AD/TFE 731/34 - 1st and 2nd Stage Low Pressure Turbine Rotor Discs

An Airworthiness Directive is a legally enforceable regulation issued by the Civil Aviation Safety Authority (CASA) under the Civil Aviation Act 1988 and the Civil Aviation Regulations 1988. It mandates inspection, modification, or replacement of aircraft components when an unsafe condition exists and is likely to exist or develop in other aircraft of the same type design. This particular AD is designated AD/TFE 731/34 and bears the number 9/2005. It follows a format common to Australian ADs: applicability section defining affected engines and parts, requirement section specifying mandatory actions, compliance section setting deadlines, background explaining the safety rationale, and signature by a delegate of CASA (David Villiers, dated 22 July 2005). The directive relies on the concept of “time in service” (TIS) for compliance deadlines, measured in hours of engine operation. It also uses the concept of “Major Periodic Inspection” (MPI), a scheduled heavy maintenance event typical for turbine engines. The directive introduces a specific definition of “access to the turbine discs” - removal of the tie shaft nut - which is not necessarily the same as merely removing the engine from the aircraft or doing a visual inspection. This definition is crucial because compliance deadline 2 and 3 are triggered by “next access to the turbine discs”, but only when that access reaches the level of tie shaft nut removal. The directive incorporates by reference Honeywell Service Bulletin TFE731 72 3682, which contains the tables listing specific serial numbers of discs that must be replaced. Operators must obtain that service bulletin to identify which individual discs are affected. The directive also notes that the affected engines are installed on, but not limited to, specific aircraft types: Avions Marcel Dassault Mystere Falcon 10 and 50 series, Cessna Model 650 Citation III and Citation VI, Gulfstream Aerospace LP (formerly IAI) 1125 Westwind Astra series, Israel Aircraft Industries 1124 series, Learjet 31, 35, 36 and 55 series, Lockheed Georgia 1329 25 series (731 Jetstar and Jetstar II), Raytheon Corporate Jets (formerly British Aerospace) DH/HS/BH 125 series, and Sabreliner NA 265 65 (Sabreliner 65). This list is illustrative, not exhaustive.

This directive primarily affects owners and operators of aircraft powered by Honeywell TFE731 2 and 3 series turbofan engines that have LP turbine discs produced before April 1991 with serial numbers falling within the three tables of SB No. TFE731 72 3682. Given the aircraft types listed (Falcon 10/50, Citation III/VI, Westwind Astra, IAI 1124, Learjet 31/35/36/55, Jetstar/Jetstar II, BAe 125, Sabreliner 65), the directive impacts corporate flight departments, charter operators, and individuals who own these business jets. It also affects maintenance organisations that perform work on these engines, including approved maintenance organisations (AMOs) holding Part 145 certification under the Civil Aviation Safety Regulations 1998. Engine repair stations authorised to work on TFE731 series engines will need to have access to the Service Bulletin and the ability to perform the disc replacement. Parts distributors and suppliers of turbine discs are also affected because the directive prohibits installation of discs that meet the prohibited criteria after the effective date. The engine manufacturer Honeywell International Inc. is affected to the extent that it issued the Service Bulletin and presumably provides replacement parts; however, the directive imposes no obligations directly on Honeywell (the requirement falls on operators). CASA itself is affected as the issuer and enforcer of the directive. Insurance companies that underwrite hull and liability coverage for the affected aircraft may require proof of compliance as a condition of coverage. Leasing companies that own or finance these aircraft will need to ensure lessees maintain compliance. The directive may also indirectly affect aircraft resale values and marketability, as a non compliant aircraft cannot legally be operated.

The primary duty under this directive is the obligation to replace the affected turbine rotor discs within specified compliance times. For TFE731 2 2J, 2 2N, 2A 2A, and 3 1J engines, replacement must occur within 100 hours TIS after the effective date (1 September 2005). For TFE731 2 series engines (excluding the three named variants), replacement must occur at the next MPI or next access to the turbine discs after the effective date, but within 2,200 hours TIS since the last disc inspection, whichever occurs first. For TFE731 3 series engines (excluding TFE731 3 1J), replacement must occur at the next MPI or next access to the turbine discs after the effective date, but within 1,500 hours TIS since the last disc inspection, whichever occurs first. Additionally, after the effective date, operators must not install any disc that has a serial number in any of the three tables and was manufactured before 1 April 1991. This installation ban applies to any aircraft, even if the engine is not one of the originally affected models. The operator has the right to comply using alternative methods only if CASA grants an alternative means of compliance (AMOC). The source does not mention AMOCs, but under standard CASA practice, operators can apply for one. The directive does not provide a specific right to appeal or seek extension; any relief would need to be sought under general administrative law or through CASA’s exemption powers under the Civil Aviation Act. The duty extends to ensuring that maintenance records are updated to reflect compliance, and that the replacement discs are properly documented. If an operator sells an engine or aircraft, the duty to ensure compliance may transfer, but the directive does not address that. The operator also has a duty to ensure that any maintenance provider it hires is properly authorised and capable of performing the replacement correctly, including torquing the tie shaft nut appropriately and following the Service Bulletin procedures.

