{"id":"F2006B11020","name":"AD/JT9D/27 - Fan Exit Case Cover Modification","slug":"ad-jt9d-27-fan-exit-case-cover-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":56625,"registerId":"commonwealth-F2006B11020-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/JT9D/27 - Fan Exit Case Cover Modification","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/27 Fan Exit Case Cover Modification 5/95\n\nApplicability: All JT9D-7R4 Series engines.\n\nRequirement: Modify the existing Fan Exit Case Cover assembly to incorporate a rubber bumper per Pratt and Whitney Service Bulletin JT9D-7R4-72-410.\n\nCompliance: At the first shop visit after 27 April 1995 but no later than 31 December 1995. Background: A Boeing 747 aircraft experienced an in-flight engine shut down due to loss of oil.\n\nSubsequent investigation identified loss of retention of the angle gearbox tower shaft cover as the cause of failure. In this instance failure of a threaded insert allowed the angle gearbox cover to migrate from its location recess resulting in a substantial oil leak.\n\nThe modification introduces a rubber bumper to the fan exit case access panel that abuts the angle gearbox tower shaft cover to prevent migration of the cover in the event that a cover bolt/insert fails.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"The directive imposes a new mandatory maintenance requirement on all JT9D-7R4 series engines: to modify the Fan Exit Case Cover assembly to include a rubber bumper in accordance with Pratt and Whitney Service Bulletin JT9D-7R4-72-410, to be completed at the next shop visit after 27 April 1995 or by 31 December 1995 (Applicability; Requirement; Compliance). Before issuance of this directive, that Service Bulletin was not made a regulatorily enforceable requirement by this instrument; the AD therefore expands regulatory scope by converting the Service Bulletin action into a mandatory compliance obligation (Requirement; Compliance)."},"complexity_factors":["Narrow technical scope (single engine family and single modification)","Clear applicability language: \"All JT9D-7R4 Series engines\" (Applicability)","Definite compliance timeline (first shop visit after 27 April 1995 but no later than 31 December 1995) (Compliance)","Dependency on external document for technical details (Pratt and Whitney Service Bulletin JT9D-7R4-72-410) (Requirement)","No exemption, calculation, or conditional criteria in the directive text (simple mandatory action)","Operational scheduling constraint (must be done at next shop visit) introduces practical but not legal complexity"],"plain_english_summary":"What this instrument does (mechanically)\n\n- Requires a physical change to Pratt & Whitney JT9D-7R4 series engines: the existing Fan Exit Case Cover assembly must be modified to include a rubber bumper. The modification is to be carried out in accordance with Pratt and Whitney Service Bulletin JT9D-7R4-72-410 (Requirement).\n- The modification must be completed at the next engine \"shop visit\" after 27 April 1995, and no later than 31 December 1995 (Compliance).\n\nWho issued the requirement and who decides\n\n- The directive is part of the Commonwealth civil aviation airworthiness directives administered under the Civil Aviation Safety Authority (header). That authority has set the mandatory requirement and compliance dates.\n\nWho is affected and who pays\n\n- Applicability is stated as “All JT9D-7R4 Series engines” (Applicability). That makes the requirement binding on any owner/operator or maintenance organisation responsible for engines in that family. The directive itself does not state who pays, but the modification must be carried out by the party that brings the engine to shop visit and so that party will incur the cost of parts and labour necessary to implement the Service Bulletin (Requirement; Compliance).\n\nWhy the change was ordered (the stated safety rationale) and the mechanical logic\n\n- Background information describes a real event: a Boeing 747 experienced an in‑flight engine shutdown because of an oil loss. Investigators identified that a threaded insert failed, allowing the angle gearbox tower shaft cover to move from its recess, which created a substantial oil leak (Background).\n- The mandated modification adds a rubber bumper on the fan exit case access panel that abuts the angle gearbox tower shaft cover. If a cover bolt or insert fails, the bumper is intended to prevent the cover from migrating and thereby reduce the risk of a large oil leak and related engine shutdown (Requirement; Background).\n\nImplementation and compliance mechanics, trade-offs and practical effects\n\n- The directive makes the Service Bulletin modification mandatory rather than optional: it must be done at the next scheduled shop visit within the prescribed window (Requirement; Compliance). That turns a manufacturer service instruction into a regulatorily enforceable task for the applicable engines.