AD/CRESCO/10 - MLG Axles

The AD rests on several technical and regulatory concepts. Main landing gear (MLG) axle refers to the component that supports the wheel assembly on the aircraft’s main landing gear strut. In the Cresco 08-600, the MLG axle is a structural part that endures high cyclic loads during take-off, landing, and ground manoeuvring on agricultural strips. The AD identifies three part numbers: 08-40021-1 (the original, now discontinued), 08-40021-2 (a replacement introduced by MOD PAC/CR/0442), and 08-40021-3 (a further replacement introduced by MOD PAC/CR/0443, with a different inspection requirement). These P/Ns are the key basis for which inspection regime applies.

Magnetic particle inspection is a non-destructive testing method used to detect surface and slightly subsurface discontinuities in ferromagnetic materials. The AD requires an approved method equivalent to ASTM Standard No. E-1444, which establishes minimum requirements for magnetic particle examination. Note 4 of the AD explains that this method detects cracks and other flaws that are not visible to the naked eye. For axle P/N 08-40021-3, the AD substitutes dye penetrant inspection, a different NDT method that uses a liquid penetrant to reveal surface-breaking cracks. The change implies that the material or geometry of axle P/N 08-40021-3 makes magnetic particle inspection inappropriate or less effective, or that the manufacturer chose a simpler method.

Time in service and landings are the two metrics that trigger compliance. Time in service means the number of hours the aircraft has been flown since the axle was new or since last inspection. Landings count each take-off and landing cycle, which correlates with stress cycles on the axle. The AD uses whichever threshold occurs first to ensure safety regardless of usage pattern; but for the first magnetic particle inspection on P/N 08-40021-1, it uses “whichever occurs later” to allow a grace period for aircraft close to the threshold at the effective date.

Torque plates are components that ensure correct tightening of axle nuts and maintain proper preload. The AD mandates that torque plates P/N 08-40055-2 and 08-40056-2 be fitted when axles P/N 08-40021-2 or 08-40021-3 are installed. This is a design improvement introduced with the newer axles.

Restricted category agricultural operations limits the applicability of the AD. The Cresco 08-600 was certified in the restricted category for agricultural use (crop dusting, spraying), which under the Civil Aviation Safety Regulations allows certain operational flexibility but also imposes specific maintenance and airworthiness controls. The AD only applies to aircraft operating in that category; if a Cresco 08-600 is used for other purposes (e.g., cargo or passenger carrying), it might be on a different type certificate or standard category, and thus not subject to this directive - but such use is highly unlikely given the aircraft’s design.

The concept of approved direct or indirect magnetic particle inspection method requires reference to the maintenance manual and service letter. The AD does not itself specify the detailed technique but relies on the PAC Cresco 08-600 MM and Supplement PAC/CR/0442 for instructions. This incorporation by reference means operators must have access to the current versions of those documents. Similarly, the visual inspection instructions in Table 1 and Table 2 of PACSL/CR/06-1 Revision 1 guide what to look for at shoulder radii.

Finally, the effective date of 15 February 2007 creates a hard deadline. Most compliance actions are measured from that date, so aircraft with high hours or landings may need immediate action. The AD includes “unless already accomplished within the last [X] hours” provisions to avoid duplicate work, but operators must prove compliance by logbook entries.

The primary population affected is every owner and operator of a Pacific Aerospace Corporation Cresco 08-600 aeroplane that is operated in the restricted category for agricultural purposes and that has MLG axles with part numbers 08-40021-1, 08-40021-2, or 08-40021-3. Given that the Cresco 08-600 is a dedicated agricultural aircraft (a crop-dusting variant of the PAC 750XL), the entire active fleet within Australia is likely captured. The number of aircraft is small - probably fewer than fifty - but each represents a significant capital investment for a farming or spraying business. The AD therefore affects a niche but high-value segment of general aviation.

