AD/AL 250/86 Amdt 3 - Compressor Adaptor Coupling

The Directive operates by two parallel mechanisms: mandatory retirement of specified part numbers, and mandated installation/fitment procedures for approved replacement parts. The main concepts are:

• Applicability by engine model and coupling part number: The AD applies to Rolls‑Royce 250‑B17 and selected 250‑C20 series engines with compressor adaptor couplings listed in Table 1. Table 1 lists affected part numbers by manufacturer: Alcor (P/Ns 23039791AL, 23039791AL‑1/‑2/‑3), EXTEX (A23039791, E23039791, E23039791‑1/‑2/‑3, EH23039791, EH23039791‑1/‑2/‑3), RRC (23039791‑1/‑2/‑3), and SAP (A23039791). The Directive also lists representative aircraft models in Table 2 (various helicopter types and the BN‑2T aeroplane) to orient operators.

• Risk trigger and policy purpose: CASA records nine reports of engine shutdowns caused by compressor adaptor coupling failure. The Directive explicitly states that background as the basis for removal and remedial measures. The measure is framed as safety‑protective: remove suspect parts and replace them with parts and fits specified to avoid fretting and coupling failure.

• Differentiated compliance windows: The Directive assigns different removal deadlines depending on manufacturer and hours‑since‑new. For Alcor couplings the deadlines are shortest (remove within 50 additional operating hours if the coupling has 600+ operating hours or hours unknown; otherwise remove before reaching 650 hours‑since‑new). For EXTEX and SAP the deadlines are longer (100 hours if 600+ or unknown; otherwise within 150 additional hours if under 600). For RRC couplings the Directive permits deferral to the next disassembly for any reason, but not later than 1 March 2017, subject to multiple safety and maintenance record conditions; additionally, if RRC couplings are not Rolls‑Royce manufactured, replacement is required by the compliance date of revision 2 (1 March 2012).

• Technical installation requirements and tolerances: When fitting a replacement coupling, the Directive requires selecting a larger dash size and machining the impeller ID to a fit of 0.0000 to ‑0.0013 inch interference; heating the impeller per overhaul manual during installation; and a ban on plating the impeller ID. It forbids installing a -1 coupling into a used impeller and requires a new impeller if a -3 coupling is to be fitted when a -3 was removed. Fluorescent penetrant inspection of the impeller is mandated and mating surfaces must be free of fretting. Table 3 lists adaptor ODs for replacement adaptors P/Ns 23076559‑1, ‑2, ‑3 and the target fits.

• Cross‑reference to other technical materials: The Directive refers to FAA AD 2004‑26‑09 Amdt 39‑13921 and to Rolls‑Royce Commercial Engine Bulletin CEB‑A‑1392, plus RRC mandatory bulletins and the engine Operations and Maintenance Manual. Those references function as technical and procedural inputs into determining eligibility for deferred compliance and for proper repair/overhaul procedures.

• Definition of "next access": The Directive defines next access as when the compressor module is separated from the engine and disassembled for any reason. That definition anchors the timing of work and creates a de facto trigger for replacement when routine maintenance leads to module separation.

These concepts set the operational mechanics: owners/operators must identify affected couplings, decide which compliance pathway applies (immediate removal vs deferred to next access), and implement the prescribed machining and inspection regime when fitting approved replacement adaptors. The Directive couples date‑based deadlines with part‑status rules and technical fit specifications to mitigate the failure mode CASA observed.

The Directive affects multiple, concrete cohorts; the source lists the affected equipment and prescriptive actions, from which affected persons and organisations follow directly.

• Aircraft owners and operators: Operators of aircraft that use the listed Rolls‑Royce/Allison 250‑B17 and 250‑C20 series engines are primary duty‑holders. Table 2 lists helicopter types (Agusta A109 variants; Bell 206A/B/L; Enstrom TH‑28, 480 variants; Eurocopter AS355 variants; Eurocopter Deutschland BO‑105C/S; MDHI 369 variants; Schweizer 269D) and aeroplanes (BN‑2T) on which those engines are installed; operators of other types may also be affected if they have the covered engines. Owners and operators must determine whether their engines have the listed coupling P/Ns, compute hours‑since‑new, and comply with removal and replacement windows.

