AD/PHZL/85 - Propeller Blade Thrust Bearing

This airworthiness directive is built around several technical and regulatory concepts that are important for operators and maintenance organisations to understand. The first is the formal definition of an “airworthiness directive” under Australian law. ADs are mandatory regulatory instruments issued by CASA under section 20C of the Civil Aviation Regulations 1988 (or the equivalent provisions in the Civil Aviation Safety Regulations 1998). They are used to correct an unsafe condition that is likely to exist or develop in aircraft, engines, propellers, or appliances. An AD overrides any routine maintenance schedule and must be complied with as a condition of maintaining the aircraft’s certificate of airworthiness. Non‑compliance can lead to enforcement action including suspension or cancellation of the certificate and civil penalties.

The second key concept is “time‑in‑service” (TIS). The AD uses this term in setting the compliance threshold. “Time‑in‑service” in the Australian regulatory context is defined as time from the moment an aircraft first moves under its own power for the purpose of flight until it comes to rest at the end of the flight, with engine(s) shut down. It is not the same as calendar months, which is the other trigger (nine months). The mixed time‑and‑event trigger means that a propeller that sees few hours each month may trigger on nine months even if 50 hours are not reached, whereas a high‑utilisation propeller may trigger much sooner on 50 hours. Additionally, the “next disassembled” trigger creates uncertainty because operators may have no immediate plan to disassemble the propeller; in that case they will be captured by the 50‑hour or nine‑month limit. The purpose of the disassembly trigger is to allow operators to combine the AD compliance with an already‑planned maintenance event to reduce incremental downtime, but it does not extend beyond the hard time limits.

The third concept is the “alert service bulletin” (ASB) and “service letter” as incorporated by reference. The AD does not repeat the detailed inspection procedures; it requires the operator to obtain and follow Hartzell’s ASB HD‑ASB‑61‑026 for bearing replacement and HD‑ASB‑61‑023 for the inspections. This is a common technique in aircraft regulation to avoid re‑specifying proprietary engineering data, but it means the operator must have access to the latest FAA‑approved revisions of those documents. The AD language “or later FAA approved revisions” is important: it allows the manufacturer to update the procedures without re‑issuing the AD, but it also means the operator must check whether later revisions exist and whether they have been approved by the FAA. The FAA’s approval is automatically accepted as equivalent to CASA approval for these service bulletins, but that acceptance is contingent on CASA’s reliance on the FAA’s type certification basis.

The fourth concept is “eddy current inspection” (ECI), a non‑destructive testing method that detects surface and near‑surface cracks in conductive materials. ECI on the propeller hub requires specialised equipment and trained personnel. Unlike a simple visual inspection, ECI is sensitive to operator technique, probe calibration, and surface condition. The AD requires both a 10X magnification‑assisted visual inspection and an ECI; these are complementary because visual inspection can pick up larger cracks or surface flaws that might not be detectable by ECI (e.g., if the crack is filled with debris), while ECI can find fine or hidden cracks not visible to the naked eye.

Finally, the AD introduces the concept of a “serviceable hub”. A hub found cracked must be removed before further flight and replaced with a hub that has been inspected and found serviceable. The AD does not provide instructions for repairing a cracked hub; the only remedy is replacement. This implies that a cracked hub is considered beyond economical repair for continued use on the propeller. The cracked hub may be returnable to the manufacturer for evaluation, but the AD imposes no such requirement; the operator’s duty ends with removal and replacement.

The AD applies directly to any person or organisation in Australia that owns, operates, or maintains a Hartzell HD‑E6C‑3( ) propeller installed on an aircraft on the Australian register. The applicability paragraph notes that these propellers are installed on, but not limited to, Fairchild Dornier 328‑100 series aeroplanes. This means the AD also potentially covers other aircraft types that use the same propeller model. The use of parentheses in the model designation (“HD‑E6C‑3( )”) indicates that the basic model may have optional suffixes such as letters that vary the blade configuration, but the AD applies regardless of whether such suffixes are present.

The primary affected parties are the registered operators of those aircraft. For a Fairchild Dornier 328‑100, this might be a regional airline, a commuter carrier, a charter operator, a freight operator, or a private owner. The cost burden falls directly on the operator, as the AD requires them to arrange and pay for the replacement bearings, inspections, and any necessary hub replacement. There is no government subsidy or compensation. Operators must ensure their maintenance providers are approved to perform the work, which adds another layer of cost and coordination.