Beyond the operator, the AD directly impacts approved maintenance organisations (AMOs) and licensed aircraft maintenance engineers (LAMEs) who perform the inspections. They must have the necessary equipment: magnetic particle inspection rigs, dye penetrant kits, and training to interpret results per ASTM E-1444. If an AMO does not have in-house NDT capability, they must subcontract to a specialist, incurring cost and scheduling delay. The AD also requires disassembly and reassembly of the MLG wheel assembly, which is labour-intensive.

Parts suppliers and manufacturers are affected because the AD creates ongoing demand for replacement axles and torque plates. The original P/N 08-40021-1 is discontinued, so operators must upgrade to P/N 08-40021-2 or 08-40021-3, which may require ordering from Pacific Aerospace Corporation or approved distributors. The mandatory torque plate fitting for those axles adds a further parts cost.

Insurance companies that underwrite hull and liability policies for agricultural aviation may impose compliance with all applicable ADs as a condition of coverage. Non-compliance could void coverage in the event of an accident. Thus insurers indirectly enforce the AD.

Pilots and ground crews are affected by increased downtime. The inspection intervals, particularly the 150-hour security and visual checks, require frequent removal of the wheel assembly. That means the aircraft is out of service for a period - potentially a day or more - during peak spraying season. For an operator with a single Cresco, this could mean lost revenue from missed contracts. For multi-aircraft operations, it forces scheduling of inspections to minimise grounding of the entire fleet.

The AD does not apply to Cresco 08-600 aircraft not operated in the restricted category (if any exist) or to other Cresco models or other PAC aircraft. It also does not apply to aircraft with MLG axles of different part numbers (e.g., those already upgraded to a later revision not covered). However, the wording “fitted with MLG axles part number (P/N) 08-40021-1, 08-40021-2, or 08-40021-3” is inclusive of all three; any aircraft with at least one of those axles on either main gear is affected. If a mixed installation exists (different left and right), the AD must be satisfied for each axle individually.

The background notes that there is a “known history of cracking” - that suggests previous service bulletins or earlier ADs have addressed this issue. Operators who have already complied with earlier requirements (e.g., PAC SL/CR/99-2 or PACSL/CR/06-1) must still comply with this AD, but the initial compliance intervals may be different if that work was recent. The AD’s “unless already accomplished” provisions help avoid redundant re-inspection, but only if the earlier work was done within the specified past hours/landings.

The duty for the operator or owner of an affected aircraft is set out in the “Requirement” and “Compliance” sections. At its core, the duty is to inspect MLG axles at prescribed intervals using specified methods, and to replace cracked axles before further flight. The duty attaches to the aircraft, not the person, meaning the aircraft cannot be operated unless the AD is complied with; but it is the registered operator who is legally responsible under regulation 39.2 of the Civil Aviation Safety Regulations (making it an offence to operate an aircraft not in compliance with an applicable AD).

The duties are not monolithic; they differentiate by axle P/N. For axles P/N 08-40021-1 and -2, the operator must: disassemble the MLG wheel assembly; inspect for security; visually inspect for cracks (focusing on shoulder radii per the service letter); and perform magnetic particle inspection using a method equivalent to ASTM E-1444. For P/N 08-40021-3, the NDT method is dye penetrant instead. In all cases, cracked axles must be replaced before further flight. After inspection, the axle must be re-assembled and lubricated per the maintenance manual.

In addition, the AD creates a duty to fit specific torque plates (P/N 08-40055-2 and 08-40056-2) when axles P/N 08-40021-2 or -21-3 are installed. This is mandatory and effectively means that if you install one of those axles (either as a replacement or if originally fitted), you must install the torque plates. Failure to do so would mean the aircraft is not in compliance with the AD.

The duties extend to record-keeping. The AD does not explicitly state it, but compliance must be evidenced in the aircraft’s maintenance records (logbook) showing the date, hours and landings, method used, and any findings. This is implicit in the maintenance regulations (Part 43 of CASR) which require documentation of AD compliance.

