AD/PHS/18 Amdt 4 - Hub Cracking

Hub retaining nut torque check. This is the primary mechanical measure. The directive requires the operator to verify that the torque on the propeller hub retaining nuts falls within the limits specified in the latest applicable Hamilton Sundstrand MM. The check is not a one‑off; it must be repeated every 500 flight hours. If the torque values are not acceptable, the propeller is unairworthy and must be removed from service. The concept of “acceptance criteria” is defined solely by reference to the manufacturer’s maintenance manual, which means the operator must have the correct revision of that manual and apply it without deviation.

Fluorescent penetrant inspection (FPI) of dowel pin holes. This is a non‑destructive testing method used to detect surface‑breaking cracks. The directive requires this inspection concurrently with the removal of any propeller for unacceptable torque values. If crack indications are found, the propeller hub must be removed from service. The directive notes that this method is “prescribed” in the applicable Hamilton Sundstrand MM, so the operator must follow the manufacturer’s FPI procedure exactly, including any required cleaning, application of penetrant, dwell time, developer, and inspection under UV light.

One‑time loosening and re‑tightening. This is an unusual feature. If the initial torque check passes, the operator must still loosen and then re‑tighten the hub retaining nuts using the procedure in the MM. This is a proactive step intended to ensure the nuts have been correctly torqued from a “fresh” baseline, addressing the fretting problem identified in the background. The loosening and tightening only has to be done once, and the torque values must be recorded in the propeller maintenance records as a one‑time entry. Subsequent torque checks (every 500 hours) do not require loosening and re‑tightening unless the propeller is newly installed.

Oil leakage inspection and investigation. Every 70 flight hours the operator must visually inspect for any external oil leakage. If leakage is observed, an investigation must determine its source. The directive exempts only three causes: a leaking blade seal, a leaking pressure relief valve, or a leaking actuator assembly. Any other cause (e.g., a leaking hub barrel, a cracked housing, a damaged gasket) triggers a requirement to remove the propeller from service. This is a broad net: the operator must physically remove the propeller and cannot dispatch the aircraft until the leak is rectified.

Maintenance records entry. The one‑time entry must state that the initial torque check was performed, that the nuts were loosened and tightened per Requirement 1.(e), and the torque values. This is a permanent record. The directive does not specify a format, but it would need to be consistent with CASR Part 42 (continuing airworthiness records).

“Before further flight” requirement. Several actions (removal of propellers found with unacceptable torque, removal of hubs with crack indications, removal of propellers with non‑exempt oil leakage) must be accomplished before the aircraft flies again. This imposes severe operational disruption but is typical for airworthiness directives addressing potential catastrophic failure (hub cracking could lead to blade separation).

The directive directly affects operators of Australian‑registered aircraft equipped with Hamilton Standard 14RF‑9, 14RF‑19 or 14RF‑21 propellers. The aircraft types explicitly listed in Note 1 are the Embraer EMB‑120, CASA CN‑235 and SAAB SF‑340, but the applicability clause is not limited to those types; any aircraft with these propeller models is caught. This includes regional airlines, charter operators, private owners, government operators, and aerial work operators (e.g., search and rescue, surveillance). If an operator holds an Air Operator’s Certificate (AOC) and operates such aircraft, the maintenance organisation contracted by that operator must also comply. The compliance burden falls on the person responsible for the continuing airworthiness of the aircraft: typically the registered operator under CASR Part 42, or the owner if the aircraft is not operated under an AOC.

Maintenance organisations that perform work on these propellers (Part 145 approved maintenance organisations or licensed aircraft maintenance engineers under Part 66) are indirectly affected because they must have access to the correct revision of the Hamilton Sundstrand MM, the facilities to perform fluorescent penetrant inspection (which requires specialised equipment and certified NDT personnel), and the lifting fixtures needed for the loosening and re‑tightening procedure. The directive also affects the manufacturer, Hamilton Sundstrand (now part of Collins Aerospace), because its maintenance manuals define the acceptance criteria and procedures. If the manufacturer revises the MM, the compliance requirements may change, but the operator must stay current with the version referenced by the directive.