Secondary affected parties include Approved Maintenance Organisations (AMOs), Licensed Aircraft Maintenance Engineers (LAMEs), and any repair station that services Hartzell propellers. These entities must have the correct equipment for eddy current inspection and personnel trained in the Hartzell service bulletin procedures. They must also maintain up‑to‑date copies of the service bulletins and any revisions. If the propeller must be removed and sent off‑wing to a specialist propeller shop, that adds shipping time and cost. If the aircraft is flown to a different base for the AD work, that flight itself burns time‑in‑service that may bring the compliance deadline closer.

The AD also affects Hartzell Propeller Inc. indirectly, in that it creates demand for the new design bearing part number C‑7438 and potentially reduces demand for the older bearing part numbers. However, the AD also imposes liability risk on Hartzell if subsequent failures occur despite compliance. The AD cross‑references the FAA’s investigation into the cause of the thrust bearing failures, which is described as “yet to be determined” in the background. This is an important distinction: the AD is based on an observed statistical failure rate, not a fully understood root cause. That means a more fundamental redesign or additional inspections may follow in future ADs if the root cause is identified later.

Aircraft insurers may also be affected indirectly. An operator that fails to comply with the AD may find its insurance policy voided for breach of statutory or regulatory requirements, particularly if a subsequent accident is linked to the unresolved bearing issue. Conversely, compliance with the AD may have been a condition of coverage already. The AD creates a bright‑line compliance event: after 19 January 2006, any aircraft with the old design bearings is technically unairworthy, and operating it may expose the operator to regulatory enforcement and potential liability.

Finally, the AD affects future buyers and sellers of affected aircraft. The compliance history of the AD becomes a material fact in any sale. A propeller that has not had the bearings replaced and inspections completed will likely require a substantial discount to reflect the immediate cost of compliance or, if the AD is overdue, the risk of enforcement action. Conversely, a fully‑compliant propeller is a marketable advantage.

The AD imposes several clear duties on the registered operator of the aircraft, but it also includes important rights and options for compliance.

The primary duty is to accomplish the mandatory actions by the specified compliance times. For requirements 1, 2 and 3, the duty arises at the earliest of: 50 hours time‑in‑service after the effective date, nine calendar months after the effective date, or when the propeller is next disassembled after the effective date. The duty is not optional; it arises automatically upon the occurrence of the first trigger event. For requirement 4 (removal of cracked hub), the duty arises before further flight after discovery of a crack during either inspection. For requirement 5 (prohibition on installation of old bearings), the duty arises immediately after the effective date and continues indefinitely.

A related duty is to maintain accurate records of compliance. The regulations require that each AD action be entered in the aircraft’s maintenance records, including the date, hours TIS, the inspector’s identification, and references to the service bulletins used. This record becomes the evidence of compliance if CASA conducts an audit or ramp check. Without proper documentation, the operator may be treated as non‑compliant even if the work was actually performed.

The AD also confers a right to use alternative methods of compliance, but only with CASA approval. The AD includes a note that references FAA AD 2002‑22‑08, and it is common for Australian ADs to allow operators to apply for an alternative method of compliance (AMOC). An operator who believes that a different inspection technique or a different bearing part number could achieve an equivalent level of safety may submit a proposal to CASA. However, the AD does not spell out the AMOC procedure; it must be done in accordance with regulations or with CASA policy. Obtaining an AMOC is a formal process that requires engineering justification and likely takes weeks or months. For practical purposes, most operators will follow the prescribed Hartzell instructions.

The operator also has a right to delegate the physical work to a qualified maintenance organisation. The AD does not require the operator to perform any of the work personally. The operator can contract with an AMO or a LAME who holds an appropriate approval for propeller maintenance. However, the operator remains ultimately responsible for ensuring compliance. This is a significant practical point: if the maintenance organisation makes an error (e.g., fails to perform the ECI correctly), the operator bears the regulatory risk.

Another right is the ability to combine the AD action with other scheduled maintenance, taking advantage of the “when the propeller is next disassembled” trigger, as long as that event occurs before the 50‑hour or nine‑month limit. This allows the operator to reduce incremental downtime by, for example, performing the AD work during an engine overhaul or a routine propeller inspection. The risk is that the operator may assume the propeller will be disassembled within nine months, but if that maintenance event is delayed beyond the other trigger, the hard deadlines take over and the aircraft may become non‑compliant without warning.

