AD/TFE 731/36 - Interstage Turbine Transition Duct

The AD is brief and built around a small set of interlocking concepts pulled from the text. Those concepts determine who must act and how compliance is judged.

• Applicability. The AD applies to Honeywell International Inc. TFE731-4, -4R, -5, -5AR, -5BR and -5R series turbofan engines when they have installed ITT duct part numbers listed in the applicability block. The AD notes that these engines are installed on, but not limited to, specific aeroplane models (examples include Dassault Falcon 50 series, Dassault 20/50/900/MF900 series, Cessna Model 650 and Citation VII, and Hawker 800/850XP series). The list of part numbers is the concrete locus of applicability.

• Affected component. The regulated item is the interstage turbine transition duct (ITT duct), identified by specific part numbers: 3075292-1, 3075292-3, 3074766-1, 3077063-1, 3075655-1, 3075655-2, 3075699-1, and 3075699-3 (as listed in the applicability text).

• Remedial action. The primary operational action required is replacement of any affected ITT duct with a “serviceable and redesigned” ITT duct. The AD contains an explicit definition: a serviceable and redesigned ITT duct is one not having a part number listed in this AD. That definition places the obligation on operators to ensure replacement parts do not carry any of the proscribed part numbers.

• Timing and triggers. Compliance is tied to maintenance events: the next Major Periodic Inspection of the engine or the next access of the ITT duct, whichever occurs first, but with an absolute limit of 2,600 hours time-in-service after the effective date of the AD. The AD defines “next access” as the event when the ITT duct is removed from the engine.

• Prohibition. After the effective date, the AD explicitly forbids installing any of the listed ITT duct part numbers onto any engine.

• Related technical guidance. The AD identifies Honeywell Service Bulletins TFE731-72-3727 and TFE731-72-3728 as pertaining to the subject matter, and it refers to FAA AD 2008-19-12 as related information. These documents are not reproduced in the AD but are cited as reference material that “pertain to the subject of this AD” or “refer” to the matter.

• Safety rationale. The AD is explicitly presented as a preventive measure in response to reported LPT blade separation events and documented instances where nozzle assembly failure and ITT duct deformation led to uncontainment.

Those concepts supply the compliance test: an engine with one of the listed ITT duct part numbers must have that duct replaced with a non-listed part by the stated inspection or access trigger, and no listed duct may be installed after the effective date.

The AD’s immediate legal and practical audience is the chain of parties who own, operate, maintain, or certify the affected engines and installed aeroplanes. From the text alone, the affected groups are:

• Aircraft operators and owners. Any operator or owner with Honeywell TFE731 engines fitted with ITT ducts that carry any of the listed part numbers is subject to the AD’s replacement and installation prohibition requirements. The applicability block expressly names engine series and lists example aeroplane types on which those engines are installed, and it also states the engines are installed on, but not limited to, the listed airframes. That wording implies owners of other types that have the listed engine and part numbers are also captured.

• Maintenance organisations, licensed engineers and overhaul facilities. The replacement requirement is activation at the next Major Periodic Inspection or next access of the ITT duct. The work will therefore fall to maintenance organisations or personnel performing those inspections or disassembling the engine to access the ITT duct. These organisations must ensure they do not re-fit proscribed part numbers, and must source a “serviceable and redesigned” ITT duct (the AD defines that by exclusion of part numbers listed in the AD).

• Logistics and parts suppliers. The installation prohibition applies to any ITT duct that carries one of the listed part numbers. Suppliers, stores and logistics managers holding stock of the listed P/Ns need to ensure those parts are not installed on engines after the AD’s effective date and must manage inventory accordingly. The AD’s text leaves the practical handling of existing stock to the operator and supplier, but the prohibition is explicit.

• Certifying and regulatory bodies. The Civil Aviation Safety Authority (CASA) issued the AD and set the effective date. The AD also references related guidance from the OEM (Honeywell) and the FAA, which means regulators, repair agencies and certifying engineers will use those documents to assess conformity with the AD’s requirements.

• Designers and Honeywell. Although the AD does not impose obligations on Honeywell directly, it cites Honeywell service bulletins as relevant. Honeywell will be the source of the “redesigned” ITT duct and likely the technical instructions for replacement; maintenance providers will rely on Honeywell documents to accomplish the AD-prescribed replacement.

