AD/F100/71 - Main Landing Gear Bay Fuel/Hydraulic Lines

Several key concepts underpin this airworthiness directive. Airworthiness directive (AD): a legislative instrument issued by CASA under Part 39 of the Civil Aviation Safety Regulations (though the source text does not cite that Part, it is the conventional legal basis). An AD identifies an unsafe condition that exists or is likely to exist on a type design and mandates corrective action to restore safety before further flight or within a specified period. Fuel lines and hydraulic lines: the components in the main landing gear (MLG) bay that route fuel and hydraulic fluid, respectively. The background section explains that during aircraft manufacture a minimum clearance of 3 mm was maintained between them, but operational loads or maintenance tasks can reduce that distance, causing interference. Clearance measurement: the physical gap between the two lines, measured in millimetres. The AD sets 3 mm as the threshold. If the gap is at least that value, the risk of contact is deemed acceptable. Below that threshold, contact is likely under normal loads. Chafing marks: physical evidence of wear on the fuel line caused by rubbing against the hydraulic line. The presence of chafing indicates that interference has already occurred, compromising the fuel line’s integrity and creating an immediate leak risk. The AD distinguishes between cases with and without chafing because the former demands immediate replacement (before further flight) while the latter only requires readjustment within six months. Service bulletin (SB): a manufacturer’s recommended modification or inspection procedure. Here, Fokker Service Bulletin F100‑28‑041 provides the specific steps. The AD makes compliance with that SB mandatory, but only to the extent adopted by CAA‑NL approval. The AD notes that CAA‑NL AD NL‑2005‑010R1 and EASA approval No. 2005‑6232 underpin the directive, showing a chain of international regulatory acceptance. Main landing gear (MLG) bay: the compartment in the wing or fuselage that houses the retracted landing gear. In this aircraft type, fuel and hydraulic lines pass through that bay in proximity to hot brakes, making a fuel leak a fire hazard. The concept of one‑time inspection means the check is not recurring unless a later AD or maintenance requirement re‑imposes it. However, if an operator modifies the line attachments as per the corrective actions, those modifications become part of the aircraft’s approved maintenance data.

The primary persons and entities affected are operators of Fokker F28 Mark 0070 and Mark 0100 aeroplanes. This includes airlines, charter operators, and any entity holding an Australian air operator’s certificate that operates such aircraft. Because the Fokker 100 is a commercial jet typically used in short‑to‑medium‑haul operations, the affected operators are likely to be regional airlines, leasing companies, or government flight departments. Maintenance organisations (approved maintenance organisations or AMOs) are also directly affected. They must perform the inspection and any corrective actions in accordance with the Fokker Service Bulletin and record the results in the aircraft’s maintenance records. The AD imposes a duty on the holder of the airworthiness certificate (the operator) to ensure compliance, but in practice the maintenance organisation will execute the work. CASA itself is affected as the issuing and enforcement authority. It must monitor compliance, review maintenance records on request, and take enforcement action if the AD is not met. The manufacturer, Fokker Aircraft B.V. (now part of what was once Stork Aerospace), is indirectly affected because its service bulletin becomes mandatory law through the AD. Any later revision approved by CAA‑NL automatically updates the compliance method. Passengers and the public are affected in a diffuse sense: the AD’s purpose is to prevent a main landing gear bay fire caused by fuel leaking onto hot brakes. Reduced fire risk benefits all who fly on or near these aircraft. However, the AD also imposes costs that may flow through to ticket prices or service availability. Insurance underwriters may take an interest, because non‑compliance could affect liability coverage. The AD also has an international dimension: because the Fokker 100 was manufactured in the Netherlands and is operated in many jurisdictions, this Australian AD aligns with the European Aviation Safety Agency (EASA) approval, affecting global operators that bring aircraft into Australian airspace. Foreign operators of Australian‑registered aircraft are equally bound.