The rights of the operator are limited but real. Under the AD, they may choose which inspection method to use for magnetic particle inspection, as long as it is approved and equivalent to ASTM E-1444. They may also choose to replace an axle with a different P/N (e.g., upgrade from 08-40021-1 to 08-40021-3) to alter the inspection regime. For example, the dye penetrant inspection for P/N 08-40021-3 has a first inspection interval of 50,000 landings, which is far more generous than the 6,000-landing magnetic particle inspection for P/N 08-40021-1 or -2. However, the upgrade requires fitting torque plates and likely a modification approval (it references MOD PAC/CR/0443). But the AD itself does not prohibit such a change; it merely prescribes what must be done if those axles are installed. The operator also has the right to rely on previous inspections done within the allowed look-back periods to avoid starting the cycle anew (e.g., if the security inspection was done 100 hours ago, it is deemed current for the first compliance).

The operator has no right to extend inspection intervals or substitute a different method without further approval from CASA. The AD is mandatory; any deviation would require a non-compliance report and possibly a special approval under regulation 39.3 (alternative means of compliance). There is no explicit right of appeal in the AD itself, but general administrative law applies.

The AD does not state penalties; its legal force derives from the Civil Aviation Safety Regulations 1998 (CASR), Part 39, which empowers CASA to issue airworthiness directives with binding effect. Regulation 39.2 makes it an offence to operate an aircraft in contravention of an applicable AD. The maximum penalty under the Civil Aviation Act 1988 for such an offence can be substantial - for an individual, a fine of up to 50 penalty units (currently about $13,000) and for a body corporate up to 250 penalty units (currently about $65,000), with higher penalties possible if the contravention causes danger to life or property (section 20AA). Additionally, CASA can suspend or cancel the aircraft’s certificate of airworthiness, effectively grounding the aircraft until compliance is demonstrated.

Enforcement is typically carried out through routine surveillance by CASA inspectors or by approved organisations’ audits. An AMO performing maintenance on a Cresco 08-600 must confirm AD compliance before releasing the aircraft. If an inspector finds non-compliance during a ramp check or during an investigation after an incident, the operator faces enforcement action. CASA may issue a warning letter, a direction to ground, or commence prosecution.

Civil liability may also arise: if a cracked axle fails due to non-compliance and causes damage or injury, the operator could face civil tort claims, and the insurer might deny coverage on the basis of regulatory non-compliance.

The AD includes a reference to the New Zealand CAA AD DCA/CRESCO/10, indicating that a similar directive is in force in New Zealand. An Australian operator operating in New Zealand airspace would also need to comply with the NZ AD; conversely, a NZ operator operating in Australia would need to comply with this AD. Non-compliance in Australia could affect the aircraft’s ability to operate under bilateral agreements.

The background statement about a known history of cracking means CASA could point to prior service letters as notice that the risk was known. An operator who ignores the AD does so with clear awareness of the danger, which could increase the severity of penalties if an accident occurs.

Enforcement also extends to maintenance personnel. If an engineer falsely certifies compliance (e.g., claims a magnetic particle inspection was done when it was not), they could be in breach of CASR Part 43 and face loss of licence, fines, or criminal prosecution for forgery or fraud. The AD’s specificity about methods (ASTM E-1444, reference to specific manual pages) makes it hard to claim ignorance; the requirements are concrete and verifiable.

AD/CRESCO/10 is a legislative instrument made under the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations 1998. It operates within that hierarchy: it has the force of law for the aircraft types and parts it specifies, and aircraft must be maintained in accordance with all applicable ADs. It interacts primarily with CASR Part 39 (Airworthiness Directives), which sets out the legal framework for making, amending, and complying with ADs. Part 39 requires that no person operate an aircraft unless each applicable AD is complied with; it also permits alternative means of compliance if approved by CASA.

