AD/PR/33 Amdt 3 - Hub Assembly

Airworthiness Directive (AD). An AD is a legally enforceable notification issued by CASA under the Civil Aviation Safety Regulations. It mandates inspection, modification, or operational restriction on aircraft or components when an unsafe condition is identified. Non-compliance with an AD is a breach of Australian air law and can ground the aircraft, attract civil penalties, or lead to criminal prosecution. AD/PR/33 Amdt 3 is one such directive, specific to a family of Dowty propeller hubs.

Hub assembly. The directive applies to propellers fitted with hub part numbers 660714241 or 660714255. The hub is the central structural component of the variable-pitch propeller. It houses the pitch-change mechanism and transmits engine torque to the blades. Failure of the hub can result in blade liberation and consequent loss of aircraft control. The AD uses the term “hub” to refer to this component, not the propeller blades or the spinner.

Non-Destructive Testing (NDT). The AD requires NDT checks for cracks in the hub rear half wall. NDT refers to inspection techniques that do not damage the component being examined. Dowty’s ASB SF340-61-95 describes a method that is “convenient for aircraft operators to perform,” in contrast to the B-scan method in the component maintenance manual, which typically requires specialised facilities and is done only at overhaul. The AD thus brings crack detection into the line maintenance environment.

Alert Service Bulletin (ASB) versus Service Bulletin (SB). An ASB denotes a manufacturer-issued bulletin of higher urgency, often addressing a safety hazard. Dowty ASB SF340-61-95 is the inspection procedure that the AD mandates. A standard SB (in this case SB SF340-61-105) is a modification bulletin; the AD recognises its accomplishment as terminating action, ending the need for further repetitive inspections.

Terminating action. This is a modification or replacement that eliminates the root cause of the unsafe condition, making ongoing inspections unnecessary. In this AD, the terminating action is modifying the propeller per Dowty SB SF340-61-105 at any revision. Once that modification is done, the operator is no longer bound by the repetitive inspection requirement. Replacement of a cracked hub with a new serviceable unit does not constitute terminating action, because the new unit is of the same design and remains at risk of cracking.

Compliance intervals. The first inspection must be accomplished within 1,200 flight hours after 24 February 2000, which was the effective date of the original AD. For any hub that entered service after that date, or for an aircraft imported into Australia later, the initial compliance point is ambiguous on the face of the directive. The AD does not provide a clean start date for hubs that were not in service on 24 February 2000. Repetitive inspections thereafter must occur at intervals not exceeding 1,200 flight hours from the previous inspection.

Supersedure. The AD explicitly supersedes UK CAA AD 006-10-99, meaning the earlier UK directive is no longer in force in Australia. Operators who complied with the UK AD prior to the Australian AD’s effective date gain credit for those inspections if they were done per the ASB at original issue or Revisions 1 through 4. After the effective date, only Revision 5 of the ASB is acceptable for initial or subsequent inspections.

CASA Delegation. The directive is signed by a delegate of CASA. Delegates have statutory authority to issue ADs under Part 39 of the Civil Aviation Safety Regulations.

The directive imposes duties on a narrow but identifiable set of parties.

Aircraft operators. The primary duty holders are operators of Saab SF340A and 340B aircraft, because that is the type known to be fitted with the affected propellers: Dowty Aerospace Propellers Models R389/4-123-F/25, R389/4-123-F/26, and R390/4-123-F/27, with hub part numbers 660714241 or 660714255. The directive applies regardless of whether the aircraft is on the Australian register, operated under an Australian air operator certificate, or flown into Australian territory. It does not capture other aircraft types using the same propeller models unless they also have the specific hub part numbers. Each operator must identify whether its fleet includes these hubs and, if so, manage the inspection cycle.

Maintenance organisations. Approved maintenance organisations (CASR Part 145) and licensed aircraft maintenance engineers (LAMEs) who perform the NDT checks must be familiar with Dowty ASB SF340-61-95 Revision 5. The directive does not require that the NDT be performed by the operator itself, but the operator bears ultimate responsibility for compliance. Maintenance providers must produce inspection reports that contain the data required by paragraph 2.B of the ASB, and they must forward those reports to Dowty within 30 days.

