AD/HS 125/177 - Hydraulic Over-Temperature Switch Fuse

The Directive rests on a small set of concrete technical and regulatory concepts drawn directly from the text.

• Applicability and scope: only the narrow numeric range of Raytheon Model Hawker 800XP serial numbers listed are within scope. The AD’s Applicability clause sets the universe of aircraft that must comply: "serial numbers 258541, 258556, and 258567 through 258713 inclusive." The list is specific and excludes other Hawker 800XP airframes.

• Inspection requirement: a "general visual inspection" is required to determine whether a 20-amp fuse is installed in the hydraulic over-temperature switch electrical circuit on panel ZK in the rear equipment bay. The AD points the operator directly to the Accomplishment Instructions of Raytheon Service Bulletin SB 24-3724 (May 2005) as the step-by-step reference for carrying out that inspection. The phrase "If not previously accomplished, carry out a general visual inspection" indicates the AD recognises prior compliance if it exists.

• Corrective action: if the inspection shows a 20-amp fuse is present, the AD requires replacement with a 3-amp fuse. The replacement must be performed "in accordance with the Accomplishment Instructions of the SB 24-3724." The AD also provides for repair of any damage detected: "If signs of damage are found contact the Raytheon Aircraft Company for applicable repair actions and carry out the specified repairs."

• Timing and flight safety gating: the AD sets a two-step timing regime. The inspection must occur "Within 50 flight hours or 30 days after the effective date ... whichever occurs first." Any required replacement or repair must be done "Before further flight." That gating converts a maintenance action into a potential grounding action if a defect is found and not corrected, because continued flight is prohibited until the corrective action is complete.

• Reference to manufacturer procedure and foreign regulator action: the AD explicitly invokes Raytheon Service Bulletin SB 24-3724 (May 2005) as the normative technical instruction and references FAA AD 2006-02-03 Amdt 39-14455 in a Note. The Background attributes the directive to advice from the FAA based on "a report of the installation of an incorrect fuse ... during aeroplane maintenance."

• Objective and hazard: the Background states the objective is to "prevent possible heat damage to associated wiring and surrounding equipment, which could result in smoke or fire on the aeroplane, when the incorrectly rated fuse fails to blow." This provides the risk mechanism the AD seeks to interrupt: misinstalled higher-rated fuse → no fuse blow during over-temperature → heat damage → smoke/fire risk.

These concepts are all present in the Directive text and together create a compliance regime that ties a specific maintenance check and corrective action to continued airworthiness within a narrowly defined fleet subset.

The Directive identifies several discrete actors and constituencies who will be affected directly or indirectly.

• Aircraft owners and operators of the specified Hawker 800XP serial numbers are the primary parties who must comply. The Applicability language , "Raytheon Model Hawker 800XP aeroplanes, serial numbers 258541, 258556, and 258567 through 258713 inclusive" , draws a precise obligation to that set of operators. Those operators must ensure the inspection and any consequent replacement or repair occur within the specified timeframes.

• Maintenance organisations and certificated maintenance personnel who perform the inspection and replacement carry the duty to follow the "Accomplishment Instructions of Raytheon Service Bulletin SB 24-3724, dated May 2005." The AD places the procedural authority for how to do the work into the manufacturer’s service bulletin rather than spelling out the exact steps in the AD text.

• The Raytheon Aircraft Company is named as the contact for repair actions if damage is discovered: "If signs of damage are found contact the Raytheon Aircraft Company for applicable repair actions and carry out the specified repairs." This assigns Raytheon a direct role in prescribing repairs and, implicitly, in providing technical support or approved repair methodologies.

• The Civil Aviation Safety Authority (CASA) is the issuing regulator; the document is signed by "James Coyne, Delegate of the Civil Aviation Safety Authority." That shows who decides to issue and enforce the AD within the Australian regulatory framework.

• Regulators and maintainers outside Australia are indirectly implicated by the Note referencing the United States FAA AD 2006-02-03. The AD explicitly follows advice from the FAA, so overseas operators and their maintenance providers who operate common airframes may need to consider harmonised requirements.

• Passengers and crew are affected only indirectly through the improved mitigation of the "smoke or fire" risk stated in Background. The AD does not impose obligations on them directly.

