AD/TFE731/35 - High Pressure Turbine Rotor Discs Curvic Couplings

The AD is built around four principal operational concepts that determine what operators must do and when.

1. Part identification and serial number lists

• The AD identifies two discrete part numbers: P/N 3075772-1 (for earlier engine subfamilies such as -2C, -3B etc.) and P/N 3060841-1 (for -20R/-40/‑60 families). Compliance is tied not only to part number but to serial numbers listed in Table 1 of the Honeywell service or alert service bulletins (SB No. TFE731-72-3720 and Alert SB TFE731-A72-5185, both dated 5 July 2006). The AD therefore makes the SBs an operational reference: operators must consult the SBs' Table 1 to determine whether an installed disc is within scope.

2. Access definition

• The AD defines "access to the HP turbine rotor discs" specifically as "the removal of the HP turbine rotor assembly from the engine." The compliance trigger of "next access" is therefore defined in narrow mechanical terms: only removal of the rotor assembly counts as access under this AD.

3. CSN drawdown schedule

• The AD establishes two drawdown schedules based on cycles‑since‑new (CSN) at the effective date and a maximum CSN at which removal must occur: for P/N 3075772-1 discs the thresholds are 4,200 CSN (if at or above, remove within 100 cycles-in-service) and a hard stop of 4,300 CSN. For P/N 3060841-1 discs the thresholds are 3,200 CSN (if at or above, remove within 100 CIS) with a hard stop of 3,300 CSN. The AD places an absolute limit on how long an identified disc may remain in service.

4. Inspection and reinstallation control

• The AD requires that any disc removed under the AD must pass a curvic root radius inspection performed by a named Honeywell Certificate Repair Station in Phoenix, Arizona (ZN3R030M) before the disc may be reinstalled. The AD contains no alternative inspection provider or alternative inspection procedure; it conditions reinstallation eligibility on successful inspection by that station.

These concepts create a workflow for affected operators: identify through SB Table 1 whether a fitted disc is affected; check CSN against the drawdown schedule; when the schedule or access requirement is met, remove the HP turbine rotor assembly from the engine; forward discs to the specified Honeywell repair station for curvic root radius inspection; only reinstall discs that pass that inspection.

The AD also cross‑references FAA AD 2008‑02‑19, signalling that the same manufacturing issue has been the subject of corresponding FAA action. The AD's statement of background causation is limited to the manufacturer's report of improperly machined radii in curvic teeth, and the stated consequence the AD aims to prevent is an uncontained HP turbine rotor assembly failure with resulting aeroplane damage.

The AD identifies three overlapping categories of affected parties.

1. Engine operators and aircraft owners

• Operators of aircraft fitted with any of the Honeywell TFE731 variants listed in the "Applicability" section must comply. The applicability explicitly lists a wide range of TFE731 engine variants and provides examples of aircraft installation types: Avions Marcel Dassault Mystere‑Falcon 10 and 50 Series; Cessna Model 650, Citations III, VI, VII; Dassault‑Aviation 20, 50, 50EX, 900, MF900, 900EX (900DX); Gulfstream Aerospace LP (formerly IAI) 1125 Westwind Astra/Astra SPX/Gulfstream 100; IAI 1124 Series Westwind 1124; Learjet 31, 35, 36, 45 (or Learjet 40), and 55 Series; Lockheed‑Georgia 3329‑25 Series (731 Jetstar, Jetstar II); Raytheon Corporate Jets (formerly British Aerospace) Hawker 800/850; Sabreliner NA‑265‑65 (Sabreliner 65). The list is expressly non‑exhaustive by wording “installed on, but not limited to,” so any operator of TFE731 engines of the enumerated series must check applicability.

2. Maintenance organisations and repair stations

• The AD requires removal of HP turbine rotor assemblies and specifies that the curvic root radius inspection must be performed by Honeywell Engines, Systems and Services, Phoenix, Arizona, Certificate Repair Station No. ZN3R030M. That expressly designates a single inspection provider for reinstallation eligibility. Maintenance organisations that perform the removal, transport, and interface with Honeywell's Phoenix facility will therefore be engaged. The AD does not provide alternative repair stations.