Dowty Propellers (now part of GE Aviation). Dowty is not a duty holder under the AD but is the recipient of the inspection reports and the source of the service documents. The AD makes Dowty the custodian of the inspection data, which it presumably uses to track fleet-wide crack occurrences. Dowty also controls the revision status of the ASB and SB; later approved revisions are automatically accepted for compliance without further CASA action.

Manufacturers and modifiers. Any entity that modifies the propeller hub per Dowty SB SF340-61-105 brings the aircraft out of the repetitive inspection population. This may include propeller overhaul shops or modification centres authorised by Dowty.

Insurers and lessors. While not directly named, insurers of Saab aircraft will likely incorporate compliance with CASA ADs into policy conditions. Lessors may require evidence of AD compliance in lease agreements. Non-compliance can affect the airworthiness certificate and therefore the insurability and lease continuity of the asset.

Passengers and third parties. The background notes that failure of the hub could cause the propeller to detach, leading to loss of control. The directive thus indirectly protects persons on board the aircraft and persons or property on the ground. However, the AD imposes no rights or duties on them directly.

Duty to inspect. Each operator must perform an NDT inspection of the propeller hub rear half wall as per Dowty ASB SF340-61-95 Revision 5. The initial inspection must be done within 1,200 flight hours after 24 February 2000. Thereafter, inspections must be repeated at intervals not exceeding 1,200 flight hours. The duty applies to every hub that remains unmodified per SB SF340-61-105.

Duty to submit inspection reports. Within 30 days after each inspection, the operator must send an inspection report to Dowty Propellers in accordance with paragraph 2.B of the ASB. The report presumably includes identification data, inspection results, and any findings. The AD does not specify penalties for late reporting, but failure to comply with any requirement of the AD is a breach.

Duty to replace cracked hubs. If a crack is found during any required inspection, the hub must be replaced with a serviceable unit before further flight. This grounds the aircraft immediately if no replacement hub is available. Replacement does not stop the repetitive inspection cycle because the new hub is of the same design and must be inspected within the next 1,200 flight hours or at the due date of the next inspection, whichever is later (assuming the compliance clock resets with replacement, but the AD is silent on that point).

Right to use prior credit. Inspections accomplished before the effective date of Amdt 3 (12 March 2009) in accordance with earlier revisions of the ASB (original issue, Rev 1, 2, 3, or 4) are recognised as meeting the initial requirement. Those inspections do not need to be redone per Rev 5 unless the repetitive interval has expired.

Right to use later approved revisions. The AD states that “the use of later approved revisions of these documents is acceptable for compliance.” This allows Dowty to publish Rev 6 or later without requiring a new AD. However, the operator must ascertain that the revision is “approved” by Dowty and that it is indeed later than Rev 5. The AD does not define “approved” but presumably means formally published by Dowty.

Right to terminate repetitive inspections. Accomplishing the modification per Dowty SB SF340-61-105 (any revision) ends the obligation to perform the repetitive NDT checks. This is the only terminating action recognised. An operator that chooses to modify all affected propellers can then cease the 1,200 flight hour cycle.

No right to alternative methods of compliance. The directive does not contain a clause allowing CASA to approve alternative methods of compliance (AMOCs). Operators cannot substitute a different NDT method or a different interval unless Dowty revises the ASB and that revision is “later approved.” This is a stricter approach than some ADs that permit operator-submitted AMOCs.

The directive itself does not prescribe penalty amounts, but it is issued under Part 39 of the Civil Aviation Safety Regulations (CASR). Non-compliance with an AD is a breach of CASR 39.001 and related provisions. Under the Civil Aviation Act 1988, the maximum penalty for an individual who contravenes a provision of the regulations can be up to 50 penalty units (currently $313 per unit as of 2023, but subject to indexation) and for a body corporate up to 250 penalty units per day the offence continues. Criminal prosecution is possible if the breach is knowing or reckless.

Enforcement mechanisms available to CASA. CASA can direct the operator to ground the aircraft until compliance is demonstrated. It can suspend or cancel the aircraft’s certificate of airworthiness. It can issue a written direction to cease operations. It can also impose a civil penalty by application to a court. In practice, CASA may first issue a warning or a notice of proposed enforcement action. The AD does not create any private right of action for damages; enforcement is solely through CASA’s regulatory powers.

Grounding risk. The most immediate penalty for a crack found during inspection is grounding: the directive says “replace the hub … before further flight.” If a serviceable hub is not available, the aircraft remains grounded until a hub can be sourced, which imposes direct economic loss on the operator. There is no grace period.