The AD incorporates by reference several documents: the PAC Cresco 08-600 Maintenance Manual (MM) (Chapters 05, 12, 32), PACSL/CR/06-1 Revision 1 (the service letter), and ASTM Standard No. E-1444 (for magnetic particle inspection). These documents are not reproduced in the AD; the operator must obtain and follow the current versions. The AD also references MOD PAC/CR/0442 and PAC/CR/0443 - these are manufacturer modifications that introduce the newer axles and the torque plate requirements. Failure to adhere to the incorporated documents is a failure to comply with the AD.

The AD interacts with CASR Part 43 (General maintenance rules), which governs how maintenance is performed, documented, and certified. The disassembly, inspection, and reassembly described in the AD must be performed by a person authorised under Part 43 (e.g., a LAME or an AMO with appropriate ratings). The magnetic particle or dye penetrant inspection must be carried out by a person with the requisite NDT certification (likely in accordance with CASR Part 66 or the relevant standards). The maintenance manual chapters referenced form part of the approved data for the aircraft type, so deviation from those instructions would also breach Part 43.

It interacts with CASR Part 145 (Approved Maintenance Organisations) if the work is done by an AMO. The AMO must have the equipment, training, and procedures to execute the specific NDT methods. If the AMO does not have magnetic particle inspection capability, they must subcontract to a suitably approved facility. The AD does not require the work to be done by an AMO; a private owner could do the work if they hold the appropriate licence ratings, but in practice the complexity and need for NDT equipment make AMO involvement likely.

The AD references the New Zealand CAA AD DCA/CRESCO/10, indicating that CASA and NZ CAA have coordinated the directive. For a dual-registered aircraft or one moving between countries, compliance with one AD will typically satisfy the other if the requirements are identical. However, if the NZ AD differs in intervals or method, the aircraft would need to meet the stricter standard.

The AD does not explicitly interact with occupational health and safety laws, but the disassembly and NDT work would need to follow safe work practices. Nor does it interact with environmental laws, except in the disposal of any cracked axle (treated as scrap metal). It also does not interact with the Competition and Consumer Act; operators cannot seek compensation from the manufacturer for the cost of compliance unless a separate defect claim exists.

Attorney-client privilege may arise if legal advice is sought regarding the scope of the AD or potential non-compliance. But that is general law, not specific to this AD.

The source document is AD/CRESCO/10, issued 5 January 2007, effective 15 February 2007. There is no amendment history provided within the source text itself, but we can infer its place in a series. The AD number “AD/CRESCO/10” suggests it is the tenth AD issued for the Cresco series aircraft. The notation “2/2007” indicates it is the second AD published in 2007 (the numbering convention may be internal to CASA).

The AD explicitly replaces or supersedes prior maintenance requirements. It references PAC SL/CR/99-2 - a service letter from 1999 that previously addressed MLG axle cracking. The background notes that during a scheduled 500 hour inspection, a crack was detected and confirmed using inspection per that service letter. This suggests that SL/CR/99-2 was the previous standard, but it was likely an advisory document. This AD makes compliance mandatory.

The AD also incorporates PACSL/CR/06-1 Revision 1, a service letter dated sometime in 2006 (and revised). This service letter updates the visual inspection instructions and provides Tables 1 and 2 for crack locations. The AD makes this service letter mandatory - earlier versions were likely advisory.

The notes in the AD explain that MOD PAC/CR/0442 introduced axles P/N 08-40021-2 as a replacement for the discontinued P/N 08-40021-1, and MOD PAC/CR/0443 introduced axles P/N 08-40021-3 with a dye penetrant inspection requirement. These modifications were approved by the manufacturer and presumably by CASA or NZ CAA before the AD was issued. The AD therefore consolidates the mandatory inspection requirements for all three axle variants, harmonising the compliance intervals and methods.

The AD lists torque plates P/N 08-40055-2 and 08-40056-2 as mandatory when -2 or -3 axles are installed. This requirement may be new; earlier installations of -2 or -3 axles might have been done without those torque plates if no AD then existed. This AD retroactively requires their fitting.

