Accomplishment Instructions (Part II). Once blades are modified/replaced, the tail rotor assembly part number changes to a new number listed in the AD (Requirement 2).\n\n- The directive requires following specific steps (steps B–H of Part I and Part II) from the McDonnell Douglas Helicopter Systems Service Instruction Numbers (SIN) HN-238, DN-187, EN-80, or FN-66 for the detailed work.\n\n**Who must act and who pays\n\n- Who decides/acts: The helicopter operator and their maintenance provider must carry out the inspections and modifications. The Civil Aviation Safety Authority (via this Airworthiness Directive) mandates compliance.\n\n- Who pays: The operator bears the direct costs — labour for repeated inspections, the stainless steel tape installation, and eventual replacement of blades or entire blade shipsets. Maintenance shops will carry out the work and charge for parts and labour.\n\n**When the work must be done (timing and recurrence)\n\n- Interim inspections: Within 25 flight hours after 15 March 1995 or before 15 June 1995 (whichever comes first), unless already done; then repeat inspections at intervals not to exceed 100 flight hours until the permanent replacement is installed (Compliance, Requirement 1).\n\n- Permanent replacement: All affected blades must be replaced with the new‑design abrasion strip within 1,000 flight hours after 15 March 1995 (Requirement 2).\n\n**Why the regulator issued this AD (stated reason)\n\n- The FAA reported multiple incidents in which riveted tail rotor blade abrasion strips debonded and separated during flight. Those events caused severe out‑of‑balance conditions and led to at least one case where the tail rotor gearbox separated from the helicopter. The AD aims to prevent similar failures by requiring inspection, temporary reinforcement (stainless tape), and eventual install of a new‑design abrasion strip (Background).\n\n**Practical effects, trade‑offs and implementation notes (analyst's view)\n\n- Direct safety mechanism: The AD reduces the short‑term risk of abrasion strip separation by (a) detecting debonding early through inspections and (b) adding stainless steel tape at the inboard end as an interim reinforcement (Requirement 1). The permanent measure (Requirement 2) replaces blades with a design intended to remove the failure mode.\n\n- Costs and incentives: Operators incur recurring inspection costs (every ≤100 flight hours until replacement), one‑off costs to install stainless tape, and a larger cost to buy/fit new blades or shipsets. Operators face a clear financial incentive to schedule the permanent replacement within the 1,000‑hour window to avoid continued inspection burden.\n\n- Implementation risks and dependencies: Compliance requires access to the McDonnell Douglas Accomplishment Instructions (SIN HN‑238, DN‑187, EN‑80, FN‑66). Parts availability (stainless tape, riveted/modified blades or new‑design blades) will determine how quickly operators can complete the permanent replacement. Maintenance facilities must follow the referenced steps precisely; incomplete adherence risks ineffective mitigation.\n\n- Behavioural change: Maintenance regimes must add a new recurrent inspection task and plan for eventual blade replacement. Operators may reassign flying hours or delay non‑critical flights to meet compliance windows if parts or maintenance capacity are limited.\n\n- Concentrated benefits and diffuse costs: The safety benefit accrues to aircraft occupants and people on the ground (diffuse), while the cost burden is concentrated on individual operators who own and maintain the affected helicopters.\n\n- Cross‑references and compliance clarity: The AD depends on the manufacturer's service instructions for exact procedures and lists specific old and new tail rotor assembly part numbers to track which assemblies are considered modified (Requirement 2). It also notes the related FAA AD for additional context.\n\n**Key statutory/AD references used in this directive**\n- Requirement 1 (inspection, temporary reinforcement or replacement if debonding found)\n- Requirement 2 (mandatory replacement with new‑design abrasion strips; part‑number changes)\n- Compliance (timing: initial inspection window, recurring inspection interval, 1,000‑hour replacement deadline)\n- Background (FAA incident reports prompting the AD)\n\n(For technical execution, the AD requires following steps B–H of Part I and Part II of McDonnell Douglas SIN HN‑238, DN‑187, EN‑80, or FN‑66.)"},"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":3,"scope_assessment":{"changed":false,"description":"This is a standard airworthiness directive maintaining its original safety purpose. The scope remains tightly focused on the specific tail rotor blade defect in the 369 helicopter series."},"complexity_factors":["Multiple cross-references to manufacturer service bulletins (SIN HN-238, DN-187, EN-80, FN-66) without reproducing their content","Conditional logic: different actions required depending on inspection results (debonding found vs. not found)","Two-phase compliance structure: interim inspections with recurring intervals, plus ultimate replacement requirement","Detailed part number conversion table with 13 old-to-new part number mappings","Technical aviation terminology requiring specialized knowledge (time in service, shipsets, debonding, airworthiness)","Dual deadline calculation (25 hours after date OR before fixed date, whichever first)"],"plain_english_summary":"This FAA safety directive orders urgent inspections and interim repairs for certain McDonnell Douglas (Hughes) and Kawasaki Model 369 tail rotor blades after reports that abrasion strips can debond in flight, causing severe vibration and tail‑rotor gearbox separation. Affected operators must inspect blades, apply protective tape and install rivet‑secured strip replacements when needed, and complete a permanent blade redesign replacement (within the directive’s compliance timeline) to eliminate the hazard."}},"importantCases":[],"_links":{"self":"/api/acts/ad-hu-369-90-tail-rotor-blade-abrasion-strip","history":"/api/acts/ad-hu-369-90-tail-rotor-blade-abrasion-strip/history","analysis":"/api/acts/ad-hu-369-90-tail-rotor-blade-abrasion-strip/analysis","conflicts":"/api/acts/ad-hu-369-90-tail-rotor-blade-abrasion-strip/conflicts","importantCases":"/api/acts/ad-hu-369-90-tail-rotor-blade-abrasion-strip/important-cases","documents":"/api/acts/ad-hu-369-90-tail-rotor-blade-abrasion-strip/documents"}}