3. Honeywell (the manufacturer/service provider)

• Honeywell is both the source of the Service Bulletins containing the list of serial numbers (Table 1) and the provider of the required inspection service. The AD therefore places Honeywell in a central operational role: its SBs identify the affected serial numbers, and its Phoenix repair station performs the mandated inspection that determines reusability of the discs.

Who pays and who decides

• The AD imposes operational requirements upon operators and maintenance providers; the source text does not list funding or indemnity arrangements. By mandating removal, physical inspection, and a named inspection provider, the AD creates direct costs of labour, downtime, transportation, and inspection that will be borne by the operator or the operator's maintenance budget, unless otherwise contractually allocated with Honeywell or insurers. Decisions about compliance timing, logistics for removal, and transport to Honeywell are operational decisions for the operator and the maintenance organisation, constrained by the AD’s removal windows and the requirement that only the specified repair station may perform the qualifying inspection.

Geographic and logistical consequences

• The inspection is required to occur at a named Phoenix, Arizona facility. The AD does not provide domestic Australian inspection alternatives or reciprocal approvals; the source text is silent on local alternatives. For operators outside the USA, this creates an explicit cross‑border logistics requirement embedded in the AD text.

The AD creates specific mandatory duties and defines certain limited rights by implication through its structure. The obligations are prescriptive and tied to parts, serial numbers, cycles‑since‑new, and a specified repair station inspection.

Express duties (from the AD's "Requirement" and "Compliance" text)

• Duty to identify affected discs: Operators must check whether installed HP turbine rotor discs are P/N 3075772-1 or P/N 3060841-1 and whether the disc serial number appears in Table 1 of the respective Honeywell SBs cited (TFE731‑72‑3720 or TFE731‑A72‑5185, both dated 5 July 2006). The AD makes the SB Table 1 the operative list.
• Duty of removal: If an installed disc is within scope, the operator must remove the HP turbine rotor assembly from service according to the CSN‑based drawdown schedule set out in the Compliance section. For discs at or above the higher CSN threshold at the effective date, removal must occur within 100 cycles‑in‑service (CIS) after the effective date. For discs below the threshold at the effective date, removal must occur at the next access to the HP turbine rotor discs, but no later than the hard‑stop CSN specified.
  • For P/N 3075772‑1: remove within 100 CIS if 4,200 CSN or more on effective date; otherwise remove at next access but not to exceed 4,300 CSN.
  • For P/N 3060841‑1: remove within 100 CIS if 3,200 CSN or more on effective date; otherwise remove at next access but not to exceed 3,300 CSN.
• Duty on inspection and reinstallation: Any disc removed under the AD must pass a curvic root radius inspection performed by Honeywell Engines, Systems and Services, Phoenix, Arizona, Certificate Repair Station No. ZN3R030M, before the disc is eligible for reinstallation. This is an absolute precondition to reinstallation in the engine (Requirement 3).

Defined processes and narrow definitions

• "Access" is specifically defined: for the purposes of this AD the removal of the HP turbine rotor assembly from the engine constitutes "access to the HP turbine rotor discs." This narrows the trigger for the "next access" obligation to a mechanically specific act , removal of the HP turbine rotor assembly , and excludes less intrusive maintenance events from counting unless they involve that removal.

Implicit rights and limitations in the AD

• The AD does not specify repair or replacement options beyond the inspection requirement. The AD implicitly permits reinstallation only when the disc passes the specific inspection at the named repair station. The AD does not authorise onsite alternative inspections, third‑party inspection providers, or local certified repair stations unless those are the named Honeywell facility; nor does it provide procedural exceptions within the text. Any operator may choose to remove and scrap an affected disc and replace it with a disc not listed in the SB Table 1, but the AD does not specify replacement pathways, parts availability, or approval processes for alternative parts.

Operational consequence for maintenance scheduling

• The AD compels operators to monitor CSN on the affected discs and to plan removals within the stated windows. That creates scheduling duties for maintenance planners, who must treat the removal deadlines as non‑negotiable constraints on engine utilisation and overhaul planning.

Recordkeeping and evidentiary implication

• While the AD text does not lay out recordkeeping obligations, the compliance schedule is CSN‑based and the AD defines access narrowly. Practically, compliance will require documentary proof of CSN at given dates, of the removal event (the defined "access"), and of the completion of the inspection at the named Honeywell repair station. The AD itself does not specify the form of those records, but the mechanics of compliance create a need for traceable records.