The source does not specify the exact penalties for non compliance with this Airworthiness Directive. However, under the Civil Aviation Act 1988 and the Civil Aviation Regulations 1988, contravening an airworthiness directive is a serious offence. Section 20A of the Act makes it an offence to operate an aircraft that does not comply with an applicable airworthiness directive, with maximum penalties including imprisonment for up to two years for individuals and fines for corporations. The Civil Aviation Regulations additionally provide that a person must not operate an aircraft unless it is airworthy, and compliance with ADs is a condition of airworthiness. CASA can issue enforcement actions ranging from administrative sanctions (e.g., suspension of an Air Operator’s Certificate or maintenance approval) to civil penalties and criminal prosecution. In practice, CASA may first issue a corrective action notice or a show cause notice. Failure to comply could result in grounding of the aircraft, revocation of registration, or prohibition on further flights. The directive itself does not create a direct right of action for third parties; however, if an uncontained engine failure occurs due to non compliance, the operator could face civil liability for damages, and insurance policies may be voided. The directive is enforceable at any time, and CASA inspectors may check compliance during routine audits or ramp checks. The burden of proving compliance rests with the operator. Records of compliance must be retained in the aircraft’s technical log or maintenance records. The directive being issued by a delegate of CASA (David Villiers) gives it the same legal force as if issued by CASA itself. The effective date of 1 September 2005 triggers all compliance deadlines.

The directive explicitly references FAA AD 2005 13 07 Amendment 39 14143 in Note 2, indicating that this CASA AD is based on a corresponding US FAA airworthiness directive. This reflects the bilateral aviation safety agreement between Australia and the United States, under which CASA may adopt FAA ADs with or without variation. Compliance with the FAA AD may be required for aircraft operating under US registration, but the CASA AD applies to Australian registered aircraft. If an Australian operator also operates under FAA rules (e.g., on a US registered aircraft), compliance with both directives may be necessary, though they are substantively identical. The directive interacts with the Civil Aviation Safety Regulations 1998 Part 42 (Continuing Airworthiness) and Part 145 (Maintenance Organisations). Part 42 requires the owner or operator to ensure that all applicable ADs are complied with and recorded. Part 145 organisations must have the capability and approval to perform the required work. The directive also interacts with the Civil Aviation Regulations 1988 concerning airworthiness certificates and the requirement to maintain the aircraft in a condition for safe operation. Insurance policies typically require compliance with all applicable ADs as a condition of coverage; failure to comply may void hull and liability insurance. The directive may also interact with bilateral agreements for mutual recognition of maintenance; for example, a maintenance release issued in a foreign country that does not incorporate this disc replacement may not be accepted for return to service in Australia. The directive does not supersede any other AD; it adds to them. Any other ADs applicable to the TFE731 engine (such as those for other components or different serial number ranges) remain in force. The directive also interacts with the manufacturer’s service instructions: while the Service Bulletin is incorporated by reference, compliance with the AD is mandatory whereas the Service Bulletin alone is advisory. The directive does not create any contractual rights between parties; it imposes public law obligations only.

The source presents only a single version of AD/TFE 731/34, identified as Amendment 9/2005, and states it becomes effective on 1 September 2005. There is no indication of any earlier or later amendments to this specific AD within the source document. The document is signed by David Villiers as Delegate of CASA on 22 July 2005, and the effective date is 1 September 2005. No reference to superseded directives or revisions appears. However, it is common for CASA to reissue ADs if errors are found or compliance times are adjusted. For example, an AD may be revised to include additional serial numbers or to extend compliance times if parts are unavailable. Without additional source material, we cannot confirm whether this AD was later amended. The directive notes that it refers to FAA AD 2005 13 07, which may itself have been amended by the FAA. Operators should check the current CASA database for any revisions or replacements of AD/TFE 731/34. The AD number “34” suggests it is the 34th AD issued for the TFE731 engine series, implying a history of prior ADs for the same engine type. The source does not list any of those prior ADs. The directive may have been superseded by a later AD addressing the same or similar unsafe condition. Since the effective date is 2005, it is likely that this AD has been superseded or that the required actions have been accomplished on all affected engines by now. Nonetheless, the source is provided as is, and we must treat it as an enforceable directive that remains in force unless proven otherwise.

