AD/APU/18 - Fuel Leaks on Hamilton Sundstrand APU Models T-62T-46C12 and T-62T-40C14

The instrument organizes a small set of technical and operational obligations around a single identified unsafe condition and a limited set of parts. Key concepts in the text are: (1) applicability by APU model and by installed fuel filter housing part numbers (Applicability); (2) prescriptive corrective action in the form of bracket installation and an associated inspection/adjustment procedure for certain previously installed brackets (Requirement); (3) a specific compliance interval measured in hours time‑in‑service or calendar time, whichever occurs earlier (Compliance); (4) linkage to manufacturer service literature (two ASBs by Hamilton Sundstrand) as the technical method of compliance (Requirement); and (5) a note that substituting an alternative fuel filter assembly part number (not listed in the AD) for the APS 500R model functions as an optional terminating action (Requirement, Note 2). The AD’s background statement identifies a failure mode , cracked or failed fuel bypass button protruding beyond the internal o‑ring seal , and ties the corrective measure directly to eliminating fuel leakage that could cause fire or explosion (Background).

Operationally the AD creates a mandatory conformity requirement: affected APUs that meet the applicability criteria are required to be modified or inspected and adjusted according to the cited ASB procedures within the stated compliance window. The AD instructs maintenance actions to be carried out "as per provisions of" the specific ASBs; where earlier ASB versions were used for prior installations, the AD requires a one‑time inspection and, if necessary, adjustment according to specific paragraphs of the later ASB revision (Requirement). The AD also recognises an alternative path to termination of the AD for the T‑62T‑40C14 APS 500R model , installing a fuel filter assembly outside the P/Ns listed , which creates a technical substitution route rather than requiring bracket retrofit if the operator changes to a different P/N part (Requirement, Note 2). The AD cross‑references FAA AD 2004‑24‑03 (Note 3), establishing a link to an external airworthiness action.

The AD affects owners, operators and maintainers of aircraft that have Hamilton Sundstrand Power Systems APU Models T‑62T‑46C12 and T‑62T‑40C14 (APS 500R) where the fuel filter housing assemblies with part numbers 4951627, 4951960, or 4952039 are installed (Applicability). The text explicitly notes that these APUs are installed on, but not limited to, Bombardier DHC‑8‑400 airplanes and Empresa Brasileira de Aeronautica S.A. (EMBRAER) EMB‑135 and EMB‑145 series aircraft; the phrase "but not limited to" signals that other aircraft types with the affected APUs are also captured by the applicability statement (Applicability). The responsible parties for performing the mandated actions will therefore be the aircraft operators or their approved maintenance organisations that maintain and certify the airworthiness of those APUs, since the AD requires installation and inspection tasks specified in manufacturer ASBs (Requirement).

Because the AD operates at the level of the APU and its installed parts, organisations that manage maintenance records, parts identification and compliance tracking for affected fleets must be involved. Specifically, those who need to determine applicability must check the installed fuel filter housing assembly part numbers (4951627, 4951960, 4952039) on each APU to decide whether the AD applies to that unit (Applicability). Where a bracket has already been installed, the previous installation method matters: if the bracket was fitted using the original issue of ASB‑4504112‑49‑22 dated 2 December 2003, the operator must perform the one‑time inspection and gap adjustment process specified in ASB‑4504112‑49‑22 Revision 2 dated 4 October 2004 (Requirement). The AD also affects procurement/parts management decisions: for the T‑62T‑40C14 APS 500R, operators have the option to fit a fuel filter assembly with a part number not listed in the AD as an alternative terminating action; that requires parts acquisition and parts‑compatibility assessment (Requirement, Note 2).

While the AD does not name maintenance personnel categories or licence levels, the reliance on ASB procedural instructions implies that the work is to be carried out by personnel capable of accomplishing the manufacturer's Accomplishment Instructions and recording compliance in maintenance logs. The AD does not itself specify record‑keeping detail beyond the compliance timing, so affected organisations must translate the AD requirements into their internal maintenance control and quality assurance processes. The instrument also references FAA AD 2004‑24‑03, so operators with international fleets or dual‑jurisdiction operations should note that related FAA direction exists (Note 3).