The source text sets out the AD's substantive requirements, effective date and signatory, but it does not set out statutory penalties or civil or criminal sanctions for non‑compliance in the text provided. The instrument is an Airworthiness Directive issued by the Civil Aviation Safety Authority (delegate David Punshon), became effective on 8 May 2008, and references FAA AD 2008‑02‑19, but it contains no express enforcement clause, fine schedule, or remedial enforcement procedure in the copied text.

What the AD does supply relevant to enforcement

• The AD identifies mandatory actions and precise compliance windows and ties reinstallation eligibility to a successful inspection at a specified Honeywell repair station. Those requirements create clear operational checkpoints that regulators, operators, and maintenance organisations can observe or audit: presence of an affected disc, CSN at effective date, date and nature of access events (as defined), removal actions, and inspection results from the named repair station.
• The AD's effective date (8 May 2008) and its compliance timeframes (within 100 CIS for discs above the CSN thresholds or at next access but not beyond the hard‑stop CSNs) define the temporal enforcement window.

What the source does not say

• The AD text as provided does not include an express statement about regulatory enforcement mechanism (for example, mandating grounding or prohibitions on flight with affected discs), civil or criminal penalties, or the administrative process for enforcement actions. It does not quote the Civil Aviation Safety Authority Act or regulations that would articulate penalties for failing to comply. The AD likewise does not include a process for seeking exemptions, alternative methods of compliance (AMOCs), or appeals within the text provided.

Consequences for operators (practical enforcement exposure)

• Because the AD prescribes actions that affect airworthiness‑related components, the practical enforcement exposure for operators will be found in the broader civil aviation regulatory framework that governs maintenance, airworthiness, and operation of aircraft. Although those enforcement mechanisms are not reproduced in the AD text provided, the AD does create tangible compliance markers (removal within stated CSN windows and the requirement for inspection at a named facility) that enforcement authorities can verify against maintenance records, component serial numbers, and inspection certificates.

Administrative follow‑up and cross‑reference

• The AD explicitly references FAA AD 2008‑02‑19 Amdt 15349, dated 16 January 2008. That cross‑reference is informative for inspectors seeking the FAA context or correlated compliance history, but the provided AD text does not import the FAA AD’s enforcement provisions or penalties.

In short, the AD specifies mandatory safety measures and precise compliance timing and inspection providers, but does not itself set out penalties or describe enforcement procedures in the text supplied; enforcement will depend on the regulatory framework to which the AD is attached outside the text reproduced here.

The AD contains a single explicit cross‑reference and otherwise remains self‑contained in the text provided. The following interactions are stated or can be read directly from the AD text.

1. Reference to FAA AD

• The AD explicitly refers to FAA AD 2008‑02‑19 Amdt 15349 dated 16 January 2008. This shows a direct link to a corresponding FAA action on the same manufacturing issue. The AD does not reproduce the FAA AD’s provisions in full within the supplied text, but the cross‑reference indicates that operators and maintainers may need to consult the FAA AD and Honeywell service bulletins together to understand the full operational and historical context. The AD’s reference to the FAA AD is presented as informational in the source text.

2. Reliance on manufacturer service bulletins

• The AD makes the Honeywell Service Bulletin (TFE731‑72‑3720) and Honeywell Alert Service Bulletin (TFE731‑A72‑5185), both dated 5 July 2006, operationally binding for determining which serial numbers are affected (Table 1 in each SB). The AD therefore embeds manufacturer documentation into its compliance regime. Any legal interaction with obligations under maintenance contracts, warranties, or supplier obligations will turn on those SBs as operative lists.

3. Defined inspection provider and cross‑jurisdictional effect

• The AD requires the curvic root radius inspection to be performed at Honeywell Engines, Systems and Services, Phoenix, Arizona, Certificate Repair Station No. ZN3R030M. That embeds a cross‑jurisdictional operational requirement: an Australian AD mandating inspection at a specific U.S. facility. The AD text does not discuss mutual recognition of repair station approvals, import/export of parts, or licensing and approvals for a foreign repair station to perform work on Australian‑registered aircraft. Any regulatory interaction concerning approvals, airworthiness release documentation, or export/import certification will therefore need to be handled under the relevant jurisdictions’ civil aviation regulatory frameworks, but the AD itself does not set those out.