• Maintenance organisations and overhaul facilities (AMOs/repair stations): The Directive mandates precise machining tolerances (impeller ID to achieve a fit of 0.0000 to ‑0.0013 inch), fluorescent penetrant inspection, heating per overhaul manual for installation, prohibitions on plating, and prohibitions on certain installations (for example, do not install a -1 coupling into a used impeller). These are actions performed by maintenance organisations or certified overhaul facilities, who therefore bear the technical compliance burden and the risk of rework if procedures are not followed.

• Parts manufacturers, distributors and shippers: Manufacturers and parts suppliers of couplings and impellers (Alcor, EXTEX, RRC, SAP and makers of replacement P/Ns 23076559‑1/‑2/‑3) are affected because their specific P/Ns are either removed from service or prescribed as replacements. The AD explicitly treats non‑RRC manufactured parts as disqualifying for RRC deferred compliance, creating a supply‑control effect: only Rolls‑Royce‑manufactured parts satisfy the conditions for deferral.

• Aircraft engineers, inspectors and record‑keepers: The RRC deferral pathway is conditional on maintenance records demonstrating proper maintenance and on accomplishment of all mandatory RRC bulletins and Commercial Engine Bulletin CEB‑A‑1392. Engineers and inspectors therefore must assess historical maintenance records, resolve unknown hours histories, and document compliance steps. They must also apply the AD's definition of "next access" to flag upcoming disassemblies.

• Operators of non‑listed aircraft types where the engines are installed: The Directive states engines are installed on, but not limited to, the aircraft in Table 2. That wording signals that any operator with the affected engine and listed coupling P/Ns is in scope even if their airframe model is not in Table 2.

Who pays: The source imposes the working, parts, machining, inspection and downtime costs on operators/owners and their maintenance providers. Replacement couplings (specified P/Ns 23076559‑1/‑2/‑3), new impellers when required, machining labour, fluorescent penetrant inspection, and possible extended maintenance windows are direct commercial costs. Indirect costs include aircraft out‑of‑service time and logistical costs to obtain approved parts; these costs are not quantified in the Directive.

Who decides: CASA, via its delegate Mike Higgins, issued the AD. The AD sets rules that owners, operators and maintenance organisations must follow; the AD also delegates technical reference decisions to RRC materials (mandatory bulletins, CEB‑A‑1392) and the engine overhaul manual for heating instructions. Maintenance organisations and engineering authorities must interpret and apply those technical references to meet the AD conditions.

Behavioural changes: Operators must prioritise inspection of parts lists and maintenance records, adjust maintenance planning to satisfy the AD deadlines (including potential unscheduled removals), procure specified replacement adaptors and possibly new impellers, and ensure that repair/overhaul work meets the specified machining tolerances and inspection requirements. Parts distributors and manufacturers must reconcile inventories against the banned P/Ns and may need to manage returns or scrap of affected couplings.

The Directive creates explicit duties, procedural conditions, and technical rights (permitted actions) for affected parties. All duties described below are rooted in the text of the AD.

Duties

• Identify affected parts and engines: Owners/operators must determine whether their Rolls‑Royce 250‑B17 or C20 series engines have the compressor adaptor couplings listed in Table 1 (Alcor, EXTEX, RRC, SAP part numbers). The Directive applies to engines with those P/Ns installed.

• Remove specified couplings from service within the prescribed windows: The AD specifies manufacturer‑specific compliance windows tied to operating hours‑since‑new and calendar deadlines:

  • Alcor (Requirement 1): For couplings with 600 or more operating hours‑since‑new as of the AD's effective date, or where hours are unknown and cannot be determined, remove the coupling within 50 additional operating hours after the effective date or by 15 June 2005, whichever occurs later. For couplings with fewer than 600 operating hours‑since‑new on the effective date, remove before exceeding 650 hours‑since‑new or by 15 June 2005, whichever occurs later.

  • EXTEX and SAP (Requirement 2): For couplings with 600 or more operating hours‑since‑new as of the effective date, or where hours are unknown and cannot be determined, remove within 100 additional operating hours after the effective date or by 15 June 2005, whichever occurs later. For couplings with fewer than 600 operating hours‑since‑new, remove within 150 additional operating hours after the effective date or by 15 June 2005, whichever occurs later.