Self-reporting. While the directive requires sending an inspection report to Dowty within 30 days, it does not expressly require reporting to CASA. However, if a crack is found and the aircraft is grounded, the operator would typically need to notify CASA to vary its airworthiness status. Failure to comply with the reporting duty (to Dowty) is itself a breach of the AD.

Insurance implications. Non-compliance with an AD may void hull and liability insurance policies, as most aviation insurance policies require the aircraft to be maintained in accordance with all applicable airworthiness directives. An operator that attempts to fly after a crack is found or without performing the inspection on time risks having a claim denied.

Global reciprocity. EASA AD 2009-0005 refers to the same unsafe condition. Violation of the Australian AD may have no direct extraterritorial effect, but the European Union Aviation Safety Agency and other national authorities may take independent enforcement action against operators or aircraft that subsequently enter their jurisdiction.

CASR Part 39 - Airworthiness Directives. AD/PR/33 Amdt 3 is issued under Part 39. Part 39 governs the issuance, amendment, and revocation of ADs in Australia. The directive itself does not restate the procedures of Part 39; it is the product of that regulation. Compliance with the AD is compliance with Part 39.

Other ADs. The directive supersedes UK CAA AD 006-10-99 within Australia. For operators who relied on the UK AD before the Australian AD came into effect, the supersedure means they must now follow the Australian AD. The directive also references EASA AD 2009-0005, issued on 8 January 2009. That EASA AD may impose equivalent or slightly different requirements in Europe. An operator with aircraft that fly to Europe would need to comply with both the Australian AD and the EASA AD, which may not be identical in compliance times or methods. The Australian AD does not deem compliance with the EASA AD as compliance with its own requirements.

CASR Part 42 - Continuing Airworthiness Requirements. The operator of an Australian registered aircraft has a general duty under Part 42 to ensure the aircraft is maintained in an airworthy condition. Compliance with all applicable ADs is part of that duty. The directive thus plugs into the broader continuing airworthiness management system.

CASR Part 145 - Approved Maintenance Organisations. If the NDT inspection is performed by a Part 145 organisation, that organisation must hold appropriate ratings for the propeller and for NDT methods. The directive does not alter Part 145 requirements but adds a specific task that must be documented and certified.

Private contracts. Leases, charter agreements, and aircraft management contracts often require compliance with all ADs. A breach of this AD could put the operator in breach of contract. Conversely, a lessor may require that the terminating action (SB SF340-61-105) be accomplished as a condition of lease, because it eliminates the repetitive inspection burden and reduces future maintenance expense.

Australian Consumer Law and the Civil Aviation Act. The directive does not create any consumer rights. It is a safety regulation, not a product liability institution. However, if a hub fails despite compliance with the AD, the operator may have claims against Dowty under contract or tort law. The AD itself does not affect those rights.

International standards. The International Civil Aviation Organization (ICAO) requires state signatories to ensure that aircraft on their register comply with airworthiness directives issued by the state of design. Since the propellers are of UK design (Dowty Rotol), the Australian AD is consistent with ICAO Annex 8 obligations. The reference to EASA AD indicates coordination among national authorities.

The directive has passed through five formal stages: the original issue and three numbered amendments, with an implicit later amendment that added the terminating action and Rev 5.

Original issue (24 February 2000). CASA (then the Civil Aviation Safety Authority) first adopted the UK CAA AD 006-10-99 as AD/PR/33. The original AD mandated NDT inspections of the Dowty R389/4 and R390/4 propeller hubs using the then-current version of Dowty ASB SF340-61-95. The initial compliance interval was 1,600 flight hours.

Amendment 1 (effective 28 December 2000). This amendment extended the compliance interval for the initial inspection and the repetitive interval from 1,600 to 1,800 flight hours. The reason is not stated in the background of the current AD, but presumably CASA determined that a longer interval still provided an adequate level of safety. Amendment 1 also may have updated the ASB revision required, but the background is silent.

Amendment 2 (effective 23 January 2003). Amendment 2 reversed course and reduced the compliance intervals from 1,800 back to 1,200 flight hours. The background of Amdt 3 explains that the reduction was needed. Dowty had revised the ASB in January 2008 (between Amdt 2 and Amdt 3) to update and improve the inspection methods.