4. Interaction with maintenance scheduling and airworthiness records

• The AD’s CSN‑based drawdown schedule and its definition of "access" create interactions with maintenance planning rules, usage monitoring, and airworthiness record‑keeping. Operators will need to reconcile the AD’s CSN thresholds with their own flight logs, maintenance records, and overhaul schedules. The AD does not specify the form of those records or the evidentiary standard, but the interaction is inherent: proving compliance requires records linking CSN, removal events, and inspection certificates from the named repair station.

5. Absence of alternative methods or exemptions in the text

• The AD does not include in the supplied text any allowance for alternative methods of compliance, equivalence paths, or named exceptions. If an operator wishes to rely on an alternative inspection method or a different repair station, the AD text as provided does not authorise that. Any legal pathway to secure an alternative would therefore have to be sought through the broader regulatory process of the Civil Aviation Safety Authority or other relevant regulatory body; the AD text itself offers no mechanism for that.

6. Practical contractual interactions

• By making Honeywell SB Table 1 the operative list and Honeywell Phoenix the mandated inspector, the AD creates direct contractual and commercial interactions between operators/maintenance organisations and Honeywell. The AD text does not prescribe fee arrangements, timelines for inspection turnaround, or dispute resolution mechanisms; those will be matters of contract negotiation and of the wider regulatory or commercial environment.

In summary, the AD directly interacts with Honeywell service publications and the FAA AD referenced. It mandates inspection at a named US repair station, generating cross‑border operational interactions and creating dependencies that will be resolved through the broader regulatory and commercial frameworks that sit outside the AD text supplied.

The AD text provided contains a limited set of dated references and no multi‑version amendment record within the text supplied. The items in the source that constitute the amendment trail are as follows.

• Honeywell Service Bulletins dated 5 July 2006: The AD relies on two Honeywell documents both dated 5 July 2006 as the source of the Table 1 serial numbers that define affected discs.

  • Honeywell Service Bulletin No. TFE731‑72‑3720 (referenced for P/N 3075772‑1 discs).
  • Honeywell Alert Service Bulletin No. TFE731‑A72‑5185 (referenced for P/N 3060841‑1 discs).

• FAA AD cross‑reference: The AD references FAA AD 2008‑02‑19, Amendment 15349, dated 16 January 2008. That FAA AD appears in the text as a related reference; the Australian AD notes that the FAA AD refers (the AD's Note 2: "FAA AD 2008‑02‑19 Amdt 15349 dated 16 January 2008 refers").

• AD issuance and effective dates in the supplied text:

  • The AD document is headed AD/TFE 731/35 and dated 5/2008 in its table heading.
  • The signatory block reads "David Punshon, Delegate of the Civil Aviation Safety Authority" and is dated 6 March 2008.
  • The AD explicitly states "This Airworthiness Directive becomes effective on 8 May 2008."

What the source does not contain about amendments

• The supplied text does not show any prior versions of this AD, nor does it show later amendments, supersessions, revocations, or revisions. No amendment numbering or subsequent changes are present in the supplied text. There is no version history table or notation of prior AD numbers or later modifications.

Implication for traceability

• The AD’s dependence on Honeywell SB Table 1 and the FAA AD indicates that the practical compliance trail for affected operators will include the 2006 Honeywell SBs and the FAA AD of 16 January 2008. However, the AD text as supplied contains only the dates listed above and does not record any subsequent amendment by CASA. To establish whether the AD has since been amended, superseded or rescinded would require checking the regulatory record beyond the supplied instrument; that information is not contained in the text provided.

The AD text provided does not record or reference any litigation, court decisions, administrative appeals, or judicial review proceedings arising from this AD. The document contains no case names, references to disputes, or indications of legal challenges. The explanatory material supplied is limited to the AD requirements, compliance windows, the Honeywell SB references, and the stated safety background.

What the absence means in practice

• There is no litigation history contained in the text for a reader to analyse. The AD provides operational instructions and a safety rationale; it does not discuss any contentious adjudications, contested enforcement actions, or precedent decisions. Any litigation or dispute record that might exist concerning this AD, the Honeywell parts, or related inspection procedures is outside the scope of the supplied text.