  • RRC (Requirement 3): Compliances deferred to the next time the compressor rotor is disassembled for any reason, but not later than 1 March 2017, subject to the conditions in (a)-(f) (power assurance history, absence of recent chip lights or metal in oil, mandatory RRC bulletins complied with, proper maintenance records per OMM, compliance with CEB‑A‑1392 when next due, and parts related to the CEB/AD manufactured by Rolls‑Royce). If the parts are not Rolls‑Royce manufactured, RRC couplings must be replaced by the compliance date of revision 2 of the AD (1 March 2012).

• Follow installation and machining procedure for replacement couplings (Requirement 4): When installing a replacement coupling, operators and maintenance organisations must machine the compressor impeller as set out: select a larger dash size coupling and measure the pilot OD; example: if a -1 coupling removed, a -2 must be installed; if a -3 is removed, a new impeller is required; machine impeller ID to achieve fit 0.0000 to ‑0.0013 inch; no fretting allowed on the impeller after machining; plating of impeller ID is not allowed; perform fluorescent penetrant inspection; install new adaptor P/N 23076559‑2 or -3, or if a new impeller is installed, P/N 23076559‑1; heat the impeller per the overhaul manual to achieve the target fits shown in Table 3; mating surfaces must not have fretting; do not install a -1 coupling into a used impeller.

• Observe the AD definition of "next access": The AD defines "next access" as separation and disassembly of the compressor module for any reason. This anchors deferred compliance for RRC couplings to physical maintenance events.

• Ensure compliance with RRC bulletins and CEB‑A‑1392: For RRC deferred compliance to apply, the engine must have had all mandatory RRC bulletins accomplished within their designated compliance requirements, and compliance with CEB‑A‑1392 remains applicable at the next time the compressor is due for repair or overhaul.

Rights and permitted actions

• Use of specified replacement parts: The AD grants permission to install specified new compressor adaptor couplings P/Ns 23076559‑1, -2 or -3, subject to the machining and installation conditions set out. It specifies which adaptor OD ranges and the target interference fit (Table 3).

• Deferred compliance for RRC parts under conditions: The AD permits, as an alternative to immediate removal, deferred removal of RRC couplings to next compressor disassembly (but no later than 1 March 2017) if the engine satisfies the enumerated safety and maintenance conditions. This is a conditional right to defer immediate removal.

• Continued operation until next access for eligible RRC couplings: Where the RRC conditions are met, operators may continue using the affected coupling until the compressor is next disassembled, provided the other conditions in the AD are satisfied.

Prescriptive limitations and prohibitions

• No impeller ID plating: The AD explicitly prohibits plating of the impeller ID.

• No installation of -1 coupling in used impeller: The AD states "Do not install a -1 coupling into a used impeller."

• Fretting prohibition: Mating surfaces of impeller and coupling must not have any fretting; after machining, no fretting is allowed on the impeller.

• Replacement of non‑RRC parts if relying on the RRC deferral exception: If parts related to CEB/AD are not Rolls‑Royce manufactured, RRC couplings must be replaced by the stated compliance date (revision 2 compliance date 1 March 2012). The AD thereby limits the availability of the deferral option to engines with original RRC parts.

Record‑keeping consequences: The AD’s conditions for RRC deferral hinge on maintenance records showing adherence to OMM and mandatory bulletins. That places a record‑keeping duty on operators and maintenance organisations to establish entitlement to any deferral pathway.

The Directive does not set out in text any further rights such as compensation, cost recovery, or appeals procedure; it sets operational duties, technical installation permissions, and conditional deferral rights rooted in maintenance history and parts provenance.

The AD text does not include an express penalties schedule or a separate enforcement section that specifies fines or statutory sanctions within its own wording. What the Directive does provide is a set of mandatory requirements and compliance timeframes issued by the Civil Aviation Safety Authority, signed by the CASA delegate. From the instrument itself one can extract the following enforcement‑relevant features and the limits of what the source records:

• Source of authority and formal effect: The Directive is issued by CASA, signed by the Delegate of the Civil Aviation Safety Authority (Mike Higgins) with an effective date of 8 March 2012. As an AD issued by CASA, the document functions as a mandatory airworthiness requirement: it prescribes removals, inspections, machining and installation practices and compliance dates.

