AD/CT7/12 Amdt 1 - Stage 2 Turbine Aft Cooling Plate

The AD revolves around a small set of interlocking technical and administrative concepts. The first is the identification of affected hardware by part number and by serial number lists: the parts are stage 2 turbine aft cooling plates with P/N 6064T07P01, 6064T07P02, 6064T07P05 or 6068T36P01, and the specific serial numbers to be inspected are listed in Section 4, Appendix A of the GE ASB Revision 4 (Applicability; Requirement). The AD therefore does not require inspection of every plate of that P/N, only those with the listed serial numbers.

Second, the AD mandates a one‑time non‑destructive test, specifically an eddy current inspection, using the inspection method steps 3.B.(1)-3.B.(3) in the GE ASB Rev 4 or later FAA approved revisions (Requirement 1). The ASB’s procedural steps become normative for compliance; the AD does not set its own inspection method, it adopts the GE ASB’s method and the ASB’s Return to Service Criteria.

Third, the AD sets conditional replacement rules for plates that fail the inspection. The owner/operator has a choice between installing a new plate whose serial number is not on the Appendix A list or installing a plate that, regardless of serial number, meets the ASB acceptance criteria specified in 3.B.(1)-3.B.(3) (Requirement 2). The AD thus links permissible installation to either exclusion from the listed serial numbers or demonstrable acceptance per the ASB.

Fourth, the AD contains a forward‑looking installation prohibition: after the effective date, any listed‑serial-number plate identified in Section 4, Appendix A must not be installed unless it first undergoes inspection as specified (Requirement 3). That prohibition operates at the installation stage as well as for parts in service.

Fifth, the AD includes timing constraints keyed to maintenance events. The inspection action is required at the next engine or hot section module shop visit, or before an additional 6,000 cycles‑in‑service have been accumulated after the effective date, whichever comes first (Compliance 1). The instrument defines what constitutes an "engine or hot section module shop visit" for that timing rule: introduction into a shop that includes separating major case flanges (Definition).

Sixth, the AD recognises earlier compliance work. It grants "previous credit" for ECIs performed before the effective date if those used GE ASB dated 25 February 2003 or Revision 1 (12 March 2003), Revision 2 (9 May 2003) or Revision 3 (23 July 2004) (Previous Credit). Revision 4 of the ASB, dated 12 December 2005, is the reference that identifies affected serial numbers expanded by the manufacturer (Background).

Finally, the AD is an administrative instrument that amends and supersedes prior directives: it supersedes FAA AD 2005‑18‑01 and refers to FAA AD 2007‑08‑01 Amdt 39‑15018 dated 2 April 2007 (Previous Credit/Background). The AD’s stated safety objective is to prevent stage 2 aft cooling plate separation that could cause an uncontained engine failure and aeroplane damage (Background).

The directive affects owners, operators, maintenance organisations, and parts suppliers for aircraft equipped with specific GE CT7 turboprop engine models when those engines have the identified stage 2 turbine aft cooling plates installed. The listed engine models in the Applicability statement are GE CT7‑5A2, CT7‑5A3, CT7‑7A, CT7‑7A1, CT7‑9B, CT7‑9B1, CT7‑9B2, CT7‑9C, CT7‑9C3, CT7‑9D and CT7‑9D2 turboprop engines fitted with stage 2 turbine aft cooling plates of the specified part numbers (Applicability). The Applicability also notes that these engines are installed on, but not limited to, certain CN‑235 and SF340 series aeroplanes; the AD therefore targets engines regardless of airframe, where the specified plates and serial numbers are present.

Maintenance shops and overhaul facilities are specifically implicated because the mandatory inspection timing is tied to an "engine or hot section module shop visit" as defined in the AD: the introduction of the engine or module into a shop that includes separating major case flanges (Definition; Compliance 1). That definition assigns operational significance to the point at which an engine or module undergoes substantial shop intervention.