Duties imposed by the AD are prescriptive and technical. The primary duties are:

• Determine applicability by confirming APU model and that the fuel filter housing assembly installed is one of the specified part numbers: 4951627, 4951960, or 4952039 (Applicability). This is the prerequisite screening duty for the rest of the AD.

• For APU Model T‑62T‑46C12, install a bracket onto the fuel filter housing assembly in accordance with Hamilton Sundstrand ASB No. ASB‑4503067‑49‑9 dated 2 December 2003 (Requirement).

• For APU Model T‑62T‑40C14 (APS 500R), unless a bracket has been previously installed, install a bracket per Hamilton Sundstrand ASB‑4504112‑49‑22 Revision 2 dated 4 October 2004 (Requirement).

• For brackets that were previously installed using the Original Issue of ASB‑4504112‑49‑22 dated 2 December 2003, perform a one‑time inspection for proper gap and, if necessary, adjust the gap between the bracket and the bypass button using paragraph 2.B. and 2.D.(1) of the Accomplishment Instructions of ASB‑4504112‑49‑22 Revision 2 (Requirement).

• Comply within the stated interval: within 500 hours time‑in‑service or six months after the effective date of the AD, whichever occurs earlier (Compliance).

Rights or options preserved by the AD are limited but explicit. The AD provides an optional terminating action for the T‑62T‑40C14 (APS 500R) model: installing a fuel filter assembly with a part number not listed in the AD is described as an optional terminating action to the AD’s requirements for that model (Requirement, Note 2). That creates a technical choice for operators: either perform the bracket installation/inspection/adjustment route or change the installed fuel filter assembly part number to an alternative not listed in the AD.

The AD ties the required actions to manufacturer ASBs, which defines the method of compliance. This creates a duty to follow the ASB provisions specified: work must be "as per provisions of" the named ASBs (Requirement). For previously installed brackets built to the original ASB, the AD adds a specific inspection/adjustment duty that points to precise paragraphs of the revised ASB (Requirement). The AD does not otherwise specify the detailed technical steps, instead delegating the method to the ASB instructions.

The AD imposes a clear compliance window and effective date: it became effective on 17 March 2005 and requires action within the earlier of 500 hours TIS or six months from that date (Compliance; effective date). The AD does not, within the supplied text, specify who is to certify completion or the exact form of the proof of compliance, nor does it set out any revision procedure or exemptions; the only alternative explicitly allowed is the optional terminating action for the APS 500R model (Requirement, Note 2).

The AD text provided sets out mandatory actions and an effective date, but it contains no express penalty schedule or enforcement mechanism within the supplied material. The AD states that it "becomes effective on 17 March 2005" and is issued by a delegate of the Civil Aviation Safety Authority (signature block). Beyond that, the text does not list fines, suspension powers, administrative penalties, or criminal sanctions, nor does it describe inspection, audit or remedial enforcement steps (effective date and signature). Therefore, within the bounds of the text provided, there is no explicit statement of enforcement procedures or penalties.

Practically, the AD prescribes technical compliance within a stated timeframe , the earlier of 500 hours time‑in‑service or six months after the AD’s effective date , and requires installation actions and a specified one‑time inspection for certain previously installed brackets (Compliance; Requirement). Because the AD references specific manufacturer ASBs as the work‑scope documents, compliance will be demonstrable by maintenance records that show the ASB tasks were accomplished within the prescribed interval. The AD itself does not define the form or contents of such records.

The AD also cross‑references FAA Airworthiness Directive 2004‑24‑03 (Note 3), but the supplied text does not explain whether or how that FAA AD interacts with Australian enforcement regimes. The absence of enforcement detail in the text means that any statements about administrative or criminal enforcement, sanctioning processes, or the role of other regulatory instruments are not supported by the document itself. Readers who require the enforcement regime and penalties applicable to failure to comply should consult the broader regulatory framework outside this AD; those materials are not part of the supplied text and therefore are not described here.