Who pays. The text does not specify funding arrangements. The replacement and associated labour, downtime and parts costs fall to whoever is responsible for maintaining the engines under their operating certificate and maintenance programmes, commonly operators or lessors, and to maintenance organisations contracted to do the work.

Who decides. The AD fixes decision points: CASA issued the directive and determined effective date and requirements. Operationally the operator decides scheduling to meet the timing triggers, and maintenance providers decide technical execution referencing Honeywell service bulletins.

What changes for affected parties. Operators must schedule replacement work by the stated triggers, ensure any replacement ITT duct does not carry a listed part number, and ensure no listed P/N is installed after the effective date. Maintenance providers must perform the replacements in line with the triggers and ensure parts traceability to demonstrate compliance.

The AD sets out a compact compliance regime. The duties are concrete and narrowly defined in the AD; the document does not enumerate discretionary rights or appeal procedures. From the source text, the principal duties are:

• Identify affected hardware. Duty to determine whether engines in the operator’s fleet have installed ITT ducts with any of the part numbers listed in the applicability block. The AD lists those part numbers and the engine series to which the AD applies.

• Replace specified ITT ducts. Where an affected part is present, the operator must replace that ITT duct with a “serviceable and redesigned ITT duct,” meaning a duct without any of the listed part numbers, at the earlier of: the next Major Periodic Inspection of the engine or the next access of the ITT duct, but not later than 2,600 hours time-in-service after the AD’s effective date. This replacement duty is the core substantive obligation.

• Do not install proscribed parts. The operator, maintenance organisation and any agent must not install any ITT duct listed by part number in the AD onto any engine after the AD’s effective date. The AD frames this as Requirement 2 and makes it effective immediately after the effective date.

• Observe definitions supplied by the AD. The AD defines “serviceable and redesigned ITT duct” by exclusion, that is, as one not having a part number listed in the AD, and defines the trigger “next access” as when the ITT duct is removed from the engine. Compliance rests on correct application of those definitions.

• Use related technical guidance where relevant. While the AD does not make the Honeywell service bulletins mandatory text within the AD, it identifies Honeywell SB No. TFE731-72-3727 and SB No. TFE731-72-3728 (both dated 12 September 2007) as pertaining to the subject of the AD. Operators and maintainers will reasonably use those SBs to execute safe and approved replacement procedures; the AD’s “Related Information” section points to that guidance.

Rights and non-specified procedures. The AD text does not set out explicit rights of review, deferral, or alternative methods of compliance (AMOC) within the document. It likewise does not articulate record-keeping obligations or inspection certification steps. Those matters are normally handled under the broader regulatory framework and maintenance regulations, not by the AD itself. The AD does supply specific definitions and deadlines that limit scope for alternative compliance unless otherwise permitted by the regulator (not stated in the AD text).

Operational consequences of duties. The requirements will force timing and logistical choices: re-prioritise maintenance tasks to meet the “next Major Periodic Inspection or next access” trigger, source replacement ITT ducts that do not carry any of the listed part numbers, and ensure parts inventory is not used in contravention of the installation prohibition.

The AD text itself specifies the compliance actions and effective date (18 December 2008), but it does not state any monetary penalties, criminal sanctions or administrative fine schedule in the document. The directive form shows it was issued by the Civil Aviation Safety Authority (signed by James Coyne on 6 November 2008), which establishes the issuing authority, but the AD does not enumerate enforcement mechanisms, penalty amounts or enforcement procedures within the text provided.

What the AD does supply relevant to enforcement is the mandatory nature of the replacement and installation prohibition and the clear timeline for compliance: replacement by the earlier of the next Major Periodic Inspection or next access of the ITT duct, but no later than 2,600 hours time-in-service after the effective date, and an immediate ban on installing listed P/Ns after the effective date. Those specifics are the compliance benchmarks an enforcement agency would use to determine whether an operator has complied.

Because the AD does not set out enforcement penalties within its own wording the following points arise from the text and its regulatory form:

• The issuing body is the Civil Aviation Safety Authority, as represented by the signature block. That identification indicates which regulator is responsible for issuing the AD and therefore which body would normally be the point of compliance oversight.