Parts suppliers and inventory managers are affected by the installation prohibition: from the effective date, any stage 2 turbine aft cooling plates with serial numbers identified in Section 4, Appendix A must not be installed unless inspected per the ASB (Requirement 3). This affects spare parts usage and stock control: parts with listed serial numbers cannot be fitted without prior inspection.

Aircraft operators bear the direct operational cost and scheduling burden of ensuring the ECI is performed at the next applicable shop visit or within 6,000 cycles‑in‑service after the AD’s effective date (Compliance 1). If an inspection fails, operators must source replacement parts that either have unlisted serial numbers or meet the ASB acceptance criteria (Requirement 2). This creates procurement and repair obligations for operators, and workload for maintenance organisations to perform inspections and installations.

Regulators and their delegates are affected in the sense that the AD is an enforceable instrument issued by the Civil Aviation Safety Authority; the amendment is signed by a CASA delegate, which makes the AD binding on Australian aviation participants from its effective date (Signature; Effective date). Finally, because the AD references specific GE ASB revisions and FAA approvals, those responsible for compliance will need access to the cited ASB (Revision 4) and to monitor any FAA‑approved revisions if relying on later methods.

Duties

• Perform a one‑time eddy current inspection (ECI) of stage 2 turbine aft cooling plates with P/N 6064T07P01, 6064T07P02, 6064T07P05 or 6068T36P01 that have serial numbers listed in Section 4, Appendix A of GE ASB No. CT7‑TP S/B 72‑A0464, Revision 4, and that will be returned to service. The inspection must follow 3.B.(1) through 3.B.(3) of GE ASB Rev 4 or later FAA approved revisions (Requirement 1).

• If a plate does not meet the Return to Service Criteria, do one of the two replacement actions specified by the AD: either replace the plate with a new plate whose serial number is not listed in Section 4, Appendix A of the ASB, or replace it with a plate that meets the ASB acceptance criteria in 3.B.(1)-3.B.(3) (Requirement 2).

• From the effective date, do not install any stage 2 turbine aft cooling plates with serial numbers identified in Section 4, Appendix A without inspecting the plate using the ASB procedures (Requirement 3).

• Execute the inspection at the next engine or hot section module shop visit, but before accumulating an additional 6,000 cycles‑in‑service after the effective date, unless the inspection has already been performed (Compliance 1). The AD defines "engine or hot section module shop visit" to clarify this timing (Definition).

Rights and options

• Operators have a prescribed choice if a plate fails inspection: they may either install a new plate with an unlisted serial number or a plate that demonstrably meets the ASB acceptance criteria (Requirement 2). The AD therefore does not mandate use of a particular replacement source or serial number pool beyond excluding listed serial numbers unless inspected.

• Previous compliance credit is expressly provided: eddy current inspections of the stage 2 turbine aft cooling plate boltholes performed before the effective date of the AD using GE ASB dated 25 February 2003, or Revision 1 (12 March 2003), Revision 2 (9 May 2003), or Revision 3 (23 July 2004), satisfy the AD’s requirements (Previous Credit). That confers a retroactive right to count earlier work towards compliance.

• The AD permits use of later FAA approved revisions of GE ASB Rev 4 for performing the inspection (Requirement 1). That means if GE or the FAA publishes an approved revision with updated procedures, operators may use those approved methods.

• The AD limits the requirement to parts with serial numbers listed in the ASB’s Appendix A and to plates that will be returned to service. Thus, parts not listed, or listed parts not being returned to service (for example, those scrapped), fall outside the immediate inspection duty as written.

Operational allocation of duties

• Responsibility to schedule and conduct the specified inspections and replacements rests with operators and maintenance organisations who control engine shop visits and parts installation.

• Parts control and procurement functions must prevent installation of listed serial‑number plates without inspection and must source compliant replacements when required.

• Regulatory oversight is implicit in the AD instrument and effective date; the AD indicates its administrative provenance through the CASA delegate signature and effective date (Signature; Effective date).