• Compliance code referencing: The AD includes the notation "Compliance Code 4" associated with the compliance requirements. The AD text does not define the meaning of "Compliance Code 4" within the document. The presence of such a code indicates an internal classification of compliance urgency or process, but no definition, penalty, or enforcement mechanism for that code is included in the Directive text.

• Conditional deferral linked to maintenance records and bulletins: The RRC deferral depends on documented maintenance history, absence of recent chip lights or metal in oil events, and compliance with mandatory RRC bulletins and CEB‑A‑1392. From an enforcement perspective, that creates an evidentiary standard: an operator seeking to continue using an RRC coupling past the initial effective dates must be able to show records and evidence that the conditions are met. The AD itself establishes these as necessary conditions; it does not specify the checking, audit or penalty regime for failing to show those records.

• No express statement of penalties within the text: The AD does not state specific legal sanctions (monetary fines, grounding orders, licence suspensions) within its own text. It also does not set out an administrative process for enforcement or appeal. The document therefore leaves unspecified in its text what enforcement actions CASA may take for non‑compliance, relying on the general regulatory framework the issuing authority operates under. The AD does reference FAA AD 2004‑26‑09 Amdt 39‑13921 as a related rule, but does not import any enforcement language from it.

Practical enforcement implications that follow from the Directive (but are not explicitly defined in the AD text):

• Compliance documentation and audits: Because the AD ties deferred compliance to maintenance records and completion of mandatory bulletins, operators will need to produce records on demand to demonstrate compliance. The AD therefore increases the evidentiary burden on operators when inspected.

• Airworthiness and operational legality: Operating an aircraft with an affected coupling beyond the AD’s mandated removal window, without meeting the RRC deferral conditions, would place the aircraft in a condition not conforming to the AD’s requirements. While the Directive itself does not list sanctions, failure to comply with a CASA AD typically has consequences under the broader aviation regulatory framework; those consequences are however not delineated in the AD text and are outside the document’s content.

In summary, the Directive sets mandatory actions, timeframes and documentary conditions but does not within its text specify particular penalties or the enforcement process. The AD creates enforceable duties by being an instrument of CASA; the precise sanctions and enforcement mechanisms are not detailed in the provided source.

The Directive expressly cross‑references external technical and regulatory instruments and conditions that create interaction points with other sources of authority and practice. The AD itself does not purport to amend other legislation; rather it requires compliance actions that depend on or reference other technical documents and regulatory materials:

• Reference to FAA AD: The AD includes a Note that refers to FAA AD 2004‑26‑09 Amdt 39‑13921. That cross‑reference signals technical alignment or commonality of purpose with an FAA airworthiness directive dealing with the same failure mode. It creates an interaction in practice: operators who already complied with the FAA AD might use the FAA AD and its documentation as part of their records when demonstrating compliance to CASA. The AD, however, does not transmute FAA regulatory language into CASA enforcement language; it simply references the FAA AD as related material.

• Dependence on Rolls‑Royce documentation: The RRC deferral conditions require that "All mandatory bulletins issued by RRC have been accomplished within the designated compliance requirements," and that "Compliance with Commercial Engine Bulletin (CEB)‑A‑1392 latest revision is still applicable next time the compressor is due for repair or overhaul." These references make compliance with manufacturer bulletins and CEBs an interacting obligation. The AD effectively makes compliance with certain manufacturer technical directives a gating condition for the CASA deferral. That links CASA’s AD to manufacturer technical compliance regimes and potentially to contractual or warranty relations between operators and RRC.

• Interaction with Operations and Maintenance Manual (OMM): The AD requires that maintenance records indicate proper engine maintenance performed per the applicable OMM. This gives the OMM evidentiary weight under the AD: OMM compliance both shapes the substantive maintenance standard and supplies the documentary basis for deferral eligibility.

• Parts provenance and supply chain: The AD conditions relief for RRC couplings on the parts being Rolls‑Royce manufactured. If parts are not Rolls‑Royce made, they "must be replaced by the compliance date of revision 2 of this AD (1 March 2012)." That condition touches on supply chain and parts‑re‑manufacture status, and therefore intersects with commercial contracts and parts traceability obligations under aviation commerce and maintenance rules.

• No express mention of civil penalty statutes or administrative enforcement processes: The AD does not cite particular enforcement statutes or administrative penalty provisions. The mechanism for enforcement would be supplied by the broader CASA regulatory framework and aviation safety legislation, but the Directive text itself provides no cross‑reference to those statutory enforcement provisions.