• The AD establishes compliance metrics. The effectiveness of any enforcement or oversight action will depend on demonstrable evidence that the replacement was performed within the stated triggers and that no proscribed parts were installed after the effective date. Maintenance records, parts traceability and inspection logs are the natural documents for that showing, although the AD does not mandate textually how records must be kept.

• The AD does not describe an administrative process for departure from the requirement, such as an approved alternative method of compliance or relief for in-service constraints. The absence of such a provision in the AD text means the document does not itself authorise deviations; any alternate approval would have to come from the regulator under whatever procedures the regulator uses outside the AD text (not detailed in the AD).

If parties require clarity on enforcement mechanisms, penalty exposure or approval for alternatives, the AD’s reference to related material (Honeywell service bulletins and the FAA AD) does not supply that material; operators must consult CASA’s broader regulatory instruments or contact CASA directly for enforcement policy and possible relief mechanisms. The AD itself provides the substantive mandatory requirements and the effective date; it does not provide a penalty schedule or enforcement step-by-step rules in the text supplied.

The AD makes two explicit cross-references and otherwise stands as a regulatory instrument issued by the Civil Aviation Safety Authority. From the document text:

• Relationship to Honeywell service bulletins. The AD identifies Honeywell International Inc. Service Bulletin No. TFE731-72-3727 and SB No. TFE731-72-3728, both dated 12 September 2007, as “pertain[ing] to the subject of this AD.” That phrasing indicates the Honeywell SBs are technical documents relevant to the replacement and redesign procedures, but the AD does not itself incorporate those SBs by reference as mandatory text within the AD. Operators and maintainers will ordinarily use those SBs as the technical basis for executing the replacements required by the AD.

• Relationship to the FAA AD. The AD notes: “Note 2: FAA AD 2008-19-12 Amdt 39-15679 dated 12 September 2008 refers.” That cross-reference signals that a parallel regulatory action exists in the United States and that the CASA AD and the FAA AD address the same technical issue. The AD does not state whether or how any differences between the FAA AD and the CASA AD are to be reconciled; it simply records the FAA AD as related information.

• Interaction with broader regulatory framework. The AD is a Civil Aviation Safety Authority directive. The text does not reproduce or restate any general maintenance regulation, certification requirement, or penalty regime; it supplies a targeted mandatory instruction about specific hardware and replacement timing. In a typical regulatory system an AD sits within a broader legal framework of airworthiness regulations, maintenance rules and operator responsibilities. The AD text does not itself map those interactions, or cite specific regulatory provisions in the broader statutory scheme.

• Relationship to parts and design approvals. The AD defines “serviceable and redesigned ITT duct” as a duct not having a part number listed in the AD. The AD does not specify the approved part number(s) for the redesigned duct or whether additional design approval, supplemental type certificate, or parts authorisation is required to source and fit the replacement unit. Honeywell service bulletins are cited as related documentation, which suggests the redesigned parts and instructions will be found there. The AD text does not itself confirm any design approval process or special airworthiness acceptance criteria for the redesigned ducts.

• No express effect on contracts or warranties. The AD does not address contractual relationships, warranties or liabilities between operators, maintainers and Honeywell. Any such interactions will be governed by the parties’ contracts and by general legal rules outside the AD text.

In sum, the AD explicitly points to Honeywell SBs and the FAA AD as related material and otherwise operates as a focused regulatory instruction. The AD does not, in the text provided, create or explain interaction mechanisms with other laws, penalty provisions or alternative compliance procedures; those matters would be handled under the wider regulatory and legal framework beyond the printed AD.

The AD text supplied contains its issuance details and effective date but no later amendments, revisions or historical versions in the document supplied. The concrete data present are:

• Issuance signatory and date. The AD includes the signature block: James Coyne, Delegate of the Civil Aviation Safety Authority, dated 6 November 2008.

• Effective date. The AD states: “This Airworthiness Directive becomes effective on 18 December 2008.”

• Cross-references to other jurisdictions and documents. The AD cites FAA AD 2008-19-12 Amdt 39-15679 dated 12 September 2008 and Honeywell Service Bulletins dated 12 September 2007 as related information. Those citations document the contemporaneous technical and international regulatory context at the time of issuance.