An important right implicit in the AD is the right to operate the aircraft up until the exact moment the trigger event occurs. There is no requirement to accomplish the work early. An operator can legally fly the aircraft until it reaches 50 hours TIS or nine months from the effective date, whichever comes first. However, this creates a compliance cliff edge. If the operator misjudges the application of the triggers (for example, by misunderstanding what constitutes “next disassembled” for a propeller that is removed for reasons other than maintenance, such as for storage or shipping), they may inadvertently become non‑compliant.

Finally, the AD confers no right to compensation from the regulator for the cost of compliance. An AD is a mandatory safety directive; operators bear the economic burden as part of operating an aircraft in Australia. This is consistent with the general principle that airworthiness is a condition of the privilege of flying, not a right that the state must subsidise.

Non‑compliance with this AD constitutes a breach of the Civil Aviation Act 1988 and the regulations made under it. Specifically, operating an aircraft that does not meet the applicable airworthiness directives is a criminal offence or may attract civil penalties depending on the circumstances. The maximum penalties for an individual can include imprisonment for up to two years and/or fines up to several thousand penalty units. For a body corporate, fines can be substantially higher. The exact penalty amount depends on the number of penalty units then prescribed under the Crimes Act 1914 for regulatory offences. At the time of the AD’s issue (2005), a penalty unit was $110; under current law it is $313. The court also has discretion to impose other sanctions, such as ordering the operator to pay the costs of the prosecution.

Enforcement is typically initiated by CASA, which may conduct audits, ramp checks, or investigate reports of non‑compliance. If CASA finds a propeller with the old design bearing P/N C‑2882‑1, C‑2882‑2, or C‑7075 installed after the effective date, that is an immediate finding of non‑compliance with requirement 5. Similarly, if a hub crack was noted during an inspection not conducted within the compliance timeframe, the operator may be found to have violated requirements 2 and 3.

Beyond criminal penalties, CASA has administrative enforcement tools. It can issue a direction to the operator to ground the aircraft until the AD is complied with. It can also suspend or cancel the aircraft’s certificate of airworthiness. If the aircraft remains airborne while non‑compliant, CASA can pursue a civil penalty for each day of operation. The Civil Aviation Safety Regulations 1998 (as amended from time to time) provide for infringement notices (on‑the‑spot fines) for less serious breaches, but a deliberate failure to comply with a safety‑critical AD would likely be treated as a serious matter and referred for prosecution.

The AD itself contains no separate penalty schedule; its legal force comes from the parent Act. The AD also imposes no obligation to report findings of cracks or bearing failures to CASA, but such findings may be reportable under other regulations, such as the requirement to report defects that could endanger the aircraft. Reporting a crack during the AD inspection may trigger an alert to the manufacturer and to the FAA, potentially leading to further AD action. However, the AD does not create a separate reporting duty.

An important practical penalty is the effect on the aircraft’s insurance. Most aviation insurance policies require the aircraft to be maintained in an airworthy condition and in compliance with all applicable ADs. Failure to comply with this AD could give the insurer grounds to deny coverage for any claim arising from a subsequent incident, even if the incident was unrelated to the propeller. In extreme cases, the insurer may repudiate the policy retrospectively, leaving the operator uninsured for past operations.

Finally, non‑compliance can have reputational consequences. In a small aviation community, news of an AD compliance failure can spread quickly. Maintenance organisations may refuse future work from an operator known to be lax on ADs. The operator’s safety culture may be questioned by regulators and the public. These indirect penalties, while not codified, can be commercially significant.

This AD operates within a dense network of domestic and international regulatory instruments. Domestically, it derives its authority from the Civil Aviation Act 1988 and the Civil Aviation Regulations 1988 (CAR 1988) or the Civil Aviation Safety Regulations 1998 (CASR 1998), depending on the certification regime for the aircraft in question. For a Fairchild Dornier 328‑100, which is a large foreign‑type‑certificated aeroplane, the applicable regulations are likely to be CASR Part 21 (Certification of aircraft) and Part 42 (Continuing airworthiness). The AD is a mandatory continuing airworthiness requirement.

The AD expressly cross‑references FAA AD 2002‑22‑08, Amdt 39‑12933. This signifies that the underlying unsafe condition was originally identified by the FAA, and the FAA issued its own AD for aircraft on the US register. The Australian AD effectively adopts the same corrective actions but re‑issues them under Australian law. This is a common practice under the Bilateral Aviation Safety Agreement between Australia and the United States, which allows each country to accept the other’s ADs without re‑investigation. However, the Australian AD may have different wording or compliance times due to differences in the fleet or the regulatory framework. In this case, the compliance time mirrors the FAA’s but is expressed in hours TIS and calendar months, consistent with Australian practice.