• Temporal interaction with amendment history: The AD is an amendment (Amendment 3) to an earlier Directive originally effective in 2005. It modifies compliance windows and extends some dates. That amendment process demonstrates how CASA’s ADs function over time, interacting with prior instruments (Amendments 1 and 2) and with revision dates that become compliance milestones.

In practical terms, the AD creates an operational intersection between CASA regulatory authority, FAA ADs, Rolls‑Royce mandatory bulletins and commercial engine bulletins, and the engine OMM. Operators will need to coordinate compliance across these documents to both satisfy CASA’s immediate requirements and to substantiate eligibility for deferred compliance where allowed in the AD. The AD does not explicitly integrate with statutes setting out penalties, but its status as a CASA AD places it within the regulatory regime that can be enforced under aviation safety law.

The Directive contains its own amendment history and dates in the text. The source provides the following chronological sequence and changes:

• Original issue effective 17 March 2005: The first issuance of this Directive began on that date. The source states "The original issue of this Directive became effective on 17 March 2005."

• Amendment 1 effective 22 March 2005: Amendment 1 "amended the compliance period." The Directive records that Amendment 1 became effective on 22 March 2005. That amendment adjusted the time windows for compliance, although the AD text does not provide Amendment 1’s exact edits beyond the statement that the compliance period was changed.

• Amendment 2: The source records that Amendment 2 "corrected a typographical error in Table 2 of the Applicability and removes the discrepancy in the compliance times for EXTEX and SAP couplings." The AD text indicates Amendment 2 addressed typographical and compliance-time consistency issues between EXTEX and SAP coupling deadlines. No effective date is explicitly stated for Amendment 2 in the fragmentary history text, but its content is recorded.

• Amendment 3 (this document) becomes effective 8 March 2012: Amendment 3 extends the compliance date for RRC compressor adaptor couplings, subject to the stated conditions. The Directive explicitly states: "This Amendment becomes effective on 8 March 2012." The top of the document shows "AD/AL 250/86 Amdt 3" and the date 5/2012, and it is signed by Mike Higgins as Delegate of CASA on 8 March 2012.

• Specific compliance‑date adjustments within Amendment 3: Amendment 3 sets the RRC couplings deferral to "At the next time the compressor rotor is disassembled for any reason, but not later than 1 March 2017, subject to the following conditions..." It also states that if parts related to the CEB or AD are not Rolls‑Royce manufactured, "RRC Compressor Adaptor Couplings must be replaced by the compliance date of revision 2 of this AD (1 March 2012)." That creates a distinctive compliance deadline that precedes the Amendment 3 effective date, which is recorded as a matter of the AD text.

• Rationale for amendments: The background paragraph states: "This AD results from nine reports of engine shutdown caused by compressor adaptor coupling failure. Amendment 3 compliance date extended for RRC compressor adapter couplings, subject to the stated conditions. Amendment 2 corrected a typographical error in Table 2 of the Applicability and removes the discrepancy in the compliance times for EXTEX and SAP couplings. Amendment 1 amended the compliance period." That statement assigns the driver for the original AD (reports of engine shutdowns), and explains the content of the subsequent amendments: Amendment 1 shortened/changed compliance timing, Amendment 2 corrected accuracy and harmonised compliance times, and Amendment 3 extended the RRC compliance date under conditions.

• Compliance Code 4: The text includes "Compliance Code 4" connected to the compliance schedule. The AD does not define what "Compliance Code 4" means in the document itself, but it is part of the recorded amendment.

• Practical effect of the amendment sequence: Over time CASA adjusted the directive to reconcile typographical errors, harmonise deadlines for different manufacturers, and to provide a conditional extension specifically for RRC couplings,linking the extension to maintenance history, mandatory bulletins, and parts provenance.

This is the full amendment history recorded in the AD text. No further legislative or revision history is recorded in the source beyond the original issue and the three amendments described.

The Directive text contains no litigation history. It records the safety basis (nine reports of engine shutdown caused by compressor adaptor coupling failure) and documents successive amendments, but it does not report any judicial or administrative challenges, appeals, or court decisions related to the AD.