Since this AD was issued in 2007, over 16 years ago, it may have been superseded or amended by later directives. The source text does not indicate any subsequent amendments, but it is common for ADs on high-time components to be revised to reflect accumulated service experience, changes in maintenance manuals, or availability of new parts. For example, a later AD might extend intervals if cracking proves rare, or shorten them if failures increase. The absence of amendment history in the source means we cannot provide details; a reader should check the current CASA AD database for any later revisions.

The AD also cross-references the NZ CAA AD DCA/CRESCO/10, suggesting that the NZ version may have an independent amendment history. Australia and New Zealand have a mutual recognition agreement for ADs, but amendments in one country may be adopted by the other with a lag.

The source text contains no mention of any litigation, challenges, appeals, or court cases related to AD/CRESCO/10. Airworthiness directives are legislative instruments issued by a delegate of the Director of Aviation Safety. They are subject to judicial review under the Administrative Decisions (Judicial Review) Act 1977 (ADJR Act) or the common law. However, challenges are rare because the instruments are based on safety considerations and courts give substantial deference to the regulator’s technical expertise.

A dissatisfied operator could theoretically challenge the validity of an AD on the grounds that it was beyond power, procedurally unfair, or irrational. To succeed, they would need to show that no reasonable decision-maker could have concluded the safety risk warranted the directive. Given the known history of cracking (stated in the background), such a challenge would be difficult. There is no public record of a case specific to AD/CRESCO/10, but general aviation AD cases exist (e.g., related to engine ADs) and have consistently been upheld.

Another possible avenue is a challenge to the incorporation of documents by reference (the maintenance manual sections, service letter, ASTM standard). If those documents are not readily accessible, an operator could argue lack of proper notice. But CASA typically makes such documents available through the manufacturer or via its website.

No evidence in the public domain suggests litigation arising from non-compliance with this AD either. Any enforcement action by CASA would normally result in an infringement notice or a prosecution in a magistrate’s court; such matters are not widely reported. If a crack resulted in an accident, the downstream litigation would likely involve product liability claims against Pacific Aerospace Corporation or negligence claims against the operator for failing to comply, rather than challenges to the AD.

The AD’s reference to the New Zealand CAA version suggests possible cross-border enforcement issues, but that would be handled under bilateral aviation safety agreements, not local litigation.

Overall, the litigation history for this AD appears to be nil. That is consistent with most ADs: they are complied with or result in administrative penalties, not courtroom battles. The costs of challenging a safety directive (legal fees, grounding uncertainty) usually outweigh the potential benefit, given that operators are highly risk-averse.

Several subtle aspects of AD/CRESCO/10 could catch out an unwary operator or maintainer.

Applicability limited to restricted category agricultural operations. The AD says it applies to “All Cresco 08-600 aircraft on restricted category agricultural operations.” If an operator uses a Cresco for non-agricultural work (e.g., surveying, training, or freight), it might not be on a restricted category certificate. However, practically all Cresco 08-600 aircraft were certified in the restricted category for agricultural use, so this limitation may be moot. But an operator who has converted the aircraft to the standard category for other purposes would not be subject to this AD - but then they would likely be operating under a different type certificate and maintenance schedule anyway. Still, the wording is a trap: if the aircraft logbook says “restricted category” but it is used for agricultural ops, the AD applies.

Whichever occurs first vs. whichever occurs later. Most compliance thresholds use “whichever occurs first” to ensure early action. But for the first magnetic particle inspection of P/N 08-40021-1, the AD says “whichever occurs later” when comparing 500 hours, 6,000 landings, and 150 hours after effective date. This unusual phrasing gives the operator the longest possible grace period among those three thresholds. If an aircraft already has 600 hours and 7,000 landings at the effective date, it would not need to comply until 500 hours from effective date? No: it says “within 150 hours time in service after 15 February 2007” combined with “whichever occurs later”. So for an aircraft already over 500 hours and 6,000 landings, the later event would be 150 hours after 15 Feb (the effective date). So the first inspection is required by 150 hours TIS after 15 Feb 2007. That could be a short timeframe if the aircraft flies a lot.

