AD/TAY/18 - HP Compressor Stator Vane Tip Clearances

The central concept is HP compressor stator vane tip clearance. This is the gap between the tips of the stationary vanes in the high pressure compressor stages 4 to 9 and the corresponding rotating spacers on the HP compressor rotor. If this clearance is too small, under adverse operating conditions such as manoeuvring, thermal distortion, or vibration, the vane tips may rub against the rotor spacers. The AD characterises such rubs as "heavy" and states they can cause partial loss of rotor spacer material, which may lead to an in-flight shut down.

The AD focuses on a revised vane setting procedure prescribed by a manufacturer's alert service bulletin. This is not a redesign or part replacement; it is a change in how the vanes are positioned during assembly or overhaul. The bulletin presumably provides new tolerances or installation instructions to ensure adequate clearance. Operators must use ASB TAY-72-A1653 Revision 1 or a "later NAA approved revision". The term "NAA approved revision" refers to a revision that has been approved by CASA or another national airworthiness authority that CASA recognises. This means operators cannot simply use any later revision from Rolls-Royce; they must ensure the specific revision has been formally approved by an NAA.

Another key concept is engine shop visit. The AD triggers compliance when the module is disassembled for refurbishment or overhaul. A shop visit is generally when an engine is removed from the aircraft and taken to a maintenance facility for significant work beyond line maintenance. The AD does not define "refurbishment or overhaul" in detail. This leaves room for interpretation: a partial disassembly that does not disturb the HP compressor module might not trigger the requirement, but the AD says "when the module is disassembled". Operators must determine whether a planned shop visit involves disassembly of the HP compressor module to the extent needed to access the stator vanes.

Flight hours are used as an alternative compliance trigger for some models. For Tay 611-8 engines, if both engines on an aircraft are affected, one must comply no later than 5,450 flight hours after the effective date. For 611-8C the limit is 6,800 flight hours since new. Note that "since new" refers to the engine's total flight hours from initial manufacture, not from the effective date. This creates different compliance horizons depending on the engine's age. For older engines with high hours, the deadline may be immediate.

Both engines on an aircraft affected: The AD imposes a special rule for twin-engine aircraft where both engines fall within the applicable engine serial number ranges. In such cases, even if neither engine is due for a shop visit, at least one engine must be brought into compliance by the stated flight hour or calendar deadline. This forces operators to decide which engine to pull early, incurring cost and downtime. The AD does not explain why only one engine needs to be done early while the other can wait until its next shop visit. The rationale may be to reduce the probability of a dual-engine IFSD, but the AD does not quantify the incremental safety benefit.

The AD replaces AD/F100/75, which was narrower in scope. That earlier directive applied only to Tay engines on Fokker F100 aircraft. The new AD removes the aircraft-type limitation, meaning operators of Tay engines on Boeing 727, Gulfstream, or Fokker F28 must now comply even if they were previously exempt. This expansion increases the compliance population without necessarily reflecting new risk data for those other installations. The AD cross-references European Aviation Safety Agency (EASA) AD 2006-0336 dated 13 November 2006, indicating coordination with European regulators.

The AD directly affects any operator or owner of an aircraft powered by Rolls-Royce Tay 611-8, 611-8C, 620-15, 650-15, or 651-54 series engines with specified engine serial numbers. For Tay 611-8 engines, the AD applies to serial numbers prior to 18216. For Tay 611-8C engines, it applies to serial numbers prior to 85055. For Tay 620-15, 650-15, and 651-54 engines, it applies to all engine serial numbers. This means newer engines with serial numbers above those thresholds are exempt for the 611-8 variants, but all 620 and 650 series engines are captured regardless of age.

Aircraft types that commonly use these engines include the Boeing 727 (a three-engine aircraft), Fokker F28 Mark 0070 and Mark 0100 (twin-engine regional jets), and Gulfstream G-IV and GIV-X series (twin-engine business jets). Operators of these aircraft must check each engine's model and serial number. The AD is not limited to those aircraft types; any aircraft with an affected Tay engine is subject to the directive.

The AD imposes duties on maintenance organisations that perform engine shop visits. They must obtain the latest approved version of the alert service bulletin and apply the revised vane setting procedure whenever the HP compressor module is disassembled. This requires training for technicians and updates to maintenance manuals and work cards. For organisations that have their own approved maintenance procedures that differ from the manufacturer's instructions, the AD requires them to follow the ASB procedure unless they have an alternative means of compliance approved by CASA. This reduces flexibility.