Because the source is the AD itself, it does not include information about enforcement actions, disputes, or litigation outcomes. The document therefore provides no material to indicate that the AD has been the subject of judicial review, injunction proceedings, contractual claims, or litigation between operators, manufacturers and regulatory authorities.

Practitioners wanting litigation or case history will need to consult administrative records, CASA enforcement logs, court databases or industry publications outside the text of this AD. The AD does not assert any such outcomes nor does it report controversies in its own continuation or amendment.

Given the absence of litigation data in the source, users should not infer from the AD text alone that there has been no litigation; the AD contains simply no record of any legal proceedings. Any claim about litigation or legal challenges must be sourced independently from materials other than this Directive.

The AD contains several precise technical, timing, and evidentiary conditions that can create pitfalls for operators and maintenance organisations if not read and applied carefully. The following are concrete "gotchas" drawn from the text,the specific mechanics that commonly cause compliance or interpretation errors.

• Different manufacturers have different compliance windows, and "unknown" hours are treated as high‑risk: Alcor vs EXTEX/SAP deadlines differ in operating‑hour thresholds and additional‑hours allowances. For Alcor, unknown hours are treated the same as 600+ hours and trigger a 50‑hour removal window or 15 June 2005, whichever is later. For EXTEX/SAP unknown hours are treated as 600+ and trigger a 100‑hour removal window or 15 June 2005. Operators who fail to investigate and resolve hours‑since‑new can unintentionally toggle into the shorter removal windows.

• Calendar dates embedded in the AD are historic: The AD references dates such as 15 June 2005 for removal windows for Alcor/EXTEX/SAP and a deadline of 1 March 2012 for replacement where RRC parts are not Rolls‑Royce manufactured, and 1 March 2017 as the latest date for RRC deferred replacement. When applying the AD now, operators should check whether their aircraft were compliant by the historic dates; however the AD text itself remains the legal instrument setting those dates as originally required. Confusion can arise when operators assume that because the AD became effective in 2012 some earlier dates no longer matter; the AD retains the historic deadlines for earlier cohorts and the RRC deferral dates.

• RRC deferred compliance is conditional and record‑dependent: The deferment applies only where multiple conditions are satisfied (acceptable power assurance checks; no recent chip lights or metal in oil; all mandatory RRC bulletins accomplished within designated compliance periods; maintenance records indicating proper OMM maintenance; compliance with CEB‑A‑1392 still applicable; parts related to the CEB/AD manufactured by Rolls‑Royce). This creates an evidentiary burden: lacking documented evidence, the operator cannot rely on the deferral. Maintenance records that are incomplete or ambiguous will force earlier replacement.

• Parts provenance matters to eligibility for deferral: If the parts related to the CEB or AD are not Rolls‑Royce manufactured, the RRC couplings must be replaced by the compliance date of revision 2 (1 March 2012). The supply chain traceability of parts thus directly affects whether an operator may continue to use an RRC coupling until next access. Operators who obtain third‑party or remanufactured parts without documenting provenance risk losing access to the deferral.

• Tight machining tolerances and ban on plating: The AD requires machining the impeller ID to produce an interference fit of 0.0000 to ‑0.0013 inch and expressly disallows plating of the impeller ID. Shops that rely on plating to restore worn impellers will find that option disallowed under the AD. Achieving and verifying the 0.0000 to ‑0.0013 inch interference fit requires accurate measurement and controlled thermal installation; improper work risks fretting or further failure. Measurement and machining precision standards thus matter operationally.

• Explicit prohibition against installing a -1 coupling into a used impeller: The AD states "Do not install a -1 coupling into a used impeller." That prohibition can catch maintenance personnel who might otherwise reuse -1 adaptors in older impellers. It also implies that close attention to dash sizes and prior part history is essential.

• New impeller required in some downgrades: The AD states that if a -3 coupling is removed then a new impeller is required. For an impeller already machined/fretted by earlier parts, substitution and re‑machining options are limited and may force purchase of a new impeller. That outcome impacts parts and labour costs materially.

• Heating procedure required per overhaul manual: The AD mandates heating per the engine overhaul manual to achieve the target fit during coupling installation. Shops must have and use the correct overhaul manual procedures; omission or incorrect heating during press fit installation could produce an out‑of‑tolerance interface.