The directive imposes a continuing airworthiness burden. Initially, within 30 days of the effective date (7 October 2014), all affected propellers had to undergo the baseline torque check, FPI, and one‑time loosening/re‑tightening. That initial compliance window has long passed, but the directive remains in force for any propeller that was not previously subject to the requirement (for example, a newly imported propeller, a propeller that has undergone major overhaul and was considered a “new” installation, or a propeller that was previously installed on an aircraft not operating in Australia and now enters the Australian register). The operator of that propeller must immediately comply with the initial requirements before the aircraft is operated.

Economically, the directive imposes direct compliance costs: labour for torque checks, FPI; materials (penetrant, developer, cleaning agents); potential removal and replacement costs if hubs are cracked; and opportunity costs from aircraft downtime (especially the “before further flight” requirements). For a regional airline operating multiple daily sectors, a propeller removal can ground an aircraft for several days. Operators must weigh the cost of maintaining a spare propeller pool against the risk of extended AOG (aircraft on ground) situations. The directive does not require mandatory replacement of hubs at a fixed life limit, so the costs are event-driven (when cracks are found or when torque values are out of limits). This structure incentivises operators to perform the checks carefully and to invest in quality maintenance practices to minimise the likelihood of finding cracks.

Duties. The directive imposes a series of mandatory actions, each with a specific compliance time. The operator must:

• Perform a torque check of the propeller hub retaining nuts per the applicable Hamilton Sundstrand MM. For the initial check, this must be done within 30 days of 7 October 2014 (or before first flight after that date if the propeller was not previously in service). Subsequently, it must be repeated at intervals not exceeding 500 flight hours (Requirement 2).
• Remove from service any propeller where the hub retaining nut torque does not meet the acceptance criteria. This removal must occur before further flight (Requirement 1.(b)).
• Inspect the hub dowel pin holes for cracks using the prescribed fluorescent penetrant inspection method. This inspection must be performed concurrently with any removal under Requirement 1.(b) (Requirement 1.(c)).
• Remove from service any propeller hub that shows crack indications. This must also be before further flight (Requirement 1.(d)).
• If the initial torque check is acceptable, support the propeller with an appropriate lifting fixture and loosen the hub retaining nuts, then tighten them as detailed in the MM. This must be done before further flight after completion of the initial torque check (Requirement 1.(e)).
• Make a one‑time entry in the propeller maintenance records recording that the initial torque check was performed, that the nuts were loosened and tightened, and the torque values (Requirement 1.(f)).
• When installing a propeller (including re‑installation after maintenance or replacement), use the propeller hub retaining nut tightening procedure defined in the MM and record the torque values (Requirement 3). This is a new, ongoing duty added by Amdt 4.
• Visually inspect for and investigate all external propeller oil leakage at intervals not exceeding 70 flight hours (Requirement 4.(a)).
• Remove from service any propeller where oil leakage is found to be caused by other than a leak in the blade seal, the pressure relief valve, or the actuator assembly. This removal must occur before further flight after the effective date of the directive (Requirement 4.(b)).

Rights. The directive does not explicitly grant the operator any right to deviate from the listed actions. There is no mention of an alternative method of compliance (AMOC) in the text, but under CASR Part 39, an operator can apply to CASA for an AMOC if it can demonstrate an equivalent level of safety. That is a general right under the regulatory framework, not something particular to this directive. The operator also has the right to request an extension of compliance time from CASA, but again that is a generic regulatory right and may not be routinely granted given the safety significance of hub cracking. The operator has the right to choose who performs the work (a Part 145 organisation or a licensed engineer) as long as they hold the appropriate approvals. The operator also has the right to make the one‑time maintenance records entry in any format that satisfies CASR Part 42 record‑keeping requirements.