The text of the AD provides the directive, the effective date and the supervising authority, but it does not set out a separate schedule of penalties or enforcement procedures within the instrument itself. The document identifies the Civil Aviation Safety Authority as the issuing authority through a delegate signature (David Punshon) and specifies an effective date of 7 June 2007 for the amendment. The AD also states that it supersedes a prior FAA AD and refers to FAA AD 2007‑08‑01 Amdt 39‑15018 dated 2 April 2007 (Previous Credit/Background).

Because the AD is a regulatory amendment issued by the national aviation authority, compliance is mandatory from the effective date as described in the Compliance paragraph. The AD imposes concrete compliance obligations (inspection at the next shop visit or before accruing an additional 6,000 cycles, use of specific ASB procedures, replacement options, and an installation prohibition for listed serial numbers) and thereby creates legally relevant duties for operators and maintenance organisations (Requirement; Compliance). The AD itself does not detail the administrative or civil enforcement mechanisms or penalties that apply for failing to comply. The instrument likewise does not list criminal sanctions, infringement notices, fines, or other enforcement mechanisms within its text.

Practically, the AD’s enforceability is signalled by its formal issuance, the effective date, and its cross‑reference to established maintenance documentation (GE ASB Rev 4 and specified previous ASB revisions). The AD’s background links the directive to a safety hazard , reports of six cracked plates and the stated aim to prevent plate separation and uncontained engine failure , which explains the safety rationale for regulatory enforcement (Background). The AD’s prior‑credit provision and allowance for FAA‑approved ASB revisions establish an administrative path to compliance rather than an open‑ended discretionary exemption (Previous Credit; Requirement 1).

Where enforcement detail is required , for example, whether non‑compliance would be treated as an airworthiness breach under a particular statutory provision, or the sanctions available to CASA , the AD text itself does not provide that material. The AD therefore creates clear operational obligations, sets effective dates, and identifies the regulatory authority, while leaving the specific enforcement mechanisms outside the text of the instrument itself.

The AD expressly interacts with earlier regulatory instruments and with manufacturer service material. It supersedes FAA AD 2005‑18‑01 and refers to FAA AD 2007‑08‑01 Amdt 39‑15018 dated 2 April 2007 (Previous Credit). The AD therefore functions as an amendment in a chain of airworthiness directives addressing the same hardware and hazard, replacing a prior FAA AD in its effect as described.

The AD incorporates external technical guidance by reference. Compliance depends on following 3.B.(1) through 3.B.(3) of GE ASB No. CT7‑TP S/B 72‑A0464, Revision 4, dated 12 December 2005, or later FAA approved revisions of that ASB (Requirement 1). The AD also requires the use of the ASB’s Return to Service Criteria and references the ASB’s Section 4, Appendix A for the serial number list that determines applicability. This means the AD is operationally dependent on the content of the GE ASB and on FAA approvals of subsequent revisions. The AD therefore creates a legal dependency between mandatory regulatory compliance and manufacturer technical material which, in practice, will require operators to obtain and follow that ASB.

The instrument recognises and validates prior maintenance actions performed under earlier ASB revisions. Specifically, it accepts eddy current inspections performed before the effective date using GE ASB dated 25 February 2003 or Revisions 1, 2 or 3 as satisfying the AD’s requirements (Previous Credit). That provision creates a temporal interaction with past practice by excluding certain prior work from the AD’s new inspection burden.

The AD ties its compliance timing to maintenance concepts that have legal and contractual consequences. The "engine or hot section module shop visit" is defined in the AD as the introduction of the engine or module into a shop that includes separating major case flanges (Definition). That definition will interact with operators’ maintenance scheduling, maintenance contracts, and accounting of shop visits for compliance purposes. For example, if another regulatory instrument or operator manual defines shop visit differently, the AD’s definition will be the operative one for this requirement.

The AD does not itself amend other statutes or regulations; it is an administrative amendment that modifies the regulatory duties applicable to specified engines and parts. The AD’s ban on installing listed serial‑number plates without inspection from the effective date interacts with parts installation practices, spare parts inventory controls and procurement decisions. It does not, in its text, provide for exemptions beyond the stated prior‑credit allowance or for alternate methods of compliance other than use of later FAA approved ASB revisions. The AD therefore channels compliance through the GE ASB procedures and through the serial number exclusion mechanism set out in Section 4, Appendix A.