Rolls-Royce Deutschland and Rolls-Royce plc are the engine manufacturers and are the source of the alert service bulletin. While the AD does not impose duties on them directly, they are affected in that they must support operators by making the bulletin available and by seeking NAA approval for any later revisions they issue. If a later revision is not approved, operators cannot use it unless they obtain individual approval.

CASA is the regulator issuing the AD. Under the Civil Aviation Act 1988 and Civil Aviation Safety Regulations (CASR) Part 39, CASA has the power to make such directives. The AD also references EASA AD 2006-0336, indicating coordination with European authorities. Operators may also need to comply with the EASA AD separately if their aircraft is registered in Europe.

The expansion of scope from AD/F100/75 means operators of Tay engines on Boeing 727 and Gulfstream aircraft are now affected for the first time. These operators may not have been tracking Fokker-specific ADs, so they may be unaware of the requirement until the new AD is published. This creates a risk of non-compliance due to lack of awareness. Similarly, operators who had already complied under AD/F100/75 on Fokker F100 aircraft may have assumed their obligation was satisfied, but they must confirm that the procedure used meets the new standard. If they used an earlier revision of the service bulletin, they may need to repeat the work.

The AD also affects lessees and financiers: an aircraft with non-compliant engines may lose its airworthiness certificate, affecting asset value and lease terms. Insurance policies may also require compliance with all applicable ADs.

The primary duty is to incorporate the revised HP compressor stator vane setting procedure in accordance with ASB TAY-72-A1653 Revision 1 dated 5 October 2006, or a later NAA approved revision. This duty arises at the specific compliance times set out in the schedule for each engine model.

For Tay 611-8 and 611-8C engines, the duty is triggered at the next engine shop visit after the effective date when the module is disassembled for refurbishment or overhaul. Additionally, if both engines on the aircraft are affected (for 611-8), at least one engine must comply no later than 5,450 flight hours after the effective date. For 611-8C, the limit is 6,800 flight hours since new. This means the operator has a choice: either perform the procedure during a scheduled shop visit that occurs before that flight hour limit, or perform it earlier by bringing an engine to shop. There is no right to defer beyond that limit even if no shop visit is planned.

For Tay 620-15, 650-15, and related variants, the duty is to comply at the next such shop visit, but not later than 1 January 2015. If both engines on the same aircraft are affected, at least one engine must comply before 1 January 2011. This calendar deadline is absolute; it does not depend on flight hours. For an operator with a low-utilisation aircraft, this may force a shop visit many years before the engine would otherwise require overhaul, creating a significant economic burden.

For Tay 651-54 engines, the duty is at the next shop visit but no later than 8,200 flight hours after the effective date.

Operators have the right to use a later NAA approved revision of the service bulletin instead of Revision 1. This allows them to benefit from any improvements or clarifications in later revisions. However, the operator bears the cost of checking whether later revisions have been approved by CASA. The AD does not specify how the operator is to know whether a later revision has been NAA approved. Practically, CASA may issue a new AD or a notice, but there is no guarantee. Operators should monitor the CASA website or contact the manufacturer.

Operators also have the right to apply for an alternative means of compliance under CASR Part 39. For example, if the engine is operated in a way that the vane tip clearance issue does not arise, or if a design change eliminates the risk, the operator could propose a different solution. However, the AD does not mention this explicitly; it is a general right under the regulations. Obtaining such approval may be time-consuming and expensive.

Operators have the duty to maintain records of compliance. While not stated in this AD, CASR Part 39 and airworthiness regulations require operators to document each AD's compliance status, including the date, engine serial number, procedure used, and the person performing the work. These records may be inspected by CASA.

If an operator has already complied under AD/F100/75 at any revision status, the duty is considered accomplished. But this is conditional: the earlier compliance must be in accordance with the same requirement as the new AD. Since AD/F100/75 required a vane setting procedure but of a different scope (only for Fokker F100), operators should verify that the procedure they performed is identical to ASB TAY-72-A1653 Revision 1. If not, they may need to redo the work. The AD does not clarify whether the earlier directive required the same service bulletin.

The AD does not itself state penalties, but it is issued under the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations. Contravening an airworthiness directive is an offence under section 20AB of the Civil Aviation Act. The penalties can be significant. For an individual, the maximum penalty is 50 penalty units (currently AU$11,000) or imprisonment for 2 years, or both. For a body corporate, the penalty is up to 250 penalty units (AU$55,000). These are criminal penalties. Additionally, CASA may issue a civil penalty of up to 1,000 penalty units for a body corporate and 200 for an individual under the Civil Aviation Amendment Act 2020, which introduced a civil penalty regime.