The “unless already accomplished” provisions. For security and visual inspections, the AD says “unless already accomplished within the last 150 hours time in service” (or 300 hours for visual). That look-back period is measured from the effective date, not from the current date. So an operator who did the inspection 140 hours before 15 February 2007 would be compliant for the initial interval. But if the last inspection was 160 hours before, they must redo it. The look-back periods differ (150 hours for security, 300 for visual). This is easy to misapply.

Inspection intervals track both hours and landings, but they differ for each inspection type. Security inspections repeat at 150 hours or 1,500 landings. Visual inspections at 300 hours or 3,000 landings. Magnetic particle for -1 at 500 hours or 6,000 landings. For -2 magnetic particle at 6,000 landings (no hours). For -3 dye penetrant first at 50,000 landings then every 6,000 landings. The operator must track both metrics and comply with whichever threshold comes first for each inspection. This creates multiple compliance calendars on the same component.

Torque plates are mandatory but only with -2 and -3 axles. If an aircraft already has -2 or -3 axles installed at the effective date, the torque plates must be retrofitted immediately. The AD does not specify a grace period for the torque plate fitment. It simply states “are to be fitted when MLG axles P/N 08-40021-2 or 08-40021-3 are installed.” This means that a -2 or -3 axle installed before 15 Feb 2007 without torque plates must be brought into compliance. That may require a trip to the hangar.

The ASTM E-1444 standard is not reproduced. Operators must have access to the standard or use an equivalent method approved by the manufacturer or CASA. Using a non-equivalent method is non-compliance. The AD does not list approved methods; it only says “equivalent to ASTM E-1444”. This leaves room for argument. A smart operator will document which method was used and how equivalence was determined.

Mixed axle part numbers. An aircraft might have a -1 axle on one side and a -2 on the other. The AD applies to both. The compliance schedule must be tracked separately for each axle. The torque plate requirement applies only to the side with the -2 or -3 axle.

New axles reset the landing count? The AD says “on the MLG axles” - for initial compliance, the interval is based on the total time/landings accrued on those specific axles, not the aircraft. If a new axle is installed, the count starts from zero. But the inspection method is tied to the P/N.

Maintenance manual edition. The AD references “PAC Cresco 08-600 Maintenance Manual (MM)” without specifying revision. The operator must ensure they use the current revision at the time of inspection. If the manual has been amended since the AD was issued, the AD still applies but the detailed instructions may have changed.

Inspection includes shoulder radii only? The visual inspection must pay attention to shoulder radii as per tables in the service letter. That implies other surfaces may not need visual inspection, but the magnetic particle inspection should cover the entire axle. A lazy inspector might only look at the radii and miss cracks elsewhere.

The AD is not a one-off; it is recurring. Operators must set up a recurring task card in their maintenance system. The first compliance may be disruptive because it may require immediate work, but the ongoing burden is manageable if tracked.

Finally, the AD may be superseded. A diligent operator should check whether a later AD, amendment, or alternative means of compliance has been issued since 2007. The source document is from 2007, and there may be newer data extending intervals or changing methods.

Compliance with AD/CRESCO/10 requires a systematic approach. The following steps are a practical guide for the operator or AMO.

Step 1: Determine applicability. Confirm that the aircraft is a Cresco 08-600 operated in the restricted category for agricultural operations. Check the aircraft’s type certificate and maintenance records. Then identify the P/N of each MLG axle installed. This will require reference to the aircraft parts catalogue or logbook. If the P/N is one of the three listed, the AD applies. If the P/N is different, the AD may not apply, but record why.