• Fluorescent penetrant inspection mandated: Non‑destructive testing obligation is mandatory. Shops must include fluorescent penetrant inspection in their work cards and record results.

• "Next access" definition is strict: The AD defines "next access" as when the compressor module is separated from the engine and disassembled for any reason. Operational planning that delays compressor module separation will in effect delay the required replacement for eligible RRC couplings, but operators cannot claim continued operation if other AD conditions are not met. Misinterpreting "next access" as simply an inspection without module disassembly could result in non‑compliance.

• Compliance Code 4 not defined in the document: The AD lists "Compliance Code 4" but does not define it. Operators and engineers may be used to interpreting compliance codes via CASA material external to the AD; relying solely on the AD without checking CASA guidance on compliance codes can cause misclassification of urgency or process.

• Historic dates and amendment sequencing may create reading confusion: The AD states that if parts are not Rolls‑Royce manufactured, they must be replaced by the compliance date of revision 2 (1 March 2012), yet Amendment 3 becomes effective 8 March 2012. The chronology and multiple revisions can produce confusion about which compliance date applies to which cohort. Operators should track amendment revisions and the specific text for their engine/part scenario rather than applying an intuitive single date.

• The AD refers to other documents (RRC mandatory bulletins, CEB‑A‑1392, engine OMM) but does not reproduce their text: Compliance requires consulting, interpreting, and documenting compliance with external manufacturer documents. Misalignment between the AD and the content of those bulletins or potential later revisions of those bulletins can be a source of uncertainty.

These concrete particulars in the AD are the likely operational pitfalls. Risk mitigation requires explicit part‑tracking, clear recording of operating hours‑since‑new, traceability to parts‑manufacture provenance, careful machining to the stated tolerances, and documented fluorescent penetrant inspection and heating steps during installation.

This section converts the AD’s requirements into practical steps and checks that owners, operators and maintenance organisations should follow to comply with AD/AL 250/86 Amdt 3 as written in the source. The following steps follow directly from the AD text and its tables.

1. Inventory and identification

   • Review maintenance logs and parts records to identify whether any Rolls‑Royce 250‑B17 or C20 series engines in your fleet have compressor adaptor couplings listed in Table 1 (Alcor P/Ns 23039791AL and 23039791AL‑1/‑2/‑3; EXTEX P/Ns A23039791, E23039791, E23039791‑1/‑2/‑3, EH23039791, EH23039791‑1/‑2/‑3; RRC P/Ns 23039791‑1/‑2/‑3; SAP P/N A23039791). Table 2 lists typical airframes where the engines are installed but applicability is by engine and coupling P/N, not solely by airframe.

2. Determine operating hours‑since‑new and date applicability

   • For each affected coupling, determine the operating hours‑since‑new as of the AD’s effective date. The AD prescribes different removal windows depending on those hours:

     • Alcor: If 600+ hours or hours unknown, remove within 50 operating hours after the effective date or by 15 June 2005, whichever occurs later. If fewer than 600 hours on the effective date, remove before exceeding 650 hours or by 15 June 2005, whichever is later.
     • EXTEX and SAP: If 600+ hours or hours unknown, remove within 100 operating hours after the effective date or by 15 June 2005, whichever occurs later. If fewer than 600 hours, remove within 150 operating hours after the effective date or by 15 June 2005, whichever is later.
     • RRC: If seeking to use the deferred pathway, the coupling may remain until the next compressor module disassembly for any reason, but not later than 1 March 2017, provided the conditions in the AD are satisfied.

   • Where hours are unknown and cannot be determined, the AD treats them as if they are 600+ for the purposes of Alcor and EXTEX/SAP removals; document attempts to verify hours so the factual basis for compliance timing is clear.

3. Assess eligibility for RRC deferred compliance

   • If a coupling is an RRC coupling (P/N 23039791‑1/‑2/‑3) you may rely on the AD’s deferral to next access only if all the following conditions are demonstrably met at the time of assessment and continuing until next access: (a) The engine has been operating with acceptable power assurance checks. (b) The engine, gearbox, or turbine has not experienced any recent chip lights or metal‑in‑oil events. (c) All mandatory bulletins issued by RRC have been accomplished within their designated compliance requirements. (d) Maintenance records indicate proper engine maintenance has been performed per the applicable Operations and Maintenance Manual. (e) Compliance with Commercial Engine Bulletin (CEB)‑A‑1392 latest revision is still applicable next time the compressor is due for repair or overhaul. (f) Parts related to the CEB or AD have been manufactured by Rolls‑Royce. If they are not Rolls‑Royce manufactured, RRC couplings must be replaced by the compliance date of revision 2 (1 March 2012).