Finally, the AD references both manufacturer documentation and FAA approvals, which indicates cross‑jurisdictional referencing of technical approvals. The AD itself is an Australian amendment; its reference to FAA ADs and FAA‑approved ASB revisions creates a networked regulatory environment in which domestic compliance may depend on foreign technical approvals or earlier foreign directives.

The document on which this deep dive is based is an amendment to an existing airworthiness directive. Key dated milestones and revision interactions stated in the text are:

• GE ASB No. CT7‑TP S/B 72‑A0464, Revision 4, dated 12 December 2005, is the main technical reference used by this AD (Requirement; Applicability).

• The AD refers to earlier GE ASB issuances and provides prior credit for ECI work done using GE ASB dated 25 February 2003, Revision 1 dated 12 March 2003, Revision 2 dated 9 May 2003, and Revision 3 dated 23 July 2004 (Previous Credit).

• The original issue of this AD became effective on 22 December 2005, according to the Background paragraph. The amendment dated 6/2007 becomes effective on 7 June 2007 (Effective date).

• The amendment is described as "AD/CT7/12 Amdt 1", indicating this is Amendment 1 to AD/CT7/12. The header information shows "AD/CT7/12 Amdt 1 | Stage 2 Turbine Aft Cooling Plate | 6/2007", reflecting the amendment notation and month/year.

• The AD supersedes FAA AD 2005‑18‑01, as stated in the Previous Credit paragraph. It also refers to FAA AD 2007‑08‑01 Amdt 39‑15018 dated 2 April 2007.

• The Background paragraph explains the basis for the amendment: the manufacturer expanded the list of affected engine models and identified affected stage 2 turbine aft cooling plates by serial number. This is the proximate reason provided for issuing the amendment.

• The AD bears a delegate signature: "David Punshon, Delegate of the Civil Aviation Safety Authority" with date 24 April 2007, which records the authority authorising the amendment.

Taken together, the AD’s amendment history shows an original AD in late 2005, subsequent GE ASB revisions dating back to 2003 through 2005, and this amendment coming into effect in June 2007 after a delegate signature in April 2007. The AD explicitly notes that some prior inspections conducted under earlier ASB revisions are acceptable for compliance, which indicates an intent to preserve the enforcement value of earlier maintenance actions. The AD’s amendment therefore updates applicability and serial‑number identification while maintaining continuity with prior technical guidance.

The AD text does not provide any court decisions, litigation references, or case names in relation to the directive. The document cites regulatory instruments and manufacturer service bulletins but contains no litigation history or references to judicial review, appeals, or contested enforcement proceedings.

Where the AD does refer to other instruments, those are administrative directives: it supersedes FAA AD 2005‑18‑01 and refers to FAA AD 2007‑08‑01 Amdt 39‑15018 dated 2 April 2007 (Previous Credit/Background). Those cross‑references are to other administrative airworthiness directives rather than to court judgments.

Because the AD defines terms that may be operationally significant , for example, "engine or hot section module shop visit" , and because compliance is tied to serial number lists in an external ASB document (Section 4, Appendix A), factual disputes about whether a particular plate falls within the AD’s scope or whether a particular intervention constituted a shop visit could be the factual bases for compliance disputes. The AD itself, however, contains no description of any prior litigation nor of any judicial interpretations of its provisions.

In short, the source contains no litigation history. Any adjudicative or judicial material related to enforcement, interpretation of the AD’s timing or definitions, or disputes about particular inspections or installations are not contained in the AD text provided.

Several practical traps and operational details in the AD can catch operators and maintenance organisations if not read closely.