Beyond fines, the most immediate enforcement tool is that CASA may suspend or cancel the aircraft's airworthiness certificate if it is found to be non-compliant. This effectively grounds the aircraft until the AD is complied with. For a commercial operator, the cost of grounding far exceeds the fine. This gives CASA strong de facto enforcement power without needing to go to court.

CASA can also issue infringement notices (on-the-spot fines) for less serious breaches. The AD compliance schedule imposes deadlines; failing to meet them is a breach. Even a timing error (e.g., performing the procedure 100 flight hours late) could result in enforcement action, though in practice CASA may issue a warning for minor delays.

For maintenance organisations, failure to apply the correct procedure when performing a shop visit could lead to revocation or suspension of their maintenance approval under CASR Part 145. This could put the entire business at risk. The AD is mandatory; there is no defence of ignorance. Operators must have systems in place to track AD applicability and compliance status.

The AD cross-references EASA AD 2006-0336. For aircraft registered in Australia but operated overseas, the operator may also have to comply with the European AD. Non-compliance under EASA could result in the aircraft being denied entry into European airspace.

Enforcement is likely to be reactive: CASA may become aware of non-compliance during routine surveillance, incident reports, or if an IFSD occurs that could have been prevented by the AD. If an operator has not complied and an incident occurs, the regulator and possibly the court will view the non-compliance as a serious aggravating factor.

This AD is made under the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations, specifically CASR Part 39, which govern the issuance and compliance with airworthiness directives. Part 39 provides the legal framework for ADs, including requirements for operators to comply and procedures for alternative means of compliance. This AD is a primary instrument under that part.

The AD explicitly interacts with the earlier CASA AD/F100/75 Amendment 1 dated June 2006, which it supersedes and cancels. That AD applied only to Tay engines on Fokker F100 aircraft. The cancellation means that operators who were subject to AD/F100/75 must now comply with AD/TAY/18 instead. However, the new AD allows previous compliance under AD/F100/75 to count, provided it was accomplished at any revision status. There is a potential gap: if AD/F100/75 required a different service bulletin revision or a different procedure, then the prior work may not satisfy the new requirement. The operator must determine whether the earlier procedure matches the revised setting procedure. The AD does not provide a detailed reconciliation.

The AD references EASA Airworthiness Directive 2006-0336 dated 13 November 2006. This is the European equivalent, issued by the European Aviation Safety Agency. For engines installed on aircraft registered in an EASA member state, compliance with that AD is mandatory. For Australian-registered aircraft, this AD is the operative directive, but the EASA AD may be relevant if the aircraft is operated into Europe. Some operators may choose to comply with the EASA AD directly if it is more convenient, but the CASA AD is the binding law in Australia. The note does not make the EASA AD legally binding in Australia, but it indicates that the CASA AD is consistent with it.

The AD also interacts with the manufacturer's service bulletins. Using a later NAA approved revision is permitted, but the operator must ensure that the revision has been approved by CASA or a recognised foreign authority. This creates a dependency on the regulatory process. If Rolls-Royce issues a Revision 2 but CASA has not yet approved it, the operator cannot use it without seeking individual approval. This may delay the adoption of improvements.

For operators who have their own approved maintenance procedures under an Approved Maintenance Program (AMP), the AD overrides any less restrictive procedures. The AMP must be amended to include this AD's requirement at the specified thresholds.

The AD does not interact with other ADs for the same engine; it is standalone. However, there may be other ADs affecting the HP compressor or other modules that require similar or competing modifications. Operators must ensure compliance with all applicable ADs, which may have conflicting deadlines. In such cases, the operator must satisfy both, typically by performing the most restrictive requirement.

This is the original version of AD/TAY/18, bearing the number 1/2007. It was signed on 23 November 2006 by James Coyne, a Delegate of the Civil Aviation Safety Authority. It became effective on 18 January 2007. There are no amendments shown in the source document. The AD supersedes and cancels AD/F100/75 Amendment 1 dated June 2006.

The fact that it supersedes an earlier AD with a different numbering system (F100 series, specific to Fokker F100) indicates that CASA rationalised its AD portfolio for Tay engines. Previously, the AD was targeted at a specific aircraft installation; now it is engine-model specific. This consolidation reduces the number of separate ADs but expands the population.

The AD references an EASA AD (2006-0336 from 13 November 2006) which came before the CASA AD by about two months. This suggests that the issue was first addressed by EASA and then adopted by CASA. The CASA AD is likely substantially similar to the EASA one. The service bulletin cited is Revision 1 dated 5 October 2006. There may have been an earlier revision (original issue) that was not approved in Australia; AD/F100/75 may have referenced that earlier bulletin. The change to Revision 1 may reflect updated clearance data.