• Third-party parts suppliers and logistics providers are implicated practically because replacement of an incorrect 20-amp fuse with a 3-amp fuse requires the availability of the correct part and possibly lead time to source it.

Costs, time and operational impacts fall primarily on the operators and their maintenance suppliers: they must schedule and perform the inspection within 50 flight hours or 30 days, and must not permit further flight if corrective action is required until the replacement/repair is completed. The AD’s limited serial-number scope narrows the total population affected, concentrating compliance obligations on operators of those specific aeroplanes.

The AD prescribes specific duties and sets out certain procedural rights implicitly by reference to manufacturer and regulator instruments.

Duties

• Inspect within the mandated window. The AD requires that "If not previously accomplished, carry out a general visual inspection ... in accordance with the Accomplishment Instructions of Raytheon Service Bulletin SB 24-3724, dated May 2005." The compliance period is explicit: "Within 50 flight hours or 30 days after the effective date of this Directive, whichever occurs first."

• Replace an incorrect fuse. Where the inspection "determines if a 20-amp fuse is installed ... replace it with a 3-amp fuse in accordance with the Accomplishment Instructions of the SB 24-3724." The AD requires this replacement "Before further flight after the Requirement 1 inspection."

• Repair damage. The AD imposes a duty to contact Raytheon and carry out "applicable repair actions" if "signs of damage are found." The AD does not specify repair detail; it delegates the repair method to Raytheon.

• Follow manufacturer instructions. The AD repeatedly ties both inspection and replacement/repair to the Accomplishment Instructions of SB 24-3724, which effectively mandates adherence to that Service Bulletin as the procedural standard.

Rights and procedural implications

• Prior compliance acknowledgment. The text states "If not previously accomplished," which recognises the right of an operator to rely on earlier work if the SB actions have already been carried out. That phrasing allows an operator who has evidence of prior compliant work to avoid repeating the required inspection.

• Manufacturer direction for repairs. If damage is present, operators must contact Raytheon for "applicable repair actions." This gives Raytheon the authoritative role to specify acceptable repairs; operators have the right to receive repair instructions from the manufacturer but do not have an expressed right in the AD to use alternative repair data.

• Flight restriction until remedied. By requiring replacement and repairs "Before further flight after the Requirement 1 inspection," the AD effectively prohibits continuing operations with an unresolved 20-amp fuse or unrepaired damage. While the AD does not set out a formal suspension mechanism in the text, the "before further flight" requirement is a direct operational constraint that must be observed.

• No explicit liberty to defer. The AD specifies the inspection timeframe and the "before further flight" rule, with no language allowing deferred compliance beyond the stated windows. There is no provision in the text for an alternative method of compliance, an exemption, or a permanent modification procedure; all corrective action is tied to the Raytheon service bulletin and manufacturer repair direction.

• Delegated issuance and enforcement. The document is issued by a named delegate of CASA. That signals the regulatory source of the duty and establishes the body responsible for oversight.

In sum, the AD places specific, time-limited duties on operators and maintainers, requires conformity to manufacturer instructions for inspection and repair, and constrains continued flight pending correction where a non-conforming fuse or damage is found. The AD allows prior compliant work to be recognised but sets no explicit alternative compliance or exemption process within the text.

The Directive text itself sets operationally binding compliance requirements and timelines, but it contains no explicit penalty schedule or enforcement mechanism within the text provided. The AD states action items and timing: the inspection must occur "Within 50 flight hours or 30 days after the effective date of this Directive, whichever occurs first," and any necessary replacement or repairs must be performed "Before further flight after the Requirement 1 inspection." The AD also states its effective date: "This Airworthiness Directive becomes effective on 24 February 2006."

What the text does not contain, based solely on the supplied instrument, is any express provision describing civil, administrative or criminal sanctions applicable for non-compliance, nor any process for compliance monitoring, reporting of completion, or approving alternative methods of compliance. The AD does not set out a compliance reporting form, record-keeping specification, or a certification attestation process. It likewise does not specify enforcement procedures such as notice periods, fines, grounding orders, or timelines for regulator inspection.

However, the document is issued by the Civil Aviation Safety Authority (CASA), as indicated by the signature block "James Coyne, Delegate of the Civil Aviation Safety Authority." That indicates the AD is a regulatory instrument within CASA’s airworthiness framework; in practice, Australian airworthiness directives by CASA are enforceable regulatory measures. The AD’s operational requirements (inspection within a short window and mandatory replacement before further flight) create an immediate compliance obligation that, if not observed, would leave the aircraft operating in breach of the Directive and potentially of applicable airworthiness certification rules.

