{"id":"F2006B11018","name":"AD/JT9D/25 - Fan Blade Inspection/Revised Shroud Angle","slug":"ad-jt9d-25-fan-blade-inspection-revised-shroud-angle","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":56621,"registerId":"commonwealth-F2006B11018-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/JT9D/25 - Fan Blade Inspection/Revised Shroud Angle","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)  \nPratt and Whitney Turbine Engines \\- JT9D Series\n\nAD/JT9D/25 Fan Blade Inspection/Revised Shroud Angle 8/94\n\nApplicability: All JT9D-7R4 Series engines.\n\nRequirement: 1. Inspect fan blade leading edges in accordance with Pratt and Whitney Service Bulletin 72-255 Revision 5.\n\n2. Incorporate fan blades featuring a revised shroud angle in accordance with Pratt and Whitney Service Bulletin 72-309 Revision 10.\n\nIncorporation of Pratt and Whitney Service Bulletin 72-309 Rev 10 constitutes terminating action for the repetitive inspection per Requirement 1.\n\nNote: FAA AD 94-08-06 also refers.\n\nCompliance: 1. Initially within 200 cycles in service from 21 July 1994, and thereafter, at intervals not to exceed 200 cycles.\n\n2. No later than 21 July 1996.\n\nBackground: This Directive is issued to prevent fan blade failures that have been attributed to a combination of high vibratory stresses and foreign object damage.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The instrument applies specifically to all Pratt & Whitney JT9D-7R4 series engines and imposes inspection and modification requirements for those engines (Applicability; Requirement 1; Requirement 2). The text supplied does not indicate any expansion or narrowing of that applicability beyond the stated engine series, and it sets technical and timing requirements rather than altering the population covered."},"complexity_factors":["Narrow technical applicability limited to one engine series (JT9D-7R4) (Applicability)","Two discrete obligations: repeat inspections (with defined interval) and a retrofit/modification (Requirement 1; Requirement 2)","Simple, fixed compliance schedule with clear deadlines (Compliance 1; Compliance 2)","Dependence on external service bulletins for technical procedures and parts specifications (Requirement 1; Requirement 2)","Operational and supply-chain elements (availability of revised blades, scheduling aircraft downtime) increase practical complexity despite legal simplicity"],"plain_english_summary":"What this instrument does (mechanically):\n\n- It requires operators of Pratt & Whitney JT9D-7R4 series turbine engines to carry out a recurring inspection of the fan blade leading edges (Requirement 1) and to install fan blades that have a revised shroud angle (Requirement 2). The inspection procedure and the revised blades are specified by Pratt & Whitney Service Bulletins 72-255 Rev 5 and 72-309 Rev 10 respectively (Requirement 1; Requirement 2).\n- If an operator installs the revised shroud-angle fan blades in accordance with Service Bulletin 72-309 Rev 10, the repetitive inspection requirement stops (Requirement 2).\n- The inspection must start within 200 cycles in service from 21 July 1994 and be repeated at no more than 200-cycle intervals (Compliance 1). The revised blades must be incorporated no later than 21 July 1996 (Compliance 2).\n\nWho is affected:\n\n- Owners and operators of aircraft fitted with Pratt & Whitney JT9D-7R4 series engines (Applicability). They are the parties responsible for performing the inspections and for installing the revised blades (Requirement 1; Requirement 2; Compliance 1; Compliance 2).\n\nWhy it matters (stated purpose and mechanical test of that purpose):\n\n- The directive states its purpose is to prevent fan blade failures that have been attributed to a combination of high vibratory stresses and foreign object damage (Background).\n- Mechanically, the directive aims to reduce the risk of blade failure by (a) finding and monitoring damage through recurring inspections of blade leading edges (Requirement 1; Compliance 1) and (b) removing the need for continuing inspections by fitting blades with a revised shroud angle (Requirement 2; Compliance 2).\n\nCosts, incentives and trade-offs (how the instrument changes behaviour and who pays):\n\n- Direct compliance costs fall on engine/aircraft operators and owners, who must: perform the required inspections at the prescribed interval (every 200 cycles) and, within the stated deadline, procure and install the revised-shroud fan blades (Requirement 1; Requirement 2; Compliance 1; Compliance 2). These actions impose labour, parts and aircraft downtime costs.\n- Operators have an incentive to install the revised blades because doing so stops the need for the repetitive inspections (Requirement 2). That creates a trade-off between recurring inspection costs and a one-time modification cost.