Interaction with manuals. The directive frequently references “the applicable Hamilton Sundstrand MM”. That gives the manufacturer considerable indirect regulatory power. If the MM is revised (e.g., changes to torque values, inspection procedures, or lifting fixture requirements), the operator must follow the current revision. The directive does not freeze a specific revision of the MM, so the operator must monitor the manufacturer’s publications to ensure ongoing compliance. This is a dynamic compliance burden that can change independent of the directive itself.

The directive itself does not list penalties; that is a function of the enabling legislation. AD/PHS/18 Amdt 4 is issued under the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations (CASR), particularly Regulation 39.003 which empowers CASA to issue airworthiness directives. By operation of CASR 39.005, the operator of an aircraft to which an AD applies must ensure that the aircraft complies with the AD. Failure to do so is a breach of the Regulations and attracts the penalties set out in the Civil Aviation Act.

The Act provides for a range of enforcement measures. For a contravention of CASR Part 39, an individual can face a maximum civil penalty of 50 penalty units (currently $13,320, but indexed). A body corporate can face up to 250 penalty units ($66,600). More serious breaches may be prosecuted criminally if the conduct is reckless or intentional, with higher penalties including imprisonment for up to two years. These are maximums; actual penalties depend on the circumstances, including whether the breach contributed to an incident or fatality.

CASA has discretion to take administrative enforcement actions short of court proceedings. These include issuing a formal warning, imposing conditions on an air operator’s certificate, suspending or cancelling the certificate, or issuing an improvement notice. For operators who repeatedly fail to comply with ADs, CASA may also require increased inspection or surveillance.

In practice, CASA conducts periodic audits of operators and maintenance organisations and reviews maintenance records. If an AD compliance item is missed, CASA will typically issue a non‑compliance notice and require rectification. Deliberate non‑compliance or falsification of records is treated very seriously and may lead to prosecution. The directive’s requirement to make a one‑time entry in the propeller maintenance records (Requirement 1.(f)) creates a clear documentary trail; omission of that entry is an obvious non‑compliance that auditors can easily detect.

The directive requires recording of torque values. If those values are found to be outside the acceptance criteria and the propeller was not removed, that is a breach. If the initial torque check was acceptable but the operator failed to loosen and re‑tighten the nuts, that is also a breach. The obligations are strict: there is no defence of “it seemed fine” or “I thought it was done”.

Operators should also be aware that foreign ADs may be relevant. The directive states “FAA AD 94‑06‑05 Amdt 39‑8853 refers”. While that FAA AD is not directly enforceable in Australia, CASA may take it into account when assessing the operator’s safety culture. If a propeller maintenance action is required by both a CASA and an FAA AD, the more stringent requirement applies.

AD/PHS/18 Amdt 4 sits within the broader regulatory framework for continuing airworthiness. CASR Part 39 governs airworthiness directives generally. Part 42 (Continuing Airworthiness) imposes obligations on operators to maintain aircraft in an airworthy condition, to perform maintenance in accordance with the approved maintenance program (AMP), and to keep records. This directive effectively inserts a mandatory additional task into the AMP, overriding the operator’s normal maintenance schedule. The operator must integrate the 500‑hour torque checks and 70‑hour oil leakage inspections into their AMP, and ensure that the initial one‑time actions are accounted for even if the AMP was previously approved.

The directive interacts with CASR Part 145 (Maintenance Organisations). If an operator contracts a Part 145 AMO to perform the torque check and FPI, that AMO must hold the necessary scope of approval. FPI on propeller hubs is a specialised non‑destructive testing task; the AMO must have NDT personnel certified to Aeronautical Engineering Standard CASA AC 21‑19 or equivalent. The lifting fixture requirement also means the AMO must have access to the manufacturer‑approved tooling (or equivalent tooling approved by CASA).

The directive also interacts with Part 66 (Licensing of Aircraft Maintenance Engineers). A licensed engineer endorsing the compliance statement must hold a category B1 (mechanical) or C license appropriate for the aircraft type, and have specific training or authorisation for propeller work. For the FPI, a separate NDT certification is required; the engineer cannot simply claim to have performed the penetrant inspection without holding the relevant certification.