Within the confines of the supplied material, the AD expressly interacts with two types of external instruments: manufacturer service bulletins (ASBs) and an FAA airworthiness directive. The AD requires specific actions "as per provisions" of Hamilton Sundstrand Alert Service Bulletin No. ASB‑4503067‑49‑9 dated 2 December 2003 for the T‑62T‑46C12, and ASB‑4504112‑49‑22 Revision 2 dated 4 October 2004 for the T‑62T‑40C14 APS 500R (Requirement). For previously installed brackets using the original issue of ASB‑4504112‑49‑22 dated 2 December 2003, the AD mandates a one‑time inspection and potential adjustment using paragraph 2.B. and 2.D.(1) of the Accomplishment Instructions of ASB‑4504112‑49‑22 Revision 2 (Requirement). That structure makes the manufacturer ASBs the required method of compliance: the AD delegates the technical procedure for compliance to those documents and incorporates them by reference for the specified tasks.

The AD additionally refers to FAA Airworthiness Directive 2004‑24‑03 Amendment 39‑13879 (Requirement, Note 3). The supplied text does not detail the FAA AD’s contents, the scope of its directives, nor any reciprocity or coordination mechanism between CASA and the FAA. All that can be stated from the AD is that the FAA AD is acknowledged as related and that the CASA AD notes that the FAA AD "refers" (Note 3).

The AD provides an alternative terminating action for the APS 500R model by permitting the installation of a fuel filter assembly with a part number not listed in this AD, which is described as an optional terminating action (Requirement, Note 2). This creates a technical interface between parts management and airworthiness compliance: changing the installed part number to one outside the AD’s list is accepted by this AD as a way to terminate the obligation. The AD does not specify approval or acceptance criteria for such alternative parts beyond stating the effect in the AD text.

Conversely, the AD does not reference other Australian statutory provisions, civil aviation regulations, or processes for waivers and exemptions within the supplied document. It does not explicitly state how compliance with the AD must be recorded or certified under other obligations. Therefore, while the AD incorporates manufacturer ASBs and acknowledges an FAA AD, any interaction with other laws or regulatory instruments beyond those referenced is not described in the text provided.

The supplied text contains the issuance details of this AD and references to particular revisions of manufacturer service bulletins, but it does not show any subsequent amendments to the AD itself. The AD is labelled AD/APU/18 (3/2005) and is dated 4 February 2005 in the signature block; it states that the Airworthiness Directive becomes effective on 17 March 2005 (signature block; effective date). Within the Requirement text, the AD distinguishes between different versions of the Hamilton Sundstrand ASBs: it instructs compliance with ASB‑4503067‑49‑9 dated 2 December 2003 for the T‑62T‑46C12, and ASB‑4504112‑49‑22 Revision 2 dated 4 October 2004 for the T‑62T‑40C14 APS 500R; it also references the original issue of ASB‑4504112‑49‑22 dated 2 December 2003 for the purpose of requiring a one‑time inspection where brackets were installed under that original issue (Requirement). These references indicate the AD was issued after those ASBs and that the AD incorporates specific ASB revision dates as the authorised compliance documents.

The AD text does not itself present a revision log for the AD, nor does it include later amendment statements, supersessions, revocations, or effective‑date changes within the supplied material. Nor does it include a chronological history beyond the single issuance date and the embedded ASB revision references. The only amendment‑type material visible in the AD relates to the ASB revision sequence (original issue dated 2 December 2003 and Revision 2 dated 4 October 2004) and the AD’s employment of Revision 2 for compliance and for the inspection procedure to correct earlier installations that followed the original ASB (Requirement). If users need to know whether the AD was later amended, superseded or revoked, that information is not present in the provided text and would need to be obtained from the issuing authority’s update records.

The supplied AD contains no information about litigation, disputes, court decisions, administrative appeals, or precedential enforcement actions related to this directive. The text does not mention any legal challenges, interpretations, or case names. It purely sets out applicability, the required technical actions (referencing manufacturer ASBs), the compliance timeframe, an effective date, and the background safety rationale for the measure (Background; Requirement; Compliance; effective date).