• Serial number control is crucial. The AD’s applicability and installation prohibition hinge on serial numbers listed in Section 4, Appendix A of GE ASB Rev 4 (Applicability; Requirement 3). The AD text does not reproduce the serial numbers itself; it requires the operator to consult the GE ASB Revision 4 Appendix A to identify affected parts. Failure to consult the ASB or to correctly identify serial numbers can lead to non‑compliance.

• The inspection requirement is one‑time and conditional on the plate being "returned to service". The AD requires ECI for listed plates "that are listed by serial number in Section 4, Appendix A... and that will be returned to service" (Requirement 1). Parts that are not being returned to service (for instance, those scrapped or permanently removed) are not explicitly required to be inspected under the AD as written, though operational prudence may dictate otherwise.

• Timing is linked to shop visits. The inspection is required at the next engine or hot section module shop visit, or before an additional 6,000 cycles‑in‑service after the effective date, unless already done (Compliance 1). Because the AD defines "engine or hot section module shop visit" specifically as introduction into a shop that includes separating major case flanges (Definition), operators who perform less invasive maintenance that does not meet that definition may not trigger the "next shop visit" clause. However, the 6,000 cycles backstop still applies. Misunderstanding what constitutes a shop visit could lead to missed inspection windows.

• Method of inspection is prescribed. The AD requires use of 3.B.(1) through 3.B.(3) of GE ASB Rev 4 or later FAA approved revisions (Requirement 1). Operators cannot substitute a different ECI protocol unless it is a later FAA approved revision of the ASB. Thinking that any eddy current inspection will do is a potential compliance error.

• Previous credit for older ASB revisions exists but is limited. ECIs performed before the effective date using GE ASB dated 25 February 2003 or Revisions 1-3 are accepted (Previous Credit). However, inspections done under different methods or undocumented older procedures are not covered by this credit clause.

• Replacement options are narrow. If a plate fails the ASB’s Return to Service Criteria, the AD allows replacement only with a new plate whose serial number is not listed in Appendix A or with a plate that meets the ASB acceptance criteria (Requirement 2). Operators cannot rely on ad hoc repairs unless those repairs enable the plate to meet the ASB acceptance criteria.

• Installation prohibition applies from the effective date. From the effective date of the AD, listed serial‑number plates must not be installed without prior inspection per the ASB (Requirement 3). This affects spare inventory practices: a listed plate in stock cannot be fitted without the requisite ECI. The AD does not itself set out transitional inventory allowances.

• Dependence on external document access. Compliance requires access to GE ASB No. CT7‑TP S/B 72‑A0464 Revision 4, and possibly to later FAA approved revisions. Operators who do not obtain or properly apply the ASB content cannot meet the AD’s requirements.

• The AD does not prescribe documentation or record‑keeping requirements in the text. While good practice suggests keeping records of inspections and replacements, the AD does not itself state the records to be kept. This absence can create evidentiary gaps when demonstrating compliance, particularly because the AD accepts prior credit for specific ASB revisions.

• The AD refers to earlier FAA ADs and to FAA approved revisions of the ASB. If an operator relies on a later FAA approved ASB revision to perform the inspection, they must ensure that the revision has FAA approval as required by the AD (Requirement 1). An unapproved or locally modified ASB procedure will not satisfy the AD as written.

Operators and maintenance organisations should ensure they consult the GE ASB Revision 4 Appendix A serial number list, plan shop work consistent with the AD’s shop visit definition and timing, use the specified ASB inspection steps or later FAA approved revisions, and manage spare parts to avoid uninspected installation of listed plates.

Step‑by‑step actions consistent with the AD text:

1. Identify affected engines and parts. Review engine rosters and parts inventories to identify CT7 engine models listed in the Applicability (CT7‑5A2, ‑5A3, ‑7A, ‑7A1, ‑9B, ‑9B1, ‑9B2, ‑9C, ‑9C3, ‑9D, ‑9D2) and find stage 2 turbine aft cooling plates with P/N 6064T07P01, 6064T07P02, 6064T07P05 or 6068T36P01. Cross‑check serial numbers against Section 4, Appendix A of GE ASB No. CT7‑TP S/B 72‑A0464, Revision 4, dated 12 December 2005 (Applicability; Requirement).