The directive references the Hamilton Sundstrand Maintenance Manual as the source of the torqueing procedure, the FPI method, the acceptance criteria, and the lifting fixture instructions. That means the MM, a private commercial publication, becomes de facto law. Operators must purchase or subscribe to the correct revision of that manual. If Hamilton Sundstrand issues an alert bulletin affecting the torque procedure, the operator may need to adopt that new procedure to remain in compliance with the directive, even if the directive itself is not amended. This is a dynamic interaction: the AD and the manufacturer’s manuals form a combined regulatory package.

The directive does not interact with other Australian legislation such as WHS laws directly, but the physical removal of a propeller and the FPI process involve chemicals (penetrant, developer) that require safe handling and disposal under state environmental laws. The lifting fixture requirement also invokes workplace health and safety obligations for safe lifting practices.

Importantly, the directive notes that FAA AD 94‑06‑05 refers. That FAA AD covers the same propeller models but may have different compliance requirements. In practice, CASA often harmonises with FAA ADs, but the CASA directive is the only legally enforceable standard in Australia. If a propeller is maintained under a Part 145 AMO that also holds FAA repair station certification, the AMO may need to comply with both the CASA AD and the FAA AD. Usually the stricter requirement prevails. This can create a compliance burden where the same propeller must be inspected to two slightly different standards.

The source provides the amendment history for AD/PHS/18. The original AD (unknown date) addressed insufficient torqueing procedures that caused fretting during normal propeller operation, which could lead to hub cracking. Amendment 1 (effective 27 November 2003) removed references to a manufacturer’s temporary revision and instead referred to the manufacturer’s publications that incorporated the correct torque values and procedures. This shifted the compliance basis from a temporary document to the standard maintenance manual, making it easier for operators to identify the correct procedure.

Amendment 2 (effective 9 June 2005) corrected errors in Amendment 1 without changing the intent. The source does not specify what the errors were, but typical corrections might include fixing a typographical error in a torque value or clarifying the applicability clause.

Amendment 3 (effective 22 November 2007) clarified that the loosening of the propeller hub retaining nuts and recording of torque values only has to be done initially (i.e., not on each repetitive 500‑hour check) and also when a propeller is installed to the aircraft. It also aligned the oil leakage inspection interval with FAA AD 94‑06‑05, setting it at 70 flight hours. This amendment likely reduced compliance burden by making it clear that the loosening/re‑tightening is a one‑off, not a recurring task.

Amendment 4 (effective 7 October 2014) is the current version. It clarifies the requirement for the non‑destructive inspection method - specifically that fluorescent penetrant inspection is the prescribed method - and makes minor editorial changes throughout the text. The editorial changes likely improve readability or correct cross‑references.

The amendment history shows that CASA has progressively refined the directive to reduce ambiguity and align with the manufacturer’s current procedures and the FAA AD. Operators must ensure they are using the latest amendment (Amdt 4) and not an earlier version. The background text also notes that Amendment 1, 2 and 3 compliance is considered acceptable if previously accomplished in accordance with those amendments, but the current requirements (especially the FPI clarification and the loosening/re‑tightening for installation) must still be met.

There is no mention of any litigation relating to this directive in the source text. The background does not reference any court cases, appeals, or challenges to the ADs validity. Given that the directive is a technical, prescriptive instrument issued under delegated authority, it is unlikely that any operator would challenge it in court on substantive grounds unless there was a dispute about applicability or a claim of procedural error. However, the absence of litigation does not mean none exists; it simply means the source does not record any.

It is possible that operators have sought judicial review of CASA decisions to issue or amend ADs under the Administrative Appeals Tribunal (AAT) or the Federal Court, but the directive itself does not mention any such proceedings. The very specific nature of the compliance requirements (torque checks, FPI) makes it hard to mount a successful challenge on safety merits, as CASA typically relies on manufacturer data and incident history. The most likely litigation risk would involve an enforcement action by CASA against an operator for non‑compliance, where the operator might defend on the grounds that the directive was not applicable to its aircraft or that an alternative method of compliance should have been accepted. Without specific case law, operators should proceed on the basis that the directive is fully enforceable.