No subsequent amendments to this AD are shown. It is possible that later revisions of the service bulletin have been approved by NAA and referenced in later amendments, but the source text does not indicate that. Operators should check the current CASA database to see if AD/TAY/18 has been amended or superseded since 2007. Given the age (2006-2007), it is likely that the compliance deadlines have long passed, but the requirement to use the revised procedure remains in effect for subsequent shop visits. The AD does not have an expiry date; it is in effect until cancelled or superseded.

There is no litigation history mentioned in the source document. Airworthiness directives are rarely litigated in Australia because they are quasi-legislative instruments made under delegated powers. Operators may challenge the factual basis of an AD, but the standard of judicial review is narrow. Under the Administrative Decisions (Judicial Review) Act 1977, a person aggrieved could seek review of the decision to issue the AD on grounds such as lack of evidence or procedural error. However, given the limited scope of safety regulation, courts typically defer to CASA's expertise.

For this specific AD, no reported cases were found. Potential grounds for challenge could have included: (a) that the compliance deadlines were arbitrary or cost disproportionate to risk, (b) that the expansion of scope beyond Fokker F100 was not supported by evidence of similar problems on other aircraft, or (c) that the AD incorporated by reference a service bulletin that was not publicly available. However, the AD appears to have been implemented without litigation.

In a free-market context, the absence of litigation does not imply the AD was well-calibrated. Operators may have chosen to comply rather than incur legal costs, especially given the relatively small engine population. The cost of litigation could exceed the cost of compliance for many operators.

The AD does refer to the earlier AD/F100/75, which itself had an Amendment 1 dated June 2006. That earlier AD may have had its own litigation history, but it is not mentioned. The supersession suggests that CASA recognised the need to broaden the applicability, possibly after discovering the issue on other installations. Whether this was based on new data or a precautionary extension is unclear.

No cases have been found involving this AD or similar ones for Tay engines. In general, Australian aviation safety litigation is rare, and most ADs go unchallenged. Operators who wish to contest an AD must apply to the Administrative Appeals Tribunal for a merits review, but the tribunal generally defers to technical judgments.

1. Expanded applicability from AD/F100/75: Operators who only had Tay engines on Boeing 727 or Gulfstream aircraft may not have been monitoring AD/F100/75 because it was Fokker-specific. They now become subject without prior notice. The AD does not require CASA to individually notify each operator; publication in the legislative instrument is deemed sufficient. Operators must have a system to identify new ADs applicable to their fleet.

2. Both-engine rule: For Tay 611-8, 620-15, 650-15 variants, if both engines on the same aircraft are affected, at least one engine must comply by a deadline that is earlier than the shop visit trigger (e.g., 5,450 FH or 1 Jan 2011). This rule applies even if the aircraft is a three-engine Boeing 727, where "both engines" presumably means any two of the three? The AD says "both engines on an aircraft" - on a three-engine aircraft, if two out of three are affected, does the rule apply? Probably, but the AD is ambiguous. For three-engine aircraft, the rule might be interpreted as "both engines on the same side" or simply "if more than one engine is affected". This is a gotcha for operators of Boeing 727s with multiple affected engines.

3. "Later NAA approved revisions": Operators may assume they can use any later revision of the service bulletin. However, the revision must be approved by a National Airworthiness Authority. If Rolls-Royce issues a Revision 2 that CASA has not yet approved, using it may constitute non-compliance with the AD. The operator must confirm the approval status before using a later revision. There is no central list of approved revisions; the operator may need to contact CASA or check the directive history.

4. Compliance schedule triggers are ambiguous for "engine shop visit": The phrase "when the module is disassembled for refurbishment or overhaul" leaves room for interpretation. If the shop visit involves only partial disassembly that does not access the HP compressor stator vanes, is the AD triggered? Probably not, but the operator must determine whether the work scope includes removal of the rotor spacers. If in doubt, the conservative approach is to perform the procedure anyway, increasing cost.

5. "Engine shop visit" not defined: For Tay 651-54 engines, the requirement is "at the next shop visit after the effective date of this directive when the module is disassembled for refurbishment or overhaul, but no later than 8,200 flight hours after the effective date". If the engine goes to shop but the module is not disassembled, the AD does not trigger. However, if the operator delays disassembly until after 8,200 FH, that would be a breach. So the operator must plan to disassemble the module before that flight hour limit.

6. Prior compliance under AD/F100/75: The AD states "unless accomplished previously in accordance with AD/F100/75 at any revision status". But AD/F100/75 was narrower (Fokker F100 only). If an operator complied on a Tay engine installed on a Boeing 727 using AD/F100/75 (which would have applied only if the engine was on a Fokker F100, so this is unlikely), the prior compliance might count. But if the engine was never on a Fokker F100, the operator could not have complied under that AD. This provision is useless for operators who were not subject to the earlier AD.