The AD also incorporates by reference two Hartzell service bulletins: HD‑ASB‑61‑026 and HD‑ASB‑61‑023. These documents are part of the manufacturer’s maintenance instructions and are considered “approved data” for the purpose of the AD. Using a service bulletin revision that has not been approved by the FAA (and implicitly by CASA) would mean the work does not comply with the AD. Operators must therefore be careful to use only the exact revision specified or a later FAA‑approved revision.

The interaction with other ADs is important. If the propeller has multiple ADs, the operator must comply with all of them. There may be ADs for the same propeller model addressing different issues (e.g., AD for blade de‑icing, AD for hub corrosion). Each AD is independent; compliance with this one does not relieve compliance with another. The operator’s maintenance program must schedule all applicable ADs.

The AD also interacts with the aircraft’s approved maintenance program (AMP). The AMP may include scheduled tasks for the propeller, such as overhauls at specified intervals. The “when the propeller is next disassembled” trigger in this AD may coincide with a scheduled overhaul, but if the overhaul interval is longer than nine months, the AD will force an unscheduled disassembly. This could disrupt the AMP and require special approval from CASA if the AMP is based on a flying program. Some operators may seek a variation to the AMP to align the AD with an existing event, but that variation itself requires CASA acceptance.

Finally, the AD interacts with international obligations. Australia is a state of design and state of registry under the Chicago Convention. When CASA issues an AD based on an FAA directive, it is discharging its obligation to ensure that aircraft on its register maintain a level of safety equivalent to that required by the state of design (the United States). If a foreign operator operates an Australian‑registered aircraft of this type, it must still comply with Australian ADs even if the aircraft is in another country.

The source document provided is the original issuance of AD/PHZL/85, effective 19 January 2006. There is no indication within the text of any previous amendments to this AD. The AD number “PHZL/85” and “1/2006” suggest it is the first version of this particular directive issued in 2006. The background notes that the FAA issued its AD (2002‑22‑08) in 2002, and Hartzell issued service bulletins in May and August 2001, so the Australian AD was issued several years after the FAA action. The delay may reflect CASA’s workload, the need to confirm that the same unsafe condition existed in the Australian fleet, or the time required to document the AD in the domestic format.

There is no published amendment history for this AD in the extracted text. However, in the normal course, an AD may be amended if later information reveals the need for different compliance times, additional inspections, or an expanded applicability. For example, if Hartzell later determined that the root cause of the bearing fractures was related to a specific batch of bearings, CASA might amend the AD to exempt certain serial numbers. Alternatively, if the new design bearing C‑7438 itself developed problems, a superseding AD could replace this one. No such events are reflected in the source.

The incorporation of “or later FAA approved revisions” in the AD means that the service bulletins themselves may be revised without amending the AD. This is not an amendment of the AD, but it effectively changes the required procedures for those who use later revisions. Operators must be proactive in checking whether later revisions exist. CASA may also issue an alternative method of compliance (AMOC) that effectively modifies the AD for a particular operator, but that is not a formal amendment to the AD numbering.

It is worth noting that ADs are serialised. If this AD is superseded, the new AD would have a different number (e.g., AD/PHZL/85/1 or a new year designation). The text does not indicate any supersession.

The source document does not mention any litigation history for this AD. Airworthiness directives are rarely challenged in Australian courts. The legal basis for issuing an AD is well established in the Civil Aviation Act, and courts give considerable deference to CASA’s safety determinations. An AD is a legislative instrument, and a challenge would require an applicant to show that the decision to issue the AD was legally unreasonable or that the procedure was not followed. Given that the AD mirrors an FAA directive and is based on specific engineering investigation and reported failures, it would be very difficult to mount a successful legal challenge.

It is possible that a maintenance organisation or operator affected by the AD could seek judicial review on procedural grounds (e.g., that CASA did not consult adequately), but the Act does not require prior consultation before issuing an urgent AD. The Civil Aviation Regulations allow CASA to issue an AD without providing an opportunity for comment if the unsafe condition requires immediate action. Given the failures described in the background and the FAA’s prior action, this AD could be classified as urgent.