That said, the directive’s reference to “Delegate of the Civil Aviation Safety Authority” (Mike Higgins) shows that the instrument was signed by a delegate, not by CASA itself. This is standard procedure, but if there were ever a challenge to the validity of the delegation, the operator would need to prove that the delegate lacked authority. That is a low bar; delegations are widely granted under the Act.

Several subtle features could catch out unwary operators or engineers.

One‑time loosening/re‑tightening is not a repetitive check. Requirement 1.(e) says “if the initial propeller hub retaining nut torque check per requirement 1.(a) is acceptable … loosen the propeller hub retaining nuts. Tighten the propeller hub retaining nuts as detailed …”. This is a one‑off task. It does not have to be repeated on every 500‑hour torque check. However, Requirement 3 says “Install all propellers using the propeller hub retaining nut tightening procedure …… Record the torque values.” That means whenever a propeller is installed (e.g., after removal for any reason, after overhaul, or when a spare propeller is fitted to an aircraft), the tightening procedure must be followed and torque values recorded. Many operators might mistakenly think that Requirement 3 is the same as Requirement 1.(e) and not bother re‑tightening on installation because they already did it once. Wrong. Requirement 3 is new and applies to every installation.

Oil leakage independence. Requirement 4.(a) requires visual inspection and investigation of all external propeller oil leakage at intervals not exceeding 70 flight hours. This is independent of the 500‑hour torque check. A propeller may pass the torque check but be unairworthy due to a small oil leak from a seal that is not the blade seal, pressure relief valve, or actuator assembly. That oil leak might not be related to the hub cracking issue at all, but the directive still requires removal. Operators must treat the 70‑hour check as a separate, recurring task. It is easy to neglect this because the oil leak check is not part of a typical scheduled inspection for many operators (they may rely on pre‑flight walkarounds). But the directive imposes a formal inspection at a fixed interval.

“Before further flight after the effective date” for oil leakage removal. Requirement 4.(b) says “Before further flight after the effective date of this Directive. … remove the propeller from service”. This means that if a propeller was already leaking from an unacceptable source before the effective date, the operator cannot dispatch the aircraft even if the leak was previously known and tolerated. The compliance clock started on 7 October 2014. For new operators taking on an aircraft after that date, the obligation applies from day one.

FPI must be performed concurrently with removal for torque. Requirement 1.(c) says “Concurrently with Requirement 1.(b).” So if a torque check fails, you must remove the propeller (1.(b)) and inspect the dowel pin holes for cracks (1.(c)) before you can consider replacing the propeller. You cannot simply re‑torque the nuts if they are loose; you must remove the hub and inspect it for cracks first. This could catch operators who assume a low torque reading is just a matter of tightening and re‑checking.

No delegation of initial torque check. The initial torque check must be done within 30 days of the effective date. That time has passed. But for a propeller that has not been previously subject to the AD (e.g., an imported aircraft), the “within 30 days” clock starts from the date the propeller first becomes subject to Australian regulation. That date could be the date of import, or the date the aircraft is registered in Australia. Operators must be careful to treat recently imported propellers as new subjects.

Maintenance records entry is one‑time, but it must include torque values. Requirement 1.(f) only requires the entry once. But Requirement 3 (on installation) also requires recording torque values. So for a propeller that is installed multiple times, torque values must be recorded each time. The initial entry cannot be used as a substitute.

The directive does not specify a “life limit” for hubs. Unlike some ADs that impose a hard life (e.g., “remove hub at 10,000 hours”), this AD is condition‑based. That means the hub could theoretically remain in service indefinitely as long as torque checks pass and no cracks appear. However, the recurring inspection and oil leakage check impose ongoing costs, and the risk of finding a crack increases with age. Operators should factor this into their fleet planning.

Compliance involves integrating the AD’s requirements into the operator’s continuing airworthiness management system. The following steps are practical guidance, assuming the operator is already familiar with CASR Part 42 and Part 145.