Given the text supplied, consequences for non-compliance are left implicit rather than enumerated: failure to comply with the inspection and corrective action would result in the operator flying an aeroplane that the AD has identified as having a potentially unsafe configuration, namely the presence of an incorrectly rated fuse that could prevent protective operation and result in heat damage. The AD frames the safety hazard but does not attach visible penalties within its language. Enforcement and penalties, if any, would therefore arise from CASA’s broader regulatory powers, which are not described in this document.

Lastly, the Note referencing "FAA AD 2006-02-03 Amdt 39-14455" signals co-ordination with the FAA; the FAA AD regime normally contains its own enforcement mechanisms for US-registered aircraft, but the AD text does not detail reciprocal enforcement arrangements.

The text of this Directive is narrowly technical and refers expressly to a foreign regulator’s action and to manufacturer service instructions. Within the supplied text, two explicit interactions are present.

• Connection with FAA action. The AD includes a Note: "FAA AD 2006-02-03 Amdt 39-14455 refers." The Background states that the Directive "follows advice from the United States Federal Aviation Administration (FAA) regarding a report of the installation of an incorrect fuse." This shows the Directive is aligned with or reactive to an FAA airworthiness action. The interaction is one of informational and substantive alignment: CASA adopted an action addressing the same defect reported and acted on by the FAA. Operators who are subject to both jurisdictions, or whose parts and maintenance follow US standards, must take account of both instruments.

• Reliance on manufacturer service bulletin as the normative technical source. The AD requires actions to be carried out "in accordance with the Accomplishment Instructions of Raytheon Service Bulletin SB 24-3724, dated May 2005." That makes the Service Bulletin the delegated technical specification for safe compliance. The AD therefore interacts with private technical standards produced by the aircraft manufacturer, incorporating them by reference as the required method of compliance.

The AD does not, in the supplied text, mention other Australian statutory provisions, civil aviation regulations, certification rules, or administrative procedures. It does not reference CASA enforcement instruments, Parts of the Civil Aviation Regulations, or specific record-keeping obligations. Consequently, while the AD sits in a legal and regulatory ecosystem where non-compliance would likely engage other laws and enforcement mechanisms, the Directive text itself does not set out those cross-references.

There is a procedural interaction implicit in the "If not previously accomplished" phrasing. Operators who already complied with the SB or equivalent action prior to the AD's effective date are implicitly allowed to rely on that earlier action and need not repeat it. That creates an interaction between past maintenance records and the AD’s requirement; operators will need to demonstrate prior compliance to avoid duplication.

Other potential interactions that the AD does not address explicitly in the supplied text include:

• how compliance is to be recorded in aircraft maintenance logs;
• whether alternative repair methods must be pre-approved by CASA or Raytheon; and
• whether an operator may petition CASA for an Alternative Method of Compliance (AMOC).

In short, the Directive interacts explicitly with the FAA’s corresponding AD for the same unsafe condition and with the Raytheon Service Bulletin for the technical method of compliance; it does not set out other statutory cross-references or procedural interactions in the text provided.

The supplied document contains no explicit amendment history entries beyond its issuance and effective dates. The AD is identified as "AD/HS 125/177 Hydraulic Over-Temperature Switch Fuse 4/2006 DM" and the textual details state that "This Airworthiness Directive becomes effective on 24 February 2006." The document is dated "6 February 2006" where it is signed by the CASA delegate, James Coyne. No later amendments, revocations, supersessions, or update notices appear in the provided text.

The AD does, however, reference an external FAA action (FAA AD 2006-02-03 Amdt 39-14455), which may indicate contemporaneous coordination and could be the basis for future amendment if further information arose. The AD also ties its procedural requirements to Raytheon Service Bulletin SB 24-3724 dated May 2005. Any subsequent revision of that Service Bulletin could in practice give rise to an amendment or clarification of the AD, but the AD itself does not record any linkage to updated SB revisions.

Because there is no amendment log in the supplied text:

• there is no recorded history of prior amendments to this AD in the document;
• there is no list of superseded ADs or cross-references to earlier CASA instruments; and
• there is no statement of an expiry date, nor a follow-up AD.