Practical consequence for researchers

• Researchers seeking to know whether this AD has been subject to legal challenge or is the subject of disputes over interpretation, scope, or enforcement will need to consult external regulatory records or court databases. The AD itself provides no such record.

This section flags traps, narrow definitions, dependencies and operational friction that the AD text itself creates or reveals.

1. Inspection is required at a single, named repair station

• The AD requires that "HP turbine rotor discs removed per Requirements 1 or 2 of this AD must pass a curvic root radius inspection performed by Honeywell Engines, Systems and Services, Phoenix, Arizona, Certificate Repair Station No. ZN3R030M before the discs are eligible for reinstallation." The AD provides no alternative inspector, no local equivalent, and no conditional allowance. That single‑provider requirement creates logistics and timing constraints and a dependency on Honeywell’s Phoenix facility. There is no route inside the AD text for a local authorised shop to perform a qualifying inspection.

2. "Access" is narrowly and specifically defined

• The AD defines access to the HP turbine rotor discs as the removal of the HP turbine rotor assembly from the engine. Maintenance actions that do not include removal of the rotor assembly do not count as "access" for triggering the "next access" removal obligation. Operators who commonly perform partial in‑situ inspections or limited accesses may mistakenly assume those count; under the AD they do not.

3. CSN hard stops are tight and model‑specific

• The drawdown thresholds are model/part‑specific: P/N 3075772‑1 discs have a 4,200 CSN trigger and 4,300 CSN hard stop; P/N 3060841‑1 discs have a 3,200 CSN trigger and 3,300 CSN hard stop. Operators must monitor CSN carefully and ensure that maintenance scheduling prevents exceeding the hard stop. If an operator misses the "next access" window and exceeds the maximum CSN, the AD requires removal at that exceeding point; the AD text does not set out transitional relief or extension.

4. Affected serial numbers are in Honeywell SB Table 1 (not printed in the AD)

• The AD depends on Table 1 in the Honeywell SBs to identify affected serial numbers. The AD text does not reproduce Table 1. Operators must obtain and consult the specified Honeywell SBs (both dated 5 July 2006) to determine whether a disc is within scope. Failure to consult the SB Table 1 could lead to misidentifying parts.

5. Potential for scrap or replacement costs not specified

• The AD requires inspection before reinstallation but does not stipulate the outcome if a disc fails the curvic root radius inspection. The AD does not specify whether failed discs may be repaired, must be scrapped, or may be returned to Honeywell for remedial action; that outcome will affect replacement and capital costs. Because the AD does not prescribe an alternative, operators should budget for the possibility that discs may be declared unfit for reinstallation.

6. Cross‑border logistics and regulatory acceptance

• The mandated inspection location is in Phoenix, Arizona. The AD text does not address how an inspection certificate from a U.S. repair station will be accepted for Australian regulatory purposes, or whether import/export documentation will be required for the part. Those procedural steps are left to operators to resolve in the broader regulatory and customs context.

7. Scope phrase "installed on, but not limited to"

• The applicability language includes a long list of aircraft types and then adds "Note 1: These engines are installed on, but not limited to..." That signals that the list is illustrative rather than exhaustive; any aircraft fitted with the listed engine variants is potentially affected. Operators must not rely on the list of aircraft models as exhaustive.

8. AD reference to FAA AD but no integration of FAA compliance options

• The AD notes FAA AD 2008‑02‑19 but does not adopt FAA terms or AMOCs. Operators familiar with FAA processes should not assume that the FAA AD’s procedures or alternative compliance paths are automatically accepted under this AD.

9. No explicit remediation or alternative method in the AD text

• The AD does not specify an alternative method of compliance, temporary relief, or route for obtaining approval for an alternate inspector. If operators require relief, they will need to engage with the relevant authority or Honeywell; the AD text itself contains no mechanism.

10. Timing discrepancy between signatory date and effective date

• The AD is signed 6 March 2008 but has an effective date of 8 May 2008. Operators should use the effective date for compliance counting, not the signatory date. The compliance windows count from the effective date as stated.

Each of these "gotchas" is present in the AD text provided and creates specific operational or compliance risk for operators and maintenance providers.

This section sets out an operational checklist of actions that flow directly from the AD text and that operators or maintenance planners must perform to meet the AD’s requirements.