The source does not mention any litigation history concerning this specific directive. No court cases are referenced in the text. Airworthiness directives are rarely the subject of direct court challenge; most disputes arise in the context of enforcement actions where an operator contests a penalty. In Australia, there have been challenges to CASA’s power to issue ADs, but generally the courts have upheld the broad discretion of CASA to take action when an unsafe condition is identified. The procedural fairness of AD issuance has been questioned, for example when an AD is issued without prior consultation. However, the urgent nature of safety directives typically justifies immediate effect. The specific AD/TFE 731/34 is based on a report of an uncontained failure, which would provide a strong factual basis for the directive. It is possible that operators affected by this AD sought legal advice about compliance deadlines, particularly the definition of “access to the turbine discs.” Disputes could arise if an operator believed that a different level of disassembly should trigger the compliance time. No reported judgments on this specific AD are known. The FAA counterpart AD (2005 13 07) may have been subject to challenge in US courts, but that is beyond the scope of this source. Without any litigation history provided, the only conclusion is that the source contains no case law. Practitioners should conduct their own searches for any Australian court or tribunal decisions referencing AD/TFE 731/34. Given the age of the directive, it is likely any compliance issues have been resolved, and the directive is now of historical interest except for engines still in service.

Several aspects of this directive trap the unwary. First, the definition of “access to the turbine discs” is highly specific: removal of the tie shaft nut. A maintenance event that opens the engine to inspect the discs but does not remove that nut does not count as “access” for compliance purposes. An operator might assume that any time the turbine module is exposed, the compliance clock restarts. That assumption is wrong. The definition is narrower than common usage. Second, the compliance times are not uniform across all engine variants. There are three different deadlines depending on the exact engine model. Operators must carefully identify the exact model suffix from the engine data plate. Mixing up, for example, TFE731 2 2J with a plain TFE731 2 could mean applying the wrong deadline. Third, the directive applies only to discs initially installed before 1 April 1991. But an operator who buys a used disc without knowing its original installation date may inadvertently install a prohibited disc. The installation ban in paragraph 4 catches anyone who installs a disc with a listed SN that was manufactured before that date, regardless of the engine’s current configuration. Fourth, the directive says “initially installed as new parts before 1 April 1991.” This could be interpreted as meaning the disc’s first installation as a new part occurred before that date. If a disc was manufactured before 1 April 1991 but first installed as a new part after that date, it might not be covered. However, the text of paragraph 4 establishes the manufacturing date criterion for the installation ban. A careful reading suggests two different tests: for replacement requirements, the key is initial installation date; for the installation ban, the key is manufacturing date. An operator could end up with a disc manufactured before 1 April 1991 that was initially installed after that date; that disc would not require replacement under paragraphs 1 3, but it cannot be installed as a replacement part after 1 September 2005. Fifth, the Service Bulletin contains three tables, and the AD cross references them differently for different engine models. Operators must obtain the SB and correlate the serial numbers exactly. Sixth, Note 1 says the engines are installed on “but not limited to” the listed aircraft. So an unusual installation, e.g., on an experimental aircraft, is still covered if the engine model and disc serial number match. Seventh, the directive does not provide an AMOC process; operators must apply to CASA separately if they believe a different inspection method or replacement interval is acceptable.

To comply with AD/TFE 731/34, an operator of an affected aircraft must follow these steps. First, identify all engines in the fleet that are TFE731 2 or 3 series turbofans. For each engine, record the exact model designation (e.g., TFE731 2 2J, TFE731 3 1J) from the engine data plate. Second, obtain a copy of Honeywell International Inc. Service Bulletin No. TFE731 72 3682, dated 26 November 2002. The tables in that SB list specific serial numbers of LP 1st and 2nd stage turbine rotor discs that are suspect. Cross reference each engine’s LP turbine disc part numbers and serial numbers against the tables. Only discs with the specified part numbers (listed in the AD) and serial numbers appearing in the tables are potentially affected. Additionally, determine the initial installation date of each disc. The disc is affected if it was initially installed as a new part before 1 April 1991. Third, for discs that meet the criteria, determine the correct compliance deadline based on the engine model. For TFE731 2 2J, 2 2N, 2A 2A, and 3 1J engines, replacement must occur within 100 hours TIS after 1 September 2005. For other TFE731 2 engines, replacement must occur at the next MPI or next access to turbine discs (tie shaft nut removed) after 1 September 2005, but within 2,200 hours TIS since the last disc inspection, whichever comes first. For other TFE731 3 engines, replacement must occur at the next MPI or next access to turbine discs after 1 September 2005, but within 1,500 hours TIS since the last disc inspection, whichever comes first. If the engine is due for an MPI soon, coordinate the discard replacement with that event. Fourth, schedule the replacement with an approved maintenance organisation (AMO) that holds appropriate rating for Honeywell TFE731 engines. The AMO will need to obtain the replacement discs (new or serviceable used discs that do not meet the prohibited criteria) and perform the work in accordance with the Service Bulletin. Fifth, after replacement, ensure the maintenance records are updated to document the serial numbers of the removed and installed discs, the hours TIS at removal, and the compliance date. Sign off the airworthiness release. Sixth, ensure that no disc with a serial number in any of the three tables and manufactured before 1 April 1991 is ever installed on an engine after 1 September 2005, including as a spare part. Seventh, retain all compliance records for the life of the engine, as CASA may audit them.