Amendment 3 (effective 12 March 2009). This is the current directive. It made several changes: (1) it updated the required version of the ASB to Revision 5; (2) it added a provision that inspections done before the effective date in accordance with earlier revisions of the ASB are acceptable for the initial compliance; (3) it introduced terminating action via Dowty SB SF340-61-105 (any revision); (4) it consolidated the earlier amendments and formally superseded UK CAA AD 006-10-99; (5) it retained the 1,200 flight hour repetitive interval.

Subsequent amendments. No further amendments are mentioned in the source. However, the AD allows use of later approved revisions of the ASB. If Dowty issued Revision 6 or later, operators may use it without a new AD. That effectively gives Dowty the power to change the inspection method without CASA amending the AD.

The amendment history illustrates a pattern of trial and error with the compliance interval: first set at 1,600 FH, then increased to 1,800 FH, then reduced to 1,200 FH, where it has remained. These changes impose retrospective compliance burdens on operators who may have planned maintenance schedules around earlier intervals.

No litigation specifically concerning AD/PR/33 Amdt 3 or the underlying unsafe condition is mentioned in the source text. Given the highly technical and prescriptive nature of airworthiness directives, they are rarely challenged directly in court. Challenges would most likely occur in the context of an enforcement action by CASA, where an operator contests a penalty or grounding order on the grounds that the AD was invalidly issued or that compliance was impossible. No such case is known to be reported in Australian aviation law journals.

Potential grounds for litigation might include: whether CASA properly followed Part 39 procedures when issuing the AD; whether the AD is technically feasible given the availability of the ASB and Rev 5; or whether the operator had a valid defence of impossibility if a replacement hub were unobtainable. The directive itself contains no carve-out for unavailability of parts, so an operator forced to ground an aircraft for lack of a serviceable hub might face commercial pressure but would have limited legal recourse.

Separately, if a hub failed despite the inspection regime, civil tort claims against Dowty or CASA could arise, but the directive itself would not be the subject of that litigation. The existence of the AD could be used as evidence of the standard of care owed by the operator, but it is not a cause of action.

There is also no record of judicial review proceedings regarding the earlier amendments (Amdt 1 or Amdt 2). It appears that operators accepted the changes without court challenge. The high cost of litigating against a regulator and the relatively small population of affected aircraft (only Saab 340 operators) likely make litigation uneconomic.

Thus, for practical purposes, the litigation history is a blank slate. The directive operates in a regulatory environment where compliance is the norm and enforcement is administrative rather than judicial.

Ambiguous initial compliance date for later entrants. The directive says the initial inspection must be done “within 1,200 FH after 24 February 2000.” That date is the effective date of the original AD, not Amdt 3. For an aircraft that first entered service in Australia in 2005, or a hub that was replaced in 2008, the 1,200 hour clock already ran out long ago. The directive does not say “within 1,200 FH of the hub first being installed on an Australian aircraft” or “within 1,200 FH of this amendment becoming effective.” A strict reading would require that all hubs, regardless of when they entered service, have already passed the initial deadline. A reasonable operator would interpret the requirement as “within 1,200 FH of the first inspection after the hub becomes subject to the AD,” but the text does not say that. This creates legal uncertainty and could catch out an operator who relies on a common-sense reading.

Replacement does not reset the clock. If a hub is replaced due to a crack, the new hub must be inspected at the next due interval. But does the interval restart from zero for the new hub, or must the new hub be inspected at the time the old hub’s next inspection was due? The AD says “replacement of the hub does not constitute terminating action for the repetitive inspection requirements.” It does not explicitly say the new hub gets its own 1,200 hour cycle. In practice, most operators would treat the new hub as a new component that requires an initial inspection within 1,200 FH of its installation, but the AD is silent. An overzealous regulator could argue that the clock continues from the original hub.

Terminating action is mandatory only if chosen. The AD does not require operators to accomplish the terminating action; it merely offers it as a way to end repetitive inspections. Operators who do not modify per SB SF340-61-105 are locked into perpetual 1,200 hour inspections. Over the life of an aircraft, the cumulative cost of these inspections may far exceed the cost of the modification. The AD does not provide a time limit by which the terminating action must be taken; operators may postpone indefinitely.