\n- Compliance imposes a discrete maintenance task that will require parts and labour at the next shop visit (Requirement; Compliance). The timing requirement creates a scheduling constraint for operators and maintenance providers: the work may be deferred only until the next shop visit but in any event must be done by 31 December 1995 (Compliance).\n- Implementation depends on following the manufacturer’s Service Bulletin; therefore the detailed procedure and parts specification are under the manufacturer’s instruction (Requirement). This channels the technical execution to the Service Bulletin’s content rather than specifying the modification steps in the directive itself.\n\nCosts, incentives and risk trade-offs (mechanism-focused)\n\n- Cost imposition: the directive shifts the immediate cost of parts and installation onto whoever conducts the required shop visit (Requirement; Compliance). The directive does not allocate funding or compensation.\n- Incentives: by mandating the retrofit, the regulator increases the expected private cost of operating an affected engine until the modification is installed, creating an incentive to schedule the modification at the next available maintenance opportunity (Compliance).\n- Risk reduction mechanism: the rubber bumper changes the mechanical interaction between the fan exit case access panel and the angle gearbox tower shaft cover so that a single point failure of a bolt/insert is less likely to lead to cover migration and a consequent oil leak (Requirement; Background).\n- Implementation risk and administrative discretion: the directive relies on the Service Bulletin for technical details; enforcement of compliance and timing rests with the regulator and with normal maintenance oversight processes (Requirement; Compliance).\n\nNet operational effect (concise)\n\n- Operators of JT9D-7R4 engines must ensure the rubber bumper modification is fitted per the manufacturer’s Service Bulletin by the next shop visit after 27 April 1995 or by 31 December 1995 (Applicability; Requirement; Compliance). The measure converts a manufacturer-recommended change into a mandated maintenance action with a fixed compliance window and shifts the immediate cost and scheduling burden to those maintaining the engines."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific mechanical failure mode in a specific engine series. It has not expanded beyond its original purpose of mandating a manufacturer-recommended modification to prevent oil leaks from gearbox covers."},"complexity_factors":["Single, specific technical requirement (add rubber bumper per manufacturer bulletin)","Clear applicability (one engine series only)","Simple compliance deadline (first shop visit after date X, or hard deadline Y)","No defined terms section, no cross-references to other legislation beyond the enabling regulations","Straightforward factual background with single causal chain"],"plain_english_summary":"This is an **Airworthiness Directive** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for aircraft engines.\n\n**What it does:**\nIt requires owners and operators of **Pratt & Whitney JT9D-7R4 series jet engines** (commonly used on Boeing 747 aircraft) to modify a specific engine part called the **Fan Exit Case Cover**. The modification involves adding a **rubber bumper** to prevent a dangerous mechanical failure.\n\n**Why this matters:**\nA Boeing 747 had an engine failure in flight because a cover on the engine's angle gearbox came loose. This happened when a threaded insert (a metal fitting that holds bolts) failed, allowing the cover to move out of position and causing a major oil leak. The engine had to be shut down mid-flight.\n\nThe rubber bumper acts as a **physical backup** — even if the bolts or inserts fail again, the bumper stops the cover from moving and leaking oil.\n\n**Who must comply:**\nAnyone operating aircraft with these specific Pratt & Whitney engines.\n\n**When:**\nThe modification had to be done during the engine's first maintenance shop visit after 27 April 1995, but absolutely no later than 31 December 1995."}},"importantCases":[],"_links":{"self":"/api/acts/ad-jt9d-27-fan-exit-case-cover-modification","history":"/api/acts/ad-jt9d-27-fan-exit-case-cover-modification/history","analysis":"/api/acts/ad-jt9d-27-fan-exit-case-cover-modification/analysis","conflicts":"/api/acts/ad-jt9d-27-fan-exit-case-cover-modification/conflicts","importantCases":"/api/acts/ad-jt9d-27-fan-exit-case-cover-modification/important-cases","documents":"/api/acts/ad-jt9d-27-fan-exit-case-cover-modification/documents"}}