Users and compliance officers should therefore treat the AD as a single-issue instrument that became effective on 24 February 2006 and, absent external sources not included here, has no in-text amendment history. Any subsequent amendments, if they exist, are outside the scope of the provided text and are not described in this document.

The supplied Directive contains no litigation history or references to judicial or administrative proceedings. There are no mentions of appeals, challenges, reviews, or determinations arising from the AD in the text. The document is a technical regulatory instrument and is limited to stating the safety concern, the affected aircraft serial numbers, the required inspections and corrective actions, and the compliance timings.

Because the AD does not include any litigation history, there are no judicial decisions, case names, or dispute outcomes referenced in the text that could be used to interpret or test the Directive’s legal effect. Any administrative enforcement actions, compliance disputes, or litigation that may have arisen in practice are not recorded in this instrument.

If an operator or maintenance organisation sought to contest the AD’s requirements, that process and its outcomes would be governed by broader administrative law and aviation regulation procedures, which are not set out in the Directive itself. The absence of litigation information in the AD means that users must rely on external sources (not contained in this document) to determine whether the AD was litigated, the extent of any enforcement actions taken by CASA, or whether the AD was amended following any contested proceedings.

The AD’s brevity and narrow scope create several practical points that can lead to misunderstanding or operational risk if not attended to carefully.

• Narrow serial-number scope. The Applicability clause lists specific serial numbers only. Operators might assume other Hawker 800XP models are covered; the AD is explicit and limited: "serial numbers 258541, 258556, and 258567 through 258713 inclusive." Operators of aircraft just outside that range may be tempted to infer risk parity, but the Directive applies only to the listed serial numbers as written. That tight scope concentrates the obligations and the operational impact.

• The inspection is a "general visual inspection" but must follow SB instructions. The AD says to "carry out a general visual inspection ... in accordance with the Accomplishment Instructions of Raytheon Service Bulletin SB 24-3724, dated May 2005." There is a potential mismatch between the term "general visual inspection" and the more prescriptive steps that may be found in the Service Bulletin. Compliance requires consulting and following the SB; simply doing a cursory visual check might not satisfy the AD if the SB prescribes particular panels, lighting, or removal of coverings to gain proper access.

• Discrepancy between fuse marking and installation. The AD targets the presence of a 20-amp fuse where a 3-amp fuse is required. Maintenance personnel should not rely solely on visual inspection of an installed fuse’s markings without following SB instructions, because the AD’s corrective step is replacement with a 3-amp fuse "in accordance with the Accomplishment Instructions." The AD does not specify whether an appropriately rated fuse must have a particular form-factor, part number, or certification; those details are left to the SB.

• Operational grounding risk. The AD requires replacement and repair "Before further flight." That creates an immediate operational constraint: if a 20-amp fuse or damage is found, the aeroplane cannot legally continue to fly until corrected. Operators must plan for possible AOG (aircraft on ground) time and ensure availability of parts and repair support.

• Repair delegation to Raytheon. If damage is found, the AD requires contacting Raytheon for "applicable repair actions." That delegates repair authority to the manufacturer, potentially increasing turnaround time or creating dependency on manufacturer resources. The AD does not provide an alternative method of repair or an allowable deviation process in the text, so operators must be prepared to follow Raytheon’s directions.

• No record-keeping or reporting instructions in the AD. The AD does not require operators to submit completion reports to CASA, to log the work in a specific way, or to provide evidence of compliance. Operators must nevertheless retain maintenance records under general airworthiness rules (not set out in this document) and be prepared to demonstrate compliance on request. The absence of explicit recordation steps in the AD is a practical "gotcha": maintainers must bridge this gap themselves.

• Parts supply and compatibility. The AD mandates replacement with a 3-amp fuse but does not specify part numbers. Operators must ensure the 3-amp fuse used is compatible with the circuit and meets any requirements set out in SB 24-3724. Using an incorrect replacement (in form or rating) could defeat the safety objective.

• Timing pressure. The inspection must be done "Within 50 flight hours or 30 days after the effective date ... whichever occurs first." For aircraft in active service, scheduling that inspection within the shorter of those windows may necessitate rearranging flights, maintenance slots, or ferry movements.