7. Calendar deadlines for low-utilisation aircraft: For Tay 620/650 engines, the deadline of 1 January 2011 for at least one engine on dual-engine aircraft is a fixed date, regardless of utilisation. An aircraft that flies only 500 hours per year would have very few flight hours by 2011, yet the operator must still pull an engine for a procedure that may not be needed until a later shop visit. This imposes a disproportionate cost on low-use operators.

8. Multiple engine variants covered in one AD: The AD lumps five engine models together with different compliance schedules. An operator with a mixed fleet must manage separate tracking for each model. The Tay 651-54 has its own schedule; Tay 611-8 and 611-8C have different flight hour limits. Mix-ups could lead to missed deadlines.

Compliance involves four phases: identification, obtaining instructions, scheduling, and execution with record keeping.

Phase 1: Identify affected engines. For each Tay engine in your fleet, determine the exact model designation (e.g., Tay 611-8) and engine serial number. For Tay 611-8, check if ESN is prior to 18216; for Tay 611-8C, prior to 85055; for all other models, all serial numbers are affected. Record each engine's compliance status: whether it has already been modified under AD/F100/75 or under this AD. If already modified under AD/F100/75, confirm that the procedure used was the same as ASB TAY-72-A1653 Revision 1 or later approved revision. If uncertain, treat as non-compliant.

Phase 2: Obtain the approved service bulletin. Obtain a copy of Rolls-Royce Deutschland alert service bulletin TAY-72-A1653 Revision 1 dated 5 October 2006. Also check whether any later revision has been approved by CASA or another NAA. Contact CASA or the manufacturer for the current approved revision status. If using a later revision, keep evidence of NAA approval.

Phase 3: Schedule compliance. Determine the compliance deadline for each engine using the AD schedule.

• For Tay 611-8: Plan to perform the procedure at next shop visit when HP compressor module is disassembled. Additionally, if both engines on the aircraft are affected (i.e., both engines are 611-8 models with ESN <18216), schedule at least one engine to be done no later than 5,450 flight hours from the effective date (18 Jan 2007). For an aircraft with a mix of 611-8 and another model, the rule applies only if both are affected. The 5,450 FH count starts from the effective date, not from the engine's birth.

• For Tay 611-8C: Similar, but the alternative limit is 6,800 flight hours since new. So an engine already with 5,000 hours since new must be done within 1,800 hours regardless of shop visit timing.

• For Tay 620-15, 650-15 variants: Schedule at next shop visit, but not later than 1 Jan 2015. For dual-engine aircraft, at least one engine must be done before 1 Jan 2011.

• For Tay 651-54: Schedule at next shop visit, but no later than 8,200 FH after 18 Jan 2007.

Create a spreadsheet tracking each engine against its deadline. For engines that do not have a scheduled shop visit before the absolute deadline, bring the engine to shop early. This may require removing the engine from the aircraft and transporting it to a suitable maintenance facility. Budget for engine change, transport, and loaner engines if needed.

Phase 4: Execute the procedure. When the HP compressor module is disassembled, ensure the maintenance technician applies the revised vane setting procedure exactly as per the service bulletin. Use only the version that is compliant with this AD (Revision 1 or later NAA approved revision). Document the work in the engine maintenance log, including the bulletin revision used, date, and person who performed the work. Also record that AD/TAY/18 has been complied with.

Phase 5: Maintain records and monitor. Keep records of compliance for each engine for at least the life of the engine. Monitor for any amendments to AD/TAY/18 or later approved revisions to the service bulletin. If a later revision is approved that affects engines that have already been modified, the operator may need to re-do or supplement the work. These records should be available for CASA inspection.

Phase 6: For maintenance organisations. If your organisation performs these shop visits, incorporate the AD requirement into your maintenance procedures manual. Train technicians on the revised setting procedure. Ensure that work orders for affected engines include a step to apply the vane setting procedure per the approved bulletin. Verify engine models and serial numbers before proceeding, as some Tay 611-8 serial numbers above 18216 are exempt.

The primary cost is the shop visit itself, not the parts. However, if the shop visit is forced early, the operator loses the remaining useful life of other components that could have been deferred. This opportunity cost is real but not captured in the AD. For operators with a single aircraft, the interruption to service may be severe. For fleet operators, they may rotate a spare engine. The AD offers no flexibility for operators who can demonstrate equivalent safety through other means; they must apply for an alternative means of compliance, which is a burden in itself.