Therefore, within the limits of the document provided, there is no litigation history to report. Any litigation or administrative proceedings that may have arisen in relation to this AD would not be reflected in the supplied material and would need to be researched in appropriate case law databases, tribunal records, or regulator enforcement archives external to this AD text.

The AD contains several technical and procedural details that can be sources of error or misunderstanding unless carefully observed:

• Applicability is by both APU model and specific fuel filter housing part numbers. The AD applies to Hamilton Sundstrand Power Systems Models T‑62T‑46C12 and T‑62T‑40C14 (APS 500R) APUs with fuel filter housing assemblies P/Ns 4951627, 4951960, or 4952039 installed (Applicability). Operators must check installed part numbers rather than relying solely on aircraft type or APU model alone. The AD explicitly notes examples of aircraft types on which these APUs appear (Bombardier DHC‑8‑400 and EMB‑135/145) but adds "but not limited to", so applicability is not confined to those airframes (Applicability). A routine mistake would be to assume the AD only applies to those airframes; instead the determining factor is the APU and the installed P/N.

• The AD distinguishes between brackets previously installed and brackets not installed. For the T‑62T‑40C14 APS 500R model, the text says "Unless previously installed, install a bracket ... as per ... ASB‑4504112‑49‑22 Revision 2 dated 4 October 2004" (Requirement). Where a bracket was previously installed using the original issue of that ASB (dated 2 December 2003), a one‑time inspection and possible adjustment is explicitly required, using specified paragraphs of the ASB Revision 2 (Requirement). A potential gotcha is failing to confirm which ASB issue was used for any existing bracket installation; if the original ASB was used, inspection and adjustment are mandatory even though a bracket is already present.

• The AD provides an alternative terminating action for the APS 500R model by installing a fuel filter assembly with a part number not listed in the AD (Requirement, Note 2). Operators might assume that replacing the bracket or changing other components achieves termination, but the AD specifically identifies replacement of the fuel filter assembly part number as an optional terminating action; nothing else is described as terminating.

• Compliance timing is the earlier of 500 hours time‑in‑service or six months after the AD’s effective date (Compliance). A common operational slip would be to miscalculate effective date deadlines, especially when interacting with aircraft scheduled maintenance cycles. The AD’s effective date is given as 17 March 2005, and the compliance window is tied to that effective date; failure to convert calendar time to the maintenance cycles used by the operator could lead to missed compliance.

• The AD incorporates manufacturer ASBs as the method of compliance and cites particular paragraphs for the one‑time inspection and adjustment (Requirement). A gotcha is performing the physical work without strict adherence to the specified ASB provisions or without recording that the specific ASB paragraphs were followed. The AD does not reproduce the ASB text; it requires compliance "as per provisions of" the identified ASBs.

• The AD refers to FAA AD 2004‑24‑03 (Note 3). Operators who work across jurisdictions must not assume that different wording or compliance paths in the FAA AD will automatically satisfy this CASA AD unless the work was carried out exactly as required by this AD and the specified ASBs.

• The AD does not set out enforcement or penalty provisions in the provided text. That lack of explicit enforcement language is not a licence to defer action; rather, it requires operators to understand how their maintenance control and regulatory compliance systems will record and evidence completion because the AD sets mandatory actions with a definitive compliance window (Compliance).

Careful documentation of installed part numbers, record of which ASB issue was used for any prior bracket installations, and confirmation that any alternative fuel filter assembly P/N is not one of the listed P/Ns are practical steps to avoid non‑compliance traps inherent in the AD wording.

Follow these steps, derived directly from the AD text, to bring an affected APU into compliance:

1. Applicability check. Inspect the APU to determine whether it is one of the Hamilton Sundstrand Power Systems models T‑62T‑46C12 or T‑62T‑40C14 (APS 500R) and whether the fuel filter housing assembly installed is part number 4951627, 4951960, or 4952039 (Applicability). Record the part number and APU serial/identification in maintenance records.