The principal duty is on the operator (or the holder of the certificate of airworthiness) to carry out the one‑time inspection within six months after 27 October 2005. This duty is absolute: the AD does not allow extensions or alternative means of compliance unless approved by CASA. The operator must ensure the inspection is performed in accordance with the accomplishment instructions in Part 1 of Fokker SB F100‑28‑041. If the clearance between fuel and hydraulic lines is 3 mm or more in both MLG bays, the duty is satisfied and no further action under this AD is required. The aircraft may be returned to service immediately. If the clearance is less than 3 mm, two sub‑duties arise. Duty (a): if chafing marks are found on the fuel line, the operator must before further flight replace the affected fuel line and modify or readjust the attachment of both lines per Part 2 of the SB. This is an urgent duty because a fuel leak could cause a fire on the next landing. Duty (b): if no chafing marks are found but clearance is still less than 3 mm, the operator must modify or readjust the attachment within six months of the inspection. This deferred duty allows the aircraft to continue in service temporarily, but the modification must be completed within the window. The operator also has the right to use a later revision of the service bulletin approved by CAA‑NL. This provides flexibility if the manufacturer refines the corrective action. However, the operator cannot unilaterally use an unapproved revision; it must be endorsed by CAA‑NL. The AD also confers a right on the operator to return the aircraft to service after completing the inspection (if clearances are adequate) or after the corrective actions. The AD does not require repeated inspections; it is a one‑time action. After compliance, the only ongoing duty is to keep the maintenance records demonstrating compliance. The AD does not create any private right of action for passengers or third parties; enforcement is through CASA’s regulatory powers.

The source text itself does not prescribe specific penalties, but as an airworthiness directive issued under the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations, non‑compliance is a breach of those laws. Under s 20A of the Civil Aviation Act, a person who contravenes an airworthiness directive is guilty of an offence punishable by a fine of up to 50 penalty units for an individual or 250 penalty units for a body corporate (the exact amount depends on the penalty unit rate at the time). Additionally, CASA can suspend or cancel the certificate of airworthiness of an aircraft that is not maintained in accordance with an AD. That effectively grounds the aircraft until compliance is achieved. In practice, CASA’s enforcement approach involves surveillance: inspectors may audit maintenance records and physically inspect aircraft. If non‑compliance is found, CASA can issue a direction to comply, impose a civil penalty, or prosecute. The AD’s distinction between “before further flight” and “within six months” creates two compliance deadlines. Failure to comply with the “before further flight” requirement is treated as a serious and immediate safety risk, likely inviting swift enforcement action. The AD also notes that it was based on a prior Dutch AD and EASA approval, meaning that Australian operators are subject to essentially the same obligations as those in Europe, reducing the scope for regulatory arbitrage. The enforcement burden falls on operators to self‑monitor and document. The AD does not require CASA to be notified of compliance unless requested, but maintenance records must be available for inspection. If an operator fails to keep adequate records, that is a separate offence. The enforcement regime is thus a mix of prescriptive deadlines and post‑action verification. The 2005 effective date means historical non‑compliance could still be pursued within applicable limitation periods, but practically most operators would have complied long ago. For current aircraft still operating, ongoing compliance is a condition of continued airworthiness.

This AD operates within a hierarchy of Australian aviation safety legislation. The primary enabling law is the Civil Aviation Act 1988, which empowers CASA to issue airworthiness directives. The Civil Aviation Safety Regulations 1998 (CASR), particularly Part 39, govern the process for issuing and complying with ADs, though the source text does not cite them explicitly. The AD also interacts with international regulatory instruments: the European Aviation Safety Agency (EASA) approval No. 2005‑6232 is referenced in a note, indicating that this Australian AD is accepted as equivalent to the European directive. This matters for aircraft that are operated in multiple jurisdictions; compliance with the Australian AD will generally satisfy similar requirements in EASA member states. Conversely, if an aircraft is imported from Europe and already complied with the Dutch AD, that compliance may be recognised by CASA as meeting this AD, provided the actions were identical. The AD does not override other ADs that may apply to the same aircraft for different defects. An operator must comply with all applicable ADs, and the cumulative burden is assessed separately. The AD also refers to Fokker Service Bulletin F100‑28‑041, which is not law but is incorporated by reference. The AD makes compliance with that SB mandatory, so any later revision approved by CAA‑NL automatically updates the legal requirement without a new AD being issued. This is a form of dynamic incorporation. The AD also interacts with the aircraft’s approved maintenance program (AMP). Typically, an AMP includes recurring tasks; this AD imposes a one‑time task that should be recorded in the AMP logbook. Once completed, it may affect future maintenance intervals if the corrective actions (e.g., line replacement) require periodic checks under other instructions. There is no conflict with the Australian Consumer Law; the AD is a safety regulation, not a consumer protection rule. Operationally, the AD interacts with Civil Aviation Order 100.6, which requires operators to maintain aircraft in accordance with approved data. The AD constitutes approved data. Failure to comply with the AD is a breach of that order as well.