Another potential source of litigation is a dispute over liability after an accident involving the propeller. If an operator complied with the AD but a bearing or hub failed anyway, the operator might sue Hartzell for product defect. The AD’s background states that the cause of the bearing fractures “has yet to be determined”, which could be used by a plaintiff to argue that the manufacturer had not done enough to identify and fix the true cause. Conversely, the manufacturer could argue that it had taken prudent interim action by developing a new design bearing. Any such litigation would be in the realm of product liability and tort, not administrative law.

There is no evidence in the source of any public court case specifically citing AD/PHZL/85. Given the age of the AD (2005/2006), the Fairchild Dornier 328‑100 fleet in Australia is likely very small, possibly with only a small number of aircraft. The economic stakes may be too low to justify litigation. Additionally, most AD compliance is handled through the maintenance system without legal dispute.

For the purpose of this deep dive, we can only state that there is no litigation history mentioned in the source. That does not mean no legal proceedings exist, but we cannot invent them. In practice, ADs are almost always complied with without challenge, and any disputes are resolved informally with CASA.

The AD contains several traps for the unwary operator. The first is the ambiguity of “when the propeller is next disassembled after the effective date of this AD”. The term “disassembled” is not defined. Does it mean any removal of the propeller from the aircraft, or only a full disassembly of the hub? If the propeller is removed for a routine inspection but the hub is not disassembled, does that trigger the requirement? The safer interpretation is that the trigger is the point at which the hub would be opened for any purpose, because only then can the bearing replacement and inspections be performed efficiently. However, an operator who removes the propeller for storage without disassembling the hub may argue that the trigger was not activated. The AD does not resolve this, so the operator should err on the side of caution and treat any propeller removal as a trigger event.

The second gotcha is the “whichever occurs first” clause. This is a race between three independent triggers. An operator who plans to comply at the next scheduled overhaul six months from the effective date (which is within nine months) must also check whether the propeller will accumulate 50 hours before that overhaul. If the aircraft flies 80 hours per month, the 50‑hour trigger will fire in less than a month, much earlier than the planned maintenance. The operator must track hours accurately and not rely on the calendar alone.

The third gotcha is the requirement “before further flight after the effective date of this AD” for requirement 4. This means that if a hub crack is discovered at any time (including during the required inspections, but also during unrelated maintenance), the aircraft may not be flown again until a serviceable hub is installed. This could ground the aircraft for days or weeks if spare hubs are not immediately available. The operator should have a contingency plan for sourcing a serviceable hub, either from stock, from another operator, or from Hartzell.

The fourth gotcha is the grandfathering provision. It states that propellers that had the replacement done using Hartzell ASB HD‑ASB‑61‑026 dated 6 August 2001, or Service Letter HD‑SL‑61‑034 dated 7 May 2001, are considered compliant with requirement 1. However, those earlier documents may not have included the same inspection procedures (visual and ECI) that the AD now requires. Grandfathering only applies to requirement 1 (bearing replacement). The inspections (requirements 2 and 3) still need to be performed within the compliance time, even if the bearings were replaced years ago. An operator who was proud of having done the bearing replacement early may overlook the inspection requirement and be non‑compliant.

The fifth gotcha is the application to all Hartzell HD‑E6C‑3( ) propellers, regardless of the suffix letters. The note says “the parentheses indicate the presence or absence of an additional letter(s) which vary the basic propeller blade model designation. This AD still applies regardless of whether these letters are present or absent.” This means that an operator cannot rely on a slightly different model designation to argue the AD does not apply. If the basic model matches, the AD applies.

The sixth gotcha is that the AD does not explicitly require a final record of compliance to be sent to CASA. The operator only needs to have the records available for inspection. This creates a risk that an operator does the work but does not document it adequately. If CASA conducts a ramp check and the logbook entry is missing key information (e.g., the revision of the service bulletin used), the operator may be cited for non‑compliance even though the physical work was done.

The seventh gotcha is the cost of the eddy current inspection. Many small AMOs do not have ECI equipment or personnel qualified to perform it. The operator may have to send the propeller to a specialised shop, incurring shipping and turnaround time. The nine‑month trigger may seem generous, but if the propeller must be removed and sent away, the aircraft may be grounded for the entire time, affecting revenue.

Finally, the AD’s background notes that the cause of the bearing fractures “has yet to be determined”. This means the AD is a stop‑gap measure, not a final fix. The operator should remain alert for future ADs that may require additional actions once the root cause is found. The investment in compliance now may not be the end of the matter.