1. Obtain the referenced Honeywell Service Bulletins

• Secure copies of:
  • Honeywell Service Bulletin No. TFE731‑72‑3720, dated 5 July 2006 (for P/N 3075772‑1 discs).
  • Honeywell Alert Service Bulletin No. TFE731‑A72‑5185, dated 5 July 2006 (for P/N 3060841‑1 discs).
• Consult Table 1 in each SB to confirm whether the serial number of any installed HP turbine rotor disc appears in the list. The AD ties applicability to those serial numbers.

2. Identify installed HP turbine rotor discs and record CSN

• For each engine of the applicable TFE731 variants, confirm if the installed HP turbine rotor disc is P/N 3075772‑1 or P/N 3060841‑1. If so, check the disc serial number against Table 1 of the relevant Honeywell SB.
• Record cycles‑since‑new (CSN) for each identified disc as of the AD’s effective date (8 May 2008). The compliance schedule uses CSN at the effective date as the trigger for the removal windows.

3. Apply the drawdown schedule

• If the disc is P/N 3075772‑1 and its CSN on the effective date is 4,200 or more, plan removal of the HP turbine rotor assembly within 100 cycles‑in‑service (CIS) from the effective date. If the disc’s CSN is less than 4,200, remove the HP turbine rotor assembly at the next access (as defined), but no later than 4,300 CSN.
• If the disc is P/N 3060841‑1 and its CSN on the effective date is 3,200 or more, plan removal of the HP turbine rotor assembly within 100 CIS from the effective date. If the disc’s CSN is less than 3,200, remove the assembly at the next access (as defined), but no later than 3,300 CSN.
• Note: The AD defines access to the HP turbine rotor discs as the removal of the HP turbine rotor assembly from the engine. Only that removal satisfies the "next access" trigger in the AD.

4. Plan maintenance scheduling and logistics

• Schedule the removal of the HP turbine rotor assembly to meet the CSN windows. Coordinate maintenance slots so that the removal occurs within the 100 CIS window if applicable, or at the next defined access before the hard‑stop CSN.
• Anticipate engine downtime associated with removal and account for ferry flights, substitution engines, or scheduled maintenance to avoid exceeding CSN limits.

5. Arrange inspection with Honeywell Phoenix repair station

• After removal, arrange for the curvic root radius inspection to be performed by Honeywell Engines, Systems and Services, Phoenix, Arizona, Certificate Repair Station No. ZN3R030M. The AD mandates this specific station for the inspection that governs eligibility for reinstallation.
• Confirm Honeywell’s procedures for shipping, turnaround times, inspection certificates, and disposition options in case of a failed inspection.

6. Maintain documentary evidence

• Keep records showing:
  • The serial number of the HP turbine rotor disc and evidence that it appears (or does not appear) in Table 1 of the Honeywell SB.
  • The CSN at the AD effective date and the CSN at removal, to show compliance with the drawdown schedule.
  • Evidence of the removal event (work order, maintenance log) demonstrating that "access" as defined was performed.
  • Honeywell Phoenix inspection report and any certification or acceptance documentation proving the disc passed the curvic root radius inspection before reinstallation (or the disposition if it failed).

7. Reinstallation only after successful inspection

• Do not reinstall any disc removed under the AD until it has passed the curvic root radius inspection performed by Certificate Repair Station No. ZN3R030M. The AD makes the inspection result a precondition to reinstallation.

8. Contingency planning for failed inspections

• Establish plans and budgets for replacement parts or repaired discs if a disc fails the Honeywell inspection. The AD does not specify repair options; operators will need to negotiate options with Honeywell or locate approved replacement parts.

9. Communicate with regulators as required

• While this AD text does not include explicit administrative procedures, operators should ensure their airworthiness records reflect compliance and be prepared to provide documentation to the Civil Aviation Safety Authority or equivalent oversight body upon request.

10. Monitor for related advisory material

• The AD references FAA AD 2008‑02‑19 and Honeywell SBs. Operators should monitor Honeywell communications and regulator notices for any further guidance, alternative methods of compliance, or updates that affect the AD’s requirements or approved inspection pathways.

This checklist follows directly from the AD’s requirements and compliance sections as presented in the text: identification via SB Table 1, CSN‑based removal windows, the definition of access as removal of the rotor assembly, and the mandatory inspection at Honeywell Phoenix prior to reinstallation.