The source text provides no explicit amendment history for AD/F100/71 itself. The effective date is given as 27 October 2005, and the document appears to be the original issuance. However, the note refers to CAA‑NL AD NL‑2005‑010R1, where “R1” indicates revision 1 of the Dutch directive. That suggests the Dutch original was amended before the Australian AD was issued. The Australian AD is therefore based on the revised version. The source text also mentions “or later CAA‑NL approved revision” regarding the service bulletin, meaning the compliance method can evolve without amending the AD. As for the AD itself, a search of CASA’s AD database (not provided here) would reveal whether AD/F100/71 has been superseded, reissued, or cancelled. Given that the Fokker 100 is an older aircraft type now largely out of commercial production, many structural and system ADs have been superseded by terminating actions or fleet‑wide modifications. It is plausible that AD/F100/71 has been superseded by a later AD that mandates a permanent modification to relocate or re‑route the lines, making the one‑time inspection redundant. However, the source does not indicate any such supersession. The AD number “11/2005” suggests it was the eleventh AD for this aircraft type in 2005. The document itself shows the same AD number multiple times (AD/F100/71) with duplicate headings, suggesting formatting artefacts rather than multiple amendments. The signature by James Coyne as Delegate of CASA is dated 15 September 2005, which is before the effective date. No other versions are listed. For deep‑dive purposes, we can only state what the source shows: the AD was issued in 2005, effective from 27 October 2005, with no textual amendments reproduced. The appearance of “AD/F100/71 AD/F100/71” in the header may be a duplication error in the source but does not indicate multiple amendments.

The source text does not mention any litigation concerning this specific airworthiness directive. There is no reference to court cases, tribunal appeals, or challenges to the AD’s validity. This is unsurprising, as airworthiness directives are typically uncontested in court. Operators rarely litigate because the safety argument is strong, the cost of compliance is relatively low compared to litigation expense, and CASA has wide discretion. However, we can infer from general Australian aviation law that an operator could theoretically seek judicial review under the Administrative Decisions (Judicial Review) Act 1977 if it could show the AD was procedurally flawed, ultra vires, or based on an error of fact. No such challenge is recorded in the source. Enforcement proceedings may have occurred if an operator failed to comply, but again no case is named. A practical search of the Australasian Legal Information Institute (AustLII) might reveal enforcement actions under s 20A of the Civil Aviation Act for breach of an AD, but those would be general cases not specific to AD/F100/71. Because the AD targets a specific fleet that has largely retired from active service in Australia, the likelihood of litigation is low. The AD itself is relatively simple and unambiguous, reducing interpretive disputes. The background section provides a clear factual basis for the need: a fuel leak caused by chafing. That evidence would be hard to rebut in court. The only plausible litigation scenario would be a dispute over whether a particular operator actually complied (e.g., whether the clearance was measured correctly, or whether chafing marks existed but were ignored). Those would be factual disputes in enforcement proceedings, not a challenge to the AD’s validity. In any event, the source provides no data, so the deep dive must note the absence of named litigation while acknowledging the potential for enforcement‑related cases.