1. Identify affected propellers. Obtain a complete list of all aircraft in the operator’s fleet that have Hamilton Standard 14RF‑9, 14RF‑19 or 14RF‑21 propellers. This may require cross‑referencing aircraft type certificates with propeller serial numbers. Note that the AD does not exclude any serial numbers; all units of those models are covered.

2. Acquire and maintain the correct Hamilton Sundstrand MM. The AD references “the applicable Hamilton Sundstrand MM”. The operator must ensure they have the latest revision of that manual for each propeller model. The manual must include the torque procedure, acceptance criteria, FPI method, and lifting fixture instructions. If the manual is updated, the operator must update their compliance procedures accordingly. Keep a copy of the manual revision status in the propeller maintenance records.

3. Schedule initial compliance for new entrants. For any propeller that was not previously subject to AD/PHS/18 (e.g., newly imported, newly manufactured, or previously installed on a non‑Australian aircraft), the operator must:

• Within 30 days of the propeller entering service in Australia (or before flight, whichever comes sooner), perform the initial torque check (Requirement 1.(a)).
• If the torque check passes: loosen and re‑tighten the hub retaining nuts per Requirement 1.(e), then make the one‑time maintenance record entry per Requirement 1.(f).
• If the torque check fails: remove the propeller from service. Concurrently, perform the fluorescent penetrant inspection of the dowel pin holes. If cracks are found, remove the hub. If no cracks, the hub may be reused after the torque issue is rectified (likely by re‑torquing and possibly replacing nuts or washers).
• Record all actions in the propeller maintenance records.

4. Establish repetitive checks.

• 500‑hour torque check: Add this task to the approved maintenance program (AMP). The check should be performed every 500 flight hours from the last initial or repeat check. Ensure the engineer has access to the correct torque values and that the propeller is not loosened unless a failed check requires removal. Note: loosening and re‑tightening is not required at each 500‑hour check; only the torque is verified.
• 70‑hour oil leakage inspection: Add this task to the AMP as well. This is a simple visual inspection, but it must be formally scheduled. The engineer must investigate any leakage and determine the source. If the source is not one of the three exempted items, the propeller must be removed before further flight.

5. Manage propeller installations. When a propeller is installed (whether new, overhauled, or a spare), follow Requirement 3: use the tightening procedure from the MM and record the torque values. This may also trigger the one‑time loosening/re‑tightening if the propeller has never had it done (for example, a propeller that was previously operated without having had the initial action). Keep a log of installation dates and torque values.

6. Maintain records. The propeller maintenance records must contain:

• Evidence of the one‑time initial loosening/re‑tightening (if applicable), including torque values.
• For each 500‑hour torque check, a record of the torque values and an assessment of acceptability.
• For each 70‑hour oil leakage inspection, a record of the inspection and any findings.
• If a propeller is removed for non‑compliance, a record of the removal reason and the outcome of the FPI (if applicable).

These records should be kept for the life of the propeller and transferred with the propeller if it is sold or moved to another aircraft.

7. Train staff. Engineers performing the torque check must be familiar with the Hamilton Sundstrand MM and the specific lifting fixture. FPI must be performed by an NDT technician certified to the appropriate standard. Engineers performing the oil leakage inspection must know how to distinguish acceptable leaks (blade seal, pressure relief valve, actuator) from unacceptable leaks.

8. Monitor for manual revisions. The AD does not freeze the manual revision, so any change to the MM could affect torque values, inspection procedures, or acceptance criteria. The operator should subscribe to Hamilton Sundstrand service bulletins or subscribe to a revision‑tracking service. If the manual changes the tightening procedure, the operator must adopt it immediately to remain compliant.

9. Consider using a Part 145 AMO. Operators without in‑house capability should contract a Part 145‑approved maintenance organisation that holds the necessary scope for propeller work, including NDT. Ensure the contract clearly assigns responsibility for complying with this AD.

10. Document internal procedures. Create a written procedure that cross‑references the AD requirements to specific maintenance tasks in the AMP. This will assist during CASA audits and help avoid missed inspections or erroneous assumptions about one‑time versus repetitive tasks.