2. Decide the compliance path. For each applicable APU, determine whether a bracket is already installed on the fuel filter housing assembly. If no bracket is present, the bracket installation is required. If a bracket is present, determine which ASB (and which issue/revision) was used for the previous installation (Requirement).

3. For T‑62T‑46C12 units without a bracket, effect bracket installation using Hamilton Sundstrand Alert Service Bulletin ASB‑4503067‑49‑9 dated 2 December 2003. The AD requires bracket installation "as per provisions" of that ASB (Requirement). Ensure the ASB work package is available and follow its Accomplishment Instructions. Record completion in the aircraft/APU maintenance log.

4. For T‑62T‑40C14 (APS 500R) units without a bracket, install the bracket per Hamilton Sundstrand ASB‑4504112‑49‑22 Revision 2 dated 4 October 2004 (Requirement). Again, follow the ASB’s Accomplishment Instructions in full and retain the applicable pages and sign‑offs in maintenance records.

5. For T‑62T‑40C14 (APS 500R) units where a bracket was previously installed using the Original Issue of ASB‑4504112‑49‑22 dated 2 December 2003, perform the one‑time inspection for proper gap and, if required, adjust the gap between the bracket and the bypass button using paragraph 2.B. and 2.D.(1) of the Accomplishment Instructions of ASB‑4504112‑49‑22 Revision 2 dated 4 October 2004 (Requirement). Ensure the specified paragraphs are cited in the maintenance record to evidence that the AD‑required inspection and adjustment were performed.

6. Optional terminating action (for APS 500R). Consider whether replacing the installed fuel filter assembly with a part number not listed in this AD is feasible for the affected unit. The AD states that installation of a fuel filter assembly with a part number not listed in this AD "constitutes optional terminating action to the requirements of this AD" for the T‑62T‑40C14 (APS 500R) model (Requirement, Note 2). If that route is chosen, procure the alternate filter assembly part, install it in accordance with approved procedures, and document the part number change and the rationale that this is the optional terminating action named in the AD.

7. Meet the compliance timing. All required installations and the one‑time inspections/adjustments must be completed within the earlier of 500 hours time‑in‑service or six months after the effective date of the AD (Compliance). The AD’s effective date is stated as 17 March 2005; compute scheduled compliance against that date and the APU’s usage hours to ensure completion within the stipulated window. Where planning or scheduling could otherwise defer the work beyond the AD’s window, operators must prioritise the mandated actions to meet the time or TIS threshold.

8. Record keeping. The AD does not spell out the exact format for compliance records, but the work is mandated "as per provisions of" the specified ASBs and the AD references specific ASB paragraphs for inspections. Therefore, maintenance logs should explicitly note the AD identifier (AD/APU/18 (3/2005)), the ASB used (including revision/date), the performed actions (installation, inspection, adjustments), the relevant paragraph citations where required, the parts installed (including part numbers), the hours time‑in‑service at which the actions were performed, and the signature of the person certifying the work. Retain the ASB work cards and any associated parts‑change documentation that evidence compliance.

9. Cross‑reference FAA AD. The AD notes that FAA Airworthiness Directive 2004‑24‑03 Amendment 39‑13879 refers (Requirement, Note 3). Where operators maintain records for international regulatory compliance, include references to the FAA AD as relevant, and ensure the CASA AD’s specific requirements have been met in addition to any FAA direction.

10. Quality and oversight. Ensure the tasks are performed by appropriately qualified maintenance personnel and that the work follows the ASB Accomplishment Instructions exactly, particularly for the one‑time gap inspection and any adjustment. Because the AD requires compliance with specific ASB procedures and citations, deviation from those procedures risks non‑compliance.

Following these steps will implement the bracket installation and inspection/adjustment obligations stated in the AD within the compliance window. The AD provides no other compliance alternatives beyond the optional terminating action specified for the APS 500R model; do not assume other measures satisfy the AD unless they match the AD text.