Step 2: Establish baseline compliance status relative to 15 February 2007. The initial compliance dates depend on hours and landings accrued on those specific axles as of the effective date. For each axle, calculate:

• Total time in service (airframe or axle hours).
• Total landings (including the landing during which a crack might have occurred). Then apply the “unless already accomplished” look-back provisions. For example, if a security inspection (step a) was done within the last 150 hours of time in service before 15 Feb 2007, it is current; otherwise, schedule it before the cumulative limit (150 hours after 15 Feb, or 1,500 landings from the axle’s start). The same logic applies to visual and NDT.

Step 3: Organise the work. The AD requires disassembly of the MLG wheel assembly. Ensure the AMO has the proper tools and the current revision of PAC Cresco 08-600 MM Chapters 32 and 12, as well as PACSL/CR/06-1 Revision 1, and the specific supplement (PAC/CR/0442 or PAC/CR/0443) for the axle P/N. Also obtain the ASTM E-1444 standard or an equivalent approved method.

Step 4: Perform inspections in order. Sequence (a) security inspection per Chapter 05-10-00 page 615. This checks axle security, likely torque and fasteners. Then (b) visual inspection per the service letter tables for the specific P/N. Focus on shoulder radii as directed. Then (c) NDT: magnetic particle for -1 and -2 axles; dye penetrant for -3 axles. Record any findings. If cracks are detected, replace the axle before further flight. Use only approved replacement parts (the current P/N, with torque plates for -2 and -3). After replacement, reassemble and lubricate per MM Chapters 32 and 12.

Step 5: Torque plate compliance. If the aircraft has -2 or -3 axles, verify that torque plates P/N 08-40055-2 and 08-40056-2 are installed. If not, install them. This is a one-time requirement; thereafter they remain with the axle.

Step 6: Document all actions in the aircraft maintenance logbook. Enter the date, aircraft hours/landings at compliance, the axle P/N, the inspection method used, any cracked findings and replacements, and the next due intervals. Use a maintenance schedule system to track the recurring intervals (e.g., a 150-hour/1,500-landing calendar for security, etc.). Track landings separately from hours; many agricultural strips result in high landing counts.

Step 7: Plan for ongoing compliance. Set up reminders in the maintenance program. Since intervals differ, a single spreadsheet or maintenance tracking software should calculate due dates based on whichever threshold occurs first. Note that the NDT intervals for -1 and -2 are based on landings (6,000) with no hour limit, so if the aircraft flies low and slow with many short flights, landings will be the limiting factor. For -3, the first dye penetrant is at 50,000 landings - a very high threshold - then repeats at 6,000 landings.

Step 8: Monitor for updates. Check the CASA website for any amended or superseding ADs. If the manufacturer issues a new service letter or if the maintenance manual is revised, the AD remains in force but the detailed instructions may change. Ensure the AMO is using current data.

Step 9: If facing operational difficulties, consider alternative means of compliance. Under CASR Part 39, an operator may apply to CASA for approval of an alternative method if it provides an equivalent level of safety. For example, extending an interval based on fleet data or using an ultrasound method instead of magnetic particle. This is a formal process requiring evidence and likely delays.

Step 10: Budget for costs. Over 16 years of adherence, the costs accumulate. Each inspection cycle requires labour (disassembly, cleaning, NDT, reassembly), possibly replacement parts if cracks found, and aircraft downtime. For a typical Cresco flying 200 hours per year with, say, 500 landings, the security inspection would be needed roughly every 9 months (150 hours) or 3 years (1,500 landings) whichever first. The magnetic particle for -1 would be needed every 2.5 years (500 hours) or 12 years (6,000 landings) - but the hours limit will dominate. For -2, only landings matter: 6,000 landings might take many years. For -3, the first dye penetrant at 50,000 landings may never be reached in the aircraft’s lifespan. So the compliance burden depends on the axle P/N and usage pattern. Operators with -1 axles face the most frequent NDT. Upgrading to -3 axles, even at the cost of torque plates, could drastically reduce inspection frequency - a rational cost-benefit decision.