Several subtleties in this AD can trap unwary operators, maintenance engineers, or compliance officers. 1. The 3 mm threshold is measured between the fuel and hydraulic lines, not between other components. An operator might inadvertently measure clearance to a different structure (e.g., a bracket or wire bundle) and assume the lines are safe. The AD specifically requires clearance between those two line types. 2. The inspection must follow Part 1 of the service bulletin, but Part 1 may specify a particular measurement technique (e.g., using feeler gauges at specific points). Deviating from that technique could produce incorrect readings and lead to a false conclusion of compliance or non‑compliance. 3. The AD applies to both LH and RH MLG bays. An operator who inspects only one side and finds adequate clearance might assume the other side is fine. The AD requires separate measurement in each bay. 4. The distinction between “chafing marks on the fuel lines” and “no chafing marks” is critical. Chafing marks may be hidden under hose clamps or behind other lines. A cursory visual check might miss them. The AD requires the fuel line to be examined for wear; if any mark is present, the more stringent action (before‑further‑flight replacement) applies. 5. The compliance timeline has two different deadlines: the inspection itself is due within 6 months from 27 October 2005. If corrective action (b) applies (readjustment without chafing), the deadline is 6 months from the inspection, not from the effective date. Operators must track both dates. 6. The AD says “when clearances … are found of 3 mm or more in both MLG Bays, no further action is required.” That means if one bay is 3 mm and the other is below, corrective action is required for the low‑clearance bay. Do not assume symmetry. 7. The service bulletin is incorporated by reference, but the AD allows “later CAA‑NL approved revision.” An operator cannot use a revision approved only by EASA or another regulator; it must be CAA‑NL specific. 8. The AD does not require a recurring inspection. However, the corrective actions (especially readjustment) may alter the line attachment and could introduce new stress concentrations. The operator should consider whether those modifications create ongoing inspection requirements under other maintenance instructions. 9. The AD is titled “Main Landing Gear Bay Fuel/Hydraulic Lines” and includes a note about EASA approval. Operators may mistakenly think compliance is optional if they are not in Europe. It is not; it is an Australian AD. 10. Finally, the AD was issued in 2005. For aircraft still on the Australian register, the one‑time inspection should have been completed long ago. But if an aircraft was imported later without evidence of prior compliance, the new operator must ensure the action was done. Relying on an incomplete maintenance history could be a costly oversight.

Compliance with AD/F100/71 involves a discrete, step‑by‑step process that should be documented meticulously. Step 1: Obtain the latest CAA‑NL approved revision of Fokker Service Bulletin F100‑28‑041 (Parts 1 and 2). As at the effective date, the revision was 20 July 2005, but a later revision may be used if approved. Step 2: Schedule the inspection within six months of 27 October 2005, i.e., by 27 April 2006. For aircraft that enter the Australian register after that date, the inspection must be accomplished before further flight or within a timeframe agreed with CASA (though the AD does not expressly provide for this, best practice is to treat the AD as applicable immediately). Step 3: Perform the inspection in accordance with Section 3 of the accomplishment instructions, Part 1. This likely requires accessing the LH and RH MLG bays, locating the fuel and hydraulic lines, and measuring the clearance using an appropriate tool (e.g., feeler gauge or dial caliper). Pay attention to the specific points specified in the SB; measure at the closest approach between the lines. Step 4: Record the measured clearance for each bay. If both clearances are 3 mm or greater, note that the AD is complied with, and the aircraft may be returned to service. No further action under this AD is required. Step 5: If either bay has a clearance below 3 mm, assess for chafing marks on the fuel line. A bore scope or mirror may be needed to inspect hidden surfaces. Step 6a - chafing present: Immediately replace the affected fuel line with a new or serviceable part. Then modify or readjust the attachment of both fuel and hydraulic lines as per Part 2 of the SB. The aircraft cannot fly again until this is complete. Step 6b - no chafing: Modify or readjust the attachment per Part 2 within six months of the inspection date. The aircraft may continue in service during that period. Step 7: Ensure all work is performed by an appropriately authorised maintenance engineer and that the maintenance release is correctly signed. Step 8: Update the aircraft’s maintenance records to show compliance: include the AD number, the SB revision used, the date of inspection, measured clearances, any corrective actions taken, and the signature of the person who accomplished the work. Keep the record for the life of the aircraft (or at least the period required by CAR 42). Step 9: If the required parts (fuel lines) are not available, contact Fokker or its successor for approved alternatives; CASA may issue an alternative means of compliance in extreme cases. Step 10: For ongoing operation, be aware that the corrective actions may have altered line routing. Check for any new interference points or stresses. While the AD does not mandate a repeat inspection, prudent operators might include a periodic check in their maintenance program, especially if the aircraft operates in a high‑vibration environment.