{"id":"F2006B07435","name":"AD/TPE 331/26 Amdt 1 - Installation of Direct Drive Fuel Control","slug":"ad-tpe-331-26-amdt-1-installation-of-direct-drive-fuel-control","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":49722,"registerId":"commonwealth-F2006B07435-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/TPE 331/26 Amdt 1 - Installation of Direct Drive Fuel Control","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)  \nAlliedSignal (Garrett/AiResearch) Turbine Engines \\- TPE 331 Series\n\nAD/TPE 331/26\n\nAmdt 1\n\n  \nInstallation of Direct Drive Fuel Control 1/92\n\nApplicability: TSE 331-3 and TPE 331-1, \\-2, \\-3, \\-5 and \\-6 series engines as listed by model and part number in Garrett Service Bulletin TPE 331-72-0061 Revision 5.\n\nRequirement: Incorporate the modified engine fuel control drive train in the main reduction gearbox in accordance with FAA AD 78-25-08 Revision 3 Amdt 39-3787. (Garrett SB TPE 331-72-0061 Revision 5 refers).\n\nNote: Equipment modified in accordance with previous issues of this Directive, or with AD/AIR-T/35 Amdt 3, do not require further rework.\n\nCompliance: The compliance date of the original issue of this Directive was 31 December 1985.\n\nThis re-issue is effective from 12 January 1992.\n\nBackground: This Directive was originally issued for the purpose of increasing N2 overspeed protection by the incorporation of SB 72-0061 and 72-0232 as a result of FCU drive problems experienced in Australia. Amendment 1 has the effect of aligning the Authority requirements with that of the FAA by removing the mandatory requirement to fit a modified torque sensor.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":true,"description":"The original directive required both a modified fuel control drive train AND a modified torque sensor. Amendment 1 narrows the scope by removing the torque sensor requirement, reducing the regulatory burden to align with FAA standards. This represents a contraction of scope rather than expansion."},"complexity_factors":["Single, specific technical requirement referencing external technical documents (FAA AD and Garrett Service Bulletin)","Limited applicability — only affects specific engine models listed in a service bulletin","Simple compliance structure with a fixed effective date and historical context","Contains one exemption clause (for previously modified equipment)","No nested definitions, conditional logic, or cross-references to other legislation beyond the cited FAA directive and service bulletin"],"plain_english_summary":"This Airworthiness Directive requires operators of certain AlliedSignal (Garrett/AiResearch) TPE331 turboprop engines to fit a modified fuel control gearbox connection (a \"direct drive\" FCU) to prevent FCU drive failures that can cause N2 overspeed. It affects aircraft using the listed TPE331 series engines (common on small turboprops). Amendment 1 drops the earlier torque-sensor mandate, aligns with FAA practice, and exempts engines already modified under prior versions."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"Yes. The amendment narrows the Directive's scope by removing the previously mandatory requirement to install a modified torque sensor, aligning the Authority's requirement with FAA AD 78-25-08 Revision 3 (Background). The primary retained mandate is incorporation of the modified fuel-control drive train per Garrett SB TPE 331-72-0061 Revision 5 (Requirement). Equipment already modified under earlier Directive issues or AD/AIR-T/35 Amdt 3 remain exempt (Note), so the practical set of required actions is reduced compared with the original issue."},"complexity_factors":["Cross-references to external technical instruments: the directive requires work \"in accordance with FAA AD 78-25-08 Revision 3\" and Garrett SB TPE 331-72-0061 Revision 5 (Requirement). This shifts detailed procedural content to other documents.","Applicability scope: applies to multiple specific engine models listed in the Garrett service bulletin (Applicability). Identifying affected engines requires consulting the SB's model and part-number lists.","Compliance and timing: the original compliance date is historical (31 December 1985) and the re-issue is effective 12 January 1992 (Compliance). Retrospective compliance tracking and maintenance records are relevant for enforcement.","Exemptions and prior work: equipment modified under earlier issues of this Directive or AD/AIR-T/35 Amdt 3 is explicitly exempt from further rework (Note). This creates an administrative need to verify modification history.","Amendment narrows technical mandate: Amendment 1 removes the mandatory fitment of a modified torque sensor to align with the FAA (Background). That changes the set of required physical interventions.","Operational/implementation burden: the mandated gearbox/drive-train modification is technical and will fall to certificated maintenance organisations; costs and aircraft downtime are borne by operators (Requirement).","Enforcement reliance: the Directive references FAA and manufacturer documents rather than reproducing full instructions, increasing reliance on cross-checking and interpretation of those documents (Requirement)."],"plain_english_summary":"This airworthiness directive requires operators of specified AlliedSignal (Garrett/AiResearch) TPE/TSE 331-series turboprop engines to install a modified engine fuel-control drive train in the main reduction gearbox by following Garrett Service Bulletin TPE 331-72-0061 Revision 5 (as adopted from FAA AD 78-25-08 Revision 3). It affects aircraft owners and maintenance organisations who must fund and schedule the retrofit to address fuel-control-unit drive problems and increase N2 overspeed protection. Amendment 1 removes the earlier mandatory requirement to fit a modified torque sensor."}},"importantCases":[],"_links":{"self":"/api/acts/ad-tpe-331-26-amdt-1-installation-of-direct-drive-fuel-control","history":"/api/acts/ad-tpe-331-26-amdt-1-installation-of-direct-drive-fuel-control/history","analysis":"/api/acts/ad-tpe-331-26-amdt-1-installation-of-direct-drive-fuel-control/analysis","conflicts":"/api/acts/ad-tpe-331-26-amdt-1-installation-of-direct-drive-fuel-control/conflicts","importantCases":"/api/acts/ad-tpe-331-26-amdt-1-installation-of-direct-drive-fuel-control/important-cases","documents":"/api/acts/ad-tpe-331-26-amdt-1-installation-of-direct-drive-fuel-control/documents"}}