\n- The directive fixes the timing of required actions (initial inspection window and a latest date for modification), so operators must plan maintenance and parts procurement to meet those dates (Compliance 1; Compliance 2).\n\nImplementation risk and compliance burden:\n\n- Compliance requires following the specified Pratt & Whitney service bulletins (Requirement 1; Requirement 2). If revised blades are not immediately available, operators face scheduling and supply risk when meeting the no-later-than date for modification (Compliance 2).\n- The inspection cadence (every 200 cycles) is an operational burden that affects maintenance planning and aircraft availability (Compliance 1).\n\nBureaucratic discretion and enforceability:\n\n- The directive sets mandatory technical requirements and fixed compliance dates; it does not provide discretionary waivers or alternative compliance measures within the text supplied. Compliance is governed by the stated requirements and dates (Requirement 1; Requirement 2; Compliance 1; Compliance 2).\n\nEffects on private enterprise, competition and operational choice:\n\n- The measure reallocates costs to operators of the specified engine type; operators that can spread the modification cost across more flying hours may obtain lower per-hour cost compared with operators who continue inspections for longer before modifying.\n- The requirement affects any third parties that supply parts and maintenance services for JT9D-7R4 engines: demand for revised blades and inspection services will increase during the compliance window (Requirement 1; Requirement 2; Compliance 2).\n\nConcentrated benefits and diffuse costs (mechanisms, not value judgments):\n\n- The stated benefit (reduced risk of fan blade failure) accrues primarily to the operator, their passengers, and aircraft manufacturers/lessors by lowering failure risk (Background).\n- The costs (inspection labour, parts, downtime) are concentrated on operators of the specified engine series because the applicability is limited to JT9D-7R4 engines (Applicability).\n\nSource references from the instrument: Applicability; Requirement 1; Requirement 2; Compliance 1; Compliance 2; Background. Note: the instrument also cross-references an FAA airworthiness directive (Note)."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive with a narrow, specific scope (one engine series, one safety issue). It has not expanded beyond its original purpose of addressing fan blade failure risks through inspection and hardware modification."},"complexity_factors":["Very short document (under 200 words)","Only 2 substantive requirements with clear deadlines","Single defined applicability (one engine series)","No nested exceptions or conditional logic","Cross-reference to only one external FAA directive for context","Terminating action clearly specified (upgrade removes inspection obligation)"],"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 aircraft engines.\n\n**What it does:**\nThis directive applies to **Pratt & Whitney JT9D-7R4 series jet engines** (commonly used on Boeing 747 aircraft). It mandates two safety measures to prevent dangerous fan blade failures:\n\n1. **Repetitive inspections** — Engine operators must check the leading edges of fan blades for damage every 200 flight cycles (roughly 200 takeoff-landing trips), starting within 200 cycles of July 21, 1994.\n\n2. **Permanent hardware upgrade** — By July 21, 1996, operators must install redesigned fan blades with a \"revised shroud angle\" (a modified structural feature that helps blades withstand stress). Once this upgrade is done, the repetitive inspections are no longer required.\n\n**Why it matters:**\nFan blade failures can cause catastrophic engine damage and potentially endanger the aircraft. This directive addresses a known problem where blades were cracking due to a combination of vibration stress and damage from foreign objects (like birds or debris on runways).\n\n**Who it affects:**\nAirlines and aircraft operators flying planes with these specific Pratt & Whitney engines — primarily older Boeing 747 models."}},"importantCases":[],"_links":{"self":"/api/acts/ad-jt9d-25-fan-blade-inspection-revised-shroud-angle","history":"/api/acts/ad-jt9d-25-fan-blade-inspection-revised-shroud-angle/history","analysis":"/api/acts/ad-jt9d-25-fan-blade-inspection-revised-shroud-angle/analysis","conflicts":"/api/acts/ad-jt9d-25-fan-blade-inspection-revised-shroud-angle/conflicts","importantCases":"/api/acts/ad-jt9d-25-fan-blade-inspection-revised-shroud-angle/important-cases","documents":"/api/acts/ad-jt9d-25-fan-blade-inspection-revised-shroud-angle/documents"}}