Reporting to Dowty within 30 days is a separate obligation. The inspection itself is the main duty, but the reporting deadline is tight. If a maintenance organisation performs the inspection but takes 30 days to send the report, and the report is sent on day 31, the operator is in breach even if the inspection was perfect. The AD does not allow extensions.

No AMOC provision. Unlike many ADs that allow operators to propose alternative methods of compliance for CASA approval, this AD contains no such clause. The only flexibility is through later revisions of the ASB. If an operator wants to use a different NDT method or a different interval, it has no path unless Dowty publishes a revision. This is a significant compliance rigidly.

Cost of parts and downtime. The AD does not address the economic impact. A serviceable replacement hub may be scarce, and lead times could be months. The grounding requirement creates immediate financial loss. Operators should stockpile hubs or arrange pooling agreements. The AD does not mandate that Dowty maintain a supply of hubs.

Recordkeeping burden. While not explicit, operators must maintain records of each inspection, the report sent to Dowty, and any replacements. These records must be retained for the life of the component. A lost report could be treated as non-compliance.

Compliance is a multi-step process that should be integrated into the operator’s continuing airworthiness management system. The following steps assume the operator has identified that it operates affected propellers.

1. Identify affected components. Check each aircraft’s propeller for model number (R389/4-123-F/25, /26, or R390/4-123-F/27) and hub part number (660714241 or 660714255). Also check for hubs that were reworked per drawing 660714259; those remain affected. Note that the propeller may be installed on Saab SF340A or 340B, but the AD applies to the propeller model itself, not the aircraft type. Any propeller meeting the model and hub part number is affected regardless of what aircraft it is on.

2. Determine compliance status. For each hub, determine the date of the last NDT inspection performed under the original AD or amendments. If an inspection was done before 12 March 2009 in accordance with Dowty ASB SF340-61-95 at original issue or Rev 1-4, that counts as an initial inspection. The next inspection is due at the later of: (a) 1,200 flight hours after 24 February 2000, or (b) 1,200 flight hours after the last inspection. If the last inspection was after 12 March 2009, it must have been performed per Rev 5. If not, a new inspection per Rev 5 is needed now.

3. Obtain the current required documents. Dowty ASB SF340-61-95 Revision 5 is mandatory for all inspections after 12 March 2009. Obtain a copy from Dowty. Also obtain Dowty SB SF340-61-105 if terminating action is planned. Monitor Dowty’s service bulletins for later approved revisions of the ASB; using those is acceptable and may contain improved methods.

4. Schedule the inspection. The NDT check must be accomplished within the applicable flight hour interval. Since the original date (24 Feb 2000) is long past, all hubs are likely overdue unless they have been continuously inspected every 1,200 FH. Use the aircraft’s maintenance planning system to track each hub’s hours. Inspections should be performed at a suitable facility with access to the required NDT equipment and personnel trained in the ASB methods.

5. Perform NDT in strict accordance with Rev 5. Follow every step in the ASB. The directive does not allow substitution of equivalent methods. Document the results.

6. Prepare and send the inspection report within 30 days. Follow paragraph 2.B of the ASB for data content. Send to Dowty Propellers at the address specified in the ASB. Retain a copy of the report in the aircraft maintenance records.

7. If a crack is found, replace the hub before further flight. The aircraft is grounded until a serviceable hub (new or overhauled with no cracks) is installed. There is no grace period. After replacement, the new hub must be inspected at the next scheduled interval; treat it as a continuing component subject to the same AD.

8. Consider terminating action. Evaluate the cost of performing Dowty SB SF340-61-105 versus continuing perpetual 1,200 hour inspections. The modification will likely require propeller removal and shop work. Once accomplished, the repetitive inspection requirement ceases. Keep evidence of modification (e.g., work order, logbook entry citing the SB and revision) in the aircraft record.

9. Maintain a compliance log. For each propeller, maintain a record of: hub serial number, date and FH of each inspection, revision of ASB used, date of report sent to Dowty, any cracks found, any replacements, and date of terminating action if taken. This log demonstrates compliance during a CASA audit or during insurance inquiries.

10. Review the AD upon each aircraft maintenance cycle. If Dowty releases a later revision of the ASB, determine whether it supersedes Rev 5 and update procedures accordingly. The AD’s acceptance of later approved revisions means the operator must stay current. Revisions may change inspection methods or intervals, so do not assume Rev 5 is the last word.