The AD does not show any subsequent amendments or a history of prior versions within the text provided. It does not list earlier or later amendment numbers, superseded ADs, or revocations. There is no text in the supplied document indicating that the AD had been amended or superseded as of the effective date supplied. If users need an authoritative amendment history, they must consult the Civil Aviation Safety Authority’s records, the national regulatory AD register, or the relevant maintenance directives repository, as the AD text here contains no further amendment trace.

The AD text does not include any litigation history, references to judicial review, or records of legal challenges. The document is a regulatory measure issued by the Civil Aviation Safety Authority and signed by its delegate; it contains technical and compliance instructions and related citations, but it does not report any court proceedings, appeals, or decisions.

From the supplied text alone:

• No cases or legal proceedings are named or referenced.

• No administrative appeal routes or dispute mechanisms are set out in the AD text.

Because the AD is a technical compliance instrument and not a legislative history document, the absence of litigation references within it does not imply that litigation has never occurred; it only means no litigation history is recorded in the AD text supplied. For any search for judicial decisions or disputes that may have arisen from this AD, consult court records, administrative rulings, or CASA’s public records outside the text of this AD.

Practical traps and points of ambiguity that read directly from the AD text and that an operator, maintainer or parts supplier should note are as follows.

• Part number list is the compliance trigger and the prohibition anchor. The AD’s applicability block lists specific ITT duct part numbers. The compliance obligations depend entirely on whether an installed ITT duct carries one of those listed part numbers. Operators must verify the installed ITT duct part number rather than relying on engine model alone. The AD also refers to “paragraph (c)” for the P/N list in the installation prohibition; the P/Ns appear in the applicability section, so care is needed to match the AD’s internal references in your maintenance documentation.

• Definition by exclusion may create interpretation questions. The AD defines a “serviceable and redesigned ITT duct” as “one not having a part number listed in this AD.” That definition treats the set of acceptable parts as any part that does not use a proscribed part number. In practice this means an operator must be able to identify the part numbers of any candidate replacement to demonstrate compliance. The AD itself does not list the approved replacement part number(s) or provide positive identification guidance for the redesigned duct; operators should use Honeywell service bulletins or OEM records to identify the correct replacement part number and configuration.

• “Next access” is precisely defined but may be operationally ambiguous. The AD defines “next access” as when the ITT duct is removed from the engine. In some maintenance programmes the ITT duct may be removed only during planned overhauls or major inspections; operators should be careful when scheduling or deferring other maintenance activities that might constitute “access” and thereby trigger the replacement obligation.

• Timing cap and competing scheduling pressures. The replacement must occur at the next Major Periodic Inspection or next access, whichever occurs first, but not to exceed 2,600 hours time-in-service after the effective date. Operators with infrequent access to the ITT duct or with complex scheduling constraints must plan to avoid breaching the 2,600-hour cap. The AD sets a firm upper limit that is independent of routine inspection cycles.

• Prohibition is immediate after effective date. Requirement 2 states that after the effective date the listed part numbers must not be installed on any engine. That means that even if an operator has spares or stock of the proscribed P/Ns, those parts cannot be fitted after 18 December 2008. Inventory holders must ensure their stock management prevents prohibited installs.

• Use of related documents for technical execution. The AD cites Honeywell service bulletins as “pertain[ing] to the subject of this AD.” The AD does not itself contain detailed replacement instructions or illustrations; implementers must consult the referenced Honeywell SBs for the technical steps. Relying solely on the AD text without the OEM SB risks omission of assembly, torque, or inspection instructions that the SB provides.

• Applicability wording “installed on, but not limited to.” The AD lists several aeroplane types as examples. The phrase “installed on, but not limited to” indicates that the AD is not confined to those airframes; the core applicability depends on the engine and the installed ITT duct P/N, not on the example aircraft list. Do not exclude an airframe merely because it is not named.

• Cross-reference to FAA AD and international context. The AD notes related FAA AD 2008-19-12. This cross-reference can be helpful for operators managing transnational fleets, but domestic compliance obligations are governed by this CASA AD. If a fleet operator is subject to multiple authorities, ensure each authority’s ADs are complied with where applicable.

• No explicit acceptance of alternative methods in the text. The AD does not set out a process for alternative compliance. If an operator believes an alternative mitigation is equivalent, the AD text does not itself provide for approval; any alternative must be pursued through the regulator’s standard channels outside the AD text.