• Cross-jurisdictional considerations. The Note referencing the FAA AD suggests parallel regulatory action overseas. For operators subject to multiple regulators (for example, international operators or those maintaining under a different authority), there may be differing compliance paperwork or timing expectations. The AD does not reconcile those requirements for the operator.

• No explicit alternative compliance route described. The AD does not set out an Alternative Method of Compliance mechanism in the text. Where operators believe an alternative approach is technically equivalent, the AD provides no guidance within the text as to whether CASA would accept such an approach and how to apply.

These operational and compliance "gotchas" are directly implied by the Directive’s language and omissions. Addressing them requires consulting Raytheon SB 24-3724 and being prepared to prove prior work, to ground aircraft if necessary, and to liaise directly with Raytheon for repair guidance.

The AD provides a compact compliance pathway. Follow these steps drawn from the Directive text.

1. Confirm applicability. Check the aircraft serial number against the AD list: "serial numbers 258541, 258556, and 258567 through 258713 inclusive." If the airframe is not on that list, the AD’s requirements do not apply as written. If it is on the list, proceed.

2. Locate the referenced documentation. Obtain Raytheon Service Bulletin SB 24-3724, dated May 2005, and review its Accomplishment Instructions. The AD specifies that both the inspection and any required replacement/repair must be carried out "in accordance with the Accomplishment Instructions of Raytheon Service Bulletin SB 24-3724, dated May 2005." Do not attempt to substitute a different procedure without prior approval from the applicable authority or the manufacturer.

3. Perform the inspection within the prescribed window. If not previously accomplished, carry out the "general visual inspection to determine if a 20-amp fuse is installed in the hydraulic over-temperature switch electrical circuit on panel ZK in the rear equipment bay" within 50 flight hours or 30 days after the AD’s effective date, whichever is sooner. The AD’s compliance timing is explicit: "Within 50 flight hours or 30 days after the effective date of this Directive, whichever occurs first."

4. Record prior compliance if applicable. If the SB actions were already completed before the AD’s effective date, retain documentation or maintenance entries demonstrating prior accomplishment so that repeated inspection or replacement can be avoided. The AD text acknowledges "If not previously accomplished" and therefore allows prior compliant actions to stand.

5. Replace any incorrect fuse before further flight. If the inspection reveals a 20-amp fuse in the specified circuit, replace it with a 3-amp fuse "in accordance with the Accomplishment Instructions of the SB 24-3724." The AD requires that replacement be completed "Before further flight after the Requirement 1 inspection."

6. Deal with signs of damage per the manufacturer. If the inspection reveals "signs of damage," contact the Raytheon Aircraft Company for "applicable repair actions and carry out the specified repairs." Do not attempt ad hoc repairs that are not authorised by Raytheon or your approved data.

7. Prepare for potential AOG. Because replacement and repair must be completed before further flight, operators should ensure access to suitable fuses and to Raytheon repair resources or approved repair schemes in order to minimise downtime.

8. Maintain records. While the AD does not state a specific reporting process, retain maintenance records, SB compliance sheets and any correspondence with Raytheon demonstrating inspection, replacement, and repair in case CASA requests evidence of compliance.

9. Coordinate with regulators if necessary. If you operate under multiple jurisdictions or if you consider an alternative method of compliance, engage CASA or the appropriate authority to seek approval. The AD does not describe an AMOC process; administrative routes will be governed by the regulator’s broader procedures not contained in this document.

10. Cross-check with FAA AD if relevant. The Note refers to FAA AD 2006-02-03. If the aeroplane is subject to FAA oversight, or if maintenance providers routinely follow FAA airworthiness directives, consult the FAA AD text to ensure aligned compliance and to avoid duplication or conflict.

11. Verify part selection and installation. Use the 3-amp fuse specified by the SB, verifying physical compatibility and rating. The AD requires replacement "with a 3-amp fuse" but leaves part identification and installation details to SB 24-3724.

12. Respect the effective date. The AD became effective on 24 February 2006; the inspection and replacement windows are calculated from that effective date when determining deadlines.

Following these steps, strictly in the order and to the extent the AD mandates, fulfils the obligations stated in the Directive text: inspect within the time window; replace any 20-amp fuse with a 3-amp fuse per SB instructions; contact Raytheon and effect specified repairs if damage is found; and do not permit further flight until corrective actions are complete.