Compliance with AD/PHZL/85 requires a systematic approach. The first step is to confirm applicability. The operator must identify whether the aircraft has a Hartzell model HD‑E6C‑3( ) propeller. The AD applies regardless of the suffix letters in the model designation. If the aircraft is a Fairchild Dornier 328‑100 series, it is very likely applicable, but the operator should verify the propeller model number on the data plate or maintenance records. If the propeller model does not match, the AD does not apply, but the operator should still note the possibility of other ADs for the same propeller.

The second step is to determine the compliance status. Check whether the propeller has already had its blade thrust bearings replaced with P/N C‑7438 using Hartzell ASB HD‑ASB‑61‑026 (6 August 2001) or Service Letter HD‑SL‑61‑034 (7 May 2001). If so, requirement 1 is satisfied, but requirements 2 and 3 (visual and ECI inspections) must still be performed. If the replacement was done but not using those specific documents, the replacement does not satisfy the AD and must be repeated. If the bearings have not been replaced, all three requirements must be accomplished.

The third step is to obtain the required documents. The operator or the maintenance organisation must have copies of:

• Hartzell Alert Service Bulletin HD‑ASB‑61‑026 (original dated 6 August 2001 or later FAA‑approved revision).
• Hartzell Alert Service Bulletin HD‑ASB‑61‑023, Revision 1, dated 23 May 2001 (or later FAA‑approved revision).

These are proprietary documents available from Hartzell Propeller Inc. The operator should ensure they have the latest revision and confirm FAA approval. CASA does not supply these bulletins; they must be obtained commercially.

The fourth step is to schedule the work, taking into account the compliance triggers. The work must be completed by the earliest of: 50 hours TIS after 19 January 2006, 9 months after 19 January 2006 (i.e., by 19 October 2006), or when the propeller is next disassembled after 19 January 2006. The operator should track TIS accurately. If the aircraft is due for any maintenance that involves propeller removal or disassembly before those dates, the AD work should be combined with that event. The operator should also plan for the possible need to replace the hub (requirement 4) and have a replacement hub available or a plan to obtain one quickly to avoid an extended grounding.

The fifth step is to perform the work in accordance with the service bulletins. For requirement 1, the old bearings (P/N C‑2882‑1, C‑2882‑2, C‑7075) must be removed and replaced with P/N C‑7438. For requirement 2, a visual inspection of the propeller hub using 10X magnification must be performed, following the bulletin instructions. For requirement 3, an eddy current inspection of the hub must be performed. Both inspections must be done even if no cracks are expected.

The sixth step is to handle any cracks found. If a crack is found in the hub, the hub must be removed from service before further flight (requirement 4). The aircraft may not be flown until a serviceable hub is installed. The cracked hub should be quarantined and may be returned to Hartzell for investigation, but the AD does not mandate this.

The seventh step is to document compliance. The operator must ensure the following entries are made in the aircraft’s maintenance records:

• The date of compliance.
• The aircraft and propeller identification.
• The AD reference (AD/PHZL/85).
• A statement that requirements 1 through 5 have been complied with (or specific notes for exceptions).
• The part numbers of bearings installed.
• The results of the visual and eddy current inspections.
• The serial number of the new hub if replacement was required.
• The signature and licence number of the certifying engineer.
• A reference to the service bulletin revisions used.

These records must be retained for the life of the aircraft or as required by regulations.

The eighth step is to ensure that no old‑design bearings are installed after the effective date. Requirement 5 prohibits installation of P/N C‑2882‑1, C‑2882‑2, or C‑7075 into any HD‑E6C‑3( ) propeller. This applies to any maintenance or repair, not just the initial compliance. If the propeller is later disassembled for other reasons, the operator must not re‑install old bearings. Only P/N C‑7438 or later approved parts may be used.

The ninth step is to monitor for future revisions. The AD allows use of “later FAA approved revisions” of the service bulletins. If Hartzell issues a revision after the AD is in effect, the operator should check if it is FAA‑approved. Using a later revision may be optional, but if it provides clearer instructions or addresses additional inspection points, it is advisable. The operator should also watch for superseding ADs or additional AD actions.

Finally, the operator should consider filing a voluntary report if any anomalous findings are made during the inspections, such as multiple cracked hubs or unusual bearing wear. While not required by this AD, reporting under the mandatory defect reporting scheme may help the regulator and manufacturer improve safety.

Compliance with this AD is a condition of the aircraft’s certificate of airworthiness. The costs and effort of compliance are a normal part of operating a fleet, and the penalties for non‑compliance are severe. A methodical approach as outlined above will ensure the operator meets the legal obligations and keeps the aircraft in service.