• Records and proof of compliance. The AD does not prescribe record-keeping steps. Operators should prepare to document part numbers, removal dates, and replacement parts to demonstrate compliance, because the AD sets clear temporal and part number conditions that enforcement or auditing authorities will verify.

Those “gotchas” are direct operational consequences of the AD’s wording and should guide maintenance planning, parts management and compliance documentation.

The AD contains concise mandatory steps. A practical compliance pathway, strictly drawn from the AD text and the referenced material, is as follows.

1. Inventory and identification. Immediately review fleet records to identify any TFE731-4, -4R, -5, -5AR, -5BR and -5R engines and determine whether the installed ITT duct carries any of the listed part numbers: 3075292-1, 3075292-3, 3074766-1, 3077063-1, 3075655-1, 3075655-2, 3075699-1, and 3075699-3. Record serial numbers, installation dates and any prior maintenance entries that document the current ITT duct part number.

2. Plan replacements according to AD triggers. For engines with proscribed ITT ducts, plan replacement at the earlier of:

   • The next Major Periodic Inspection of the engine; or
   • The next access of the ITT duct, which the AD defines as when the ITT duct is removed from the engine. Ensure that no replacement is deferred past 2,600 hours time-in-service after the AD’s effective date (18 December 2008). If either the next Major Periodic Inspection or the next access falls before that 2,600-hour cap, the earlier event is the operative trigger.

3. Procure compliant replacement parts. Obtain a “serviceable and redesigned ITT duct,” as the AD defines that term, namely an ITT duct not having any of the part numbers listed in the AD. The AD cites Honeywell service bulletins TFE731-72-3727 and TFE731-72-3728 (both dated 12 September 2007) as relating to the subject. Use the Honeywell SBs and OEM parts lists to identify the correct replacement part number and to confirm the redesigned configuration.

4. Execute replacement with technical conformity. Use Honeywell service bulletin instructions for removal, inspection and fitting as those SBs “pertain to the subject of this AD.” Follow approved maintenance procedures, torque values, inspection points and any post-installation tests specified in the OEM documentation. Ensure the replacement is recorded in maintenance logs with the new part number, date, and signatory certifying the work.

5. Do not install listed P/Ns after effective date. After 18 December 2008, do not install any ITT duct that has one of the listed part numbers onto any engine. That prohibition applies equally to spares and in-field repairs; ensure parts stores and maintenance planning systems block use of proscribed P/Ns.

6. Documentation and traceability. Although the AD does not prescribe record-keeping, prepare records that demonstrate compliance: evidence that an affected ITT duct was removed and replaced within the stated triggers, identification of the replacement part number, who performed the work, and associated maintenance entries. Records are the means by which compliance will be shown to the regulator in an audit or inspection.

7. Coordinate with parts suppliers and Honeywell. Engage parts suppliers and Honeywell to confirm availability and lead times of the redesigned ITT duct. Because the AD defines acceptable replacement by exclusion of proscribed P/Ns, confirm the replacement part number and ordering codes to avoid inadvertent procurement of proscribed items.

8. Address fleet planning. For operators with multiple aircraft, prioritise aircraft whose next Major Periodic Inspection or next access is imminent to ensure replacements occur by the required triggers. For engines not scheduled for near-term access, measure remaining time-in-service against the 2,600-hour cap and plan accordingly.

9. Seek regulator guidance if uncertain. If there are unresolved questions about whether a candidate replacement part meets the AD’s definition of “serviceable and redesigned ITT duct,” or if operational constraints make it impossible to meet the triggers, consult CASA or the appropriate regulatory authority for guidance on alternative methods of compliance. The AD text does not describe an AMOC procedure.

10. Cross-check related documents. Use the Honeywell service bulletins cited in the AD and refer to FAA AD 2008-19-12 for additional context and technical references. Ensure any technical work follows the procedures recommended by Honeywell to maintain conformity to the AD’s intent.

Those steps implement the AD’s two mandatory requirements: replacement by the specified trigger and a prohibition on installing listed P/Ns after the effective date. Maintain contemporaneous records of actions taken to demonstrate compliance should the regulator request proof.