2. Obtain the GE ASB Revision 4 and any later FAA approved revisions. The AD makes the ASB the operative inspection procedure. Ensure you have the complete ASB including 3.B.(1)-3.B.(3) (inspection steps), the Return to Service Criteria, and Section 4, Appendix A serial number list (Requirement 1).

3. Schedule inspections at the next applicable shop visit. The ECI must be performed at the next engine or hot section module shop visit defined as the introduction of the engine or module into a shop that includes separating major case flanges, or before accumulating an additional 6,000 cycles‑in‑service after the AD’s effective date, unless already done (Compliance 1; Definition). If a shop visit is imminent, incorporate the ECI into the scope of work. If no such shop visit is planned, ensure the inspection is scheduled before the additional 6,000 cycles expire.

4. Perform the ECI per ASB 3.B.(1)-3.B.(3). Use the prescribed eddy current inspection method and acceptance criteria in the ASB for both detecting and evaluating anomalies (Requirement 1). If using a later FAA approved revision of the ASB, confirm the FAA approval and follow that version.

5. For plates that pass, return to service per the ASB. For plates that fail to meet the Return to Service Criteria, implement one of the two replacement paths in the AD: a) replace with a new cooling plate that has a serial number not listed in Section 4, Appendix A; or b) replace with a cooling plate that meets the acceptance criteria specified in 3.B.(1)-3.B.(3) of the ASB (Requirement 2).

6. Do not install listed plates without inspection. From the effective date, avoid installing any plate with a serial number listed in Appendix A unless it has been inspected in accordance with the ASB (Requirement 3). Apply this rule to spares and to parts returned from overhaul.

7. Apply previous credit where appropriate. If an ECI was performed before the effective date using GE ASB dated 25 February 2003 or Revisions 1-3 (dates specified), that inspection complies with the AD and does not need repeating (Previous Credit). Make sure the prior inspection documentation explicitly references the accepted ASB revision.

8. Record evidence of compliance. Although the AD does not specify record‑keeping requirements, maintain documented evidence of the ASB reference used, serial numbers inspected, dates and locations of shop visit and inspection, and replacement actions taken. Given the AD’s reliance on ASB procedures and prior‑credit rules, contemporaneous records will be the practical means to show compliance with the AD‑specified requirements.

9. Coordinate procurement and inventory controls. Prevent installation of listed serial‑number plates without prior ECI by tagging or segregating affected spares, and source replacement plates with unlisted serial numbers or plates that can be demonstrated to meet the ASB acceptance criteria.

10. Monitor for later FAA approved ASB revisions. The AD allows use of later FAA approved revisions of the GE ASB for inspection procedures. If GE or the FAA issues further approved revisions, confirm their approval status and apply them as appropriate (Requirement 1).

Who decides and who pays

• The operator is responsible for deciding when to schedule the ECI within the AD’s timing constraints and for selecting the replacement option if a plate fails inspection. Maintenance organisations will execute the inspections and perform replacements in accordance with the operator’s maintenance authority.

• The operator (or the entity contracting maintenance) will bear the direct costs of inspections, parts replacements and any associated shop labour. Parts suppliers may be involved in supplying replacement plates but the AD does not allocate cost sharing.

Implementation risks and practical notes

• Ensure the inspection team has the specific ASB 3.B.(1)-3.B.(3) procedures and the proper eddy current equipment calibrated to the ASB’s requirements. Using an incorrect or undocumented method risks non‑compliance.

• Because serial numbers determine applicability, confirm correct plate identity before inspection and before any decision to install or to return a part to service.

• If relying on previous inspections for credit, validate that those inspections were performed under the listed earlier ASB revisions and retain that evidence.

Following these steps will align operational practice with the AD’s explicit requirements: perform the specified ECI, follow the ASB procedures, replace or accept parts per the ASB criteria, and do not install listed serial‑number plates without inspection.