   • Document and retain evidence for each of the above conditions to support the deferral. If any condition cannot be satisfied, schedule removal per the earlier deadlines.

4. Plan maintenance scheduling and parts procurement

   • For couplings that must be removed within a short operating‑hour window, plan immediate maintenance slots and source the approved replacement P/Ns before removal. The AD prescribes approved replacement adaptors: P/Ns 23076559‑1, 23076559‑2, 23076559‑3, with adaptor outside diameters and target fits listed in Table 3.
   • If an impeller requires replacement (e.g. when a -3 coupling is removed), order a new impeller rather than attempting plating or reconditioning inconsistent with the AD’s prohibition on impeller ID plating.

5. Follow the AD’s machining and installation procedure

   • When replacing couplings, follow Requirement 4:
     • Select and measure the pilot OD of the new larger dash size coupling.
     • If a -1 coupling is removed, install a -2 coupling; if a -3 coupling is removed, install a new impeller (the AD gives the dash‑size example).
     • Machine the impeller ID to achieve an interference fit of 0.0000 to ‑0.0013 inch. After machining, the impeller must have no fretting.
     • Fluorescent penetrant inspect the impeller to detect cracks or defects.
     • Install a new compressor adaptor coupling, P/N 23076559‑2 or -3; if a new impeller is installed, use P/N 23076559‑1.
     • Heat the impeller per the engine overhaul manual to achieve the target fit specified in Table 3. Adaptor ODs and fits in Table 3:
       • 23076559‑1: OD 0.9000 to 0.9008 inch, fit 0.0000 to ‑0.0013 inch
       • 23076559‑2: OD 0.9020 to 0.9028 inch, fit 0.0000 to ‑0.0013 inch
       • 23076559‑3: OD 0.9040 to 0.9048 inch, fit 0.0000 to ‑0.0013 inch
     • Do not plate the impeller ID and do not install a -1 coupling into a used impeller.
     • Ensure that mating surfaces show no fretting prior to installation.

6. Non‑destructive testing and documentation

   • Conduct the fluorescent penetrant inspection and document the results, retaining the NDT reports with the engine maintenance records.
   • Record the new part numbers installed, measurement results, machining certificates, and the heating/installation procedures followed per the overhaul manual. Include traceability to part manufacture (important for RRC deferral conditions).

7. Coordinate with Rolls‑Royce bulletins and CEB‑A‑1392

   • Ensure all mandatory RRC bulletins are accomplished within their compliance windows and record that they have been completed. Confirm the status and applicability of CEB‑A‑1392 at the next compressor repair/overhaul event.

8. Use the AD’s definition of "next access" to plan work

   • For RRC coupling deferrals, remember "next access" is when the compressor module is separated and disassembled for any reason. When scheduling maintenance that requires such disassembly, include coupling replacement as part of the scope of work.

9. Maintain traceability and contemporaneous records at point of work

   • Keep records showing the date of removal/installation, the part numbers involved, hours‑since‑new at removal, measurements demonstrating the interference fit, NDT reports, and confirmation of compliance with RRC bulletins and the engine OMM where applicable.

10. Verify post‑installation serviceability

• After installation, confirm acceptable power assurance checks and monitor the engine for chip lights or metal in oil. Continued monitoring helps demonstrate that the AD remediation has been effective.

11. Consult CASA for interpretive questions and external compliance code meaning

• If there is ambiguity over the meaning of "Compliance Code 4" or other procedural matters the AD does not define, confirm with CASA or a nominated regulatory technical contact. The AD does not define enforcement procedures or that compliance code within its text.

12. Retain records for audit and for any future ADs or bulletins

• Given the AD’s linkage to mandatory RRC bulletins and CEBs, maintain records that may be reviewed by regulators or manufacturer representatives as evidence of compliance.

Following these steps implements the AD as written. The AD does not provide remedies for costs, nor does it define enforcement in this text; conformity is demonstrated through records and correct physical work documented against the AD’s requirements and the external RRC documents the AD references.