AD/NAV/4 - Fuel System Selector Valves

Airworthiness directive (AD): A legally enforceable notice issued by CASA that requires a specific inspection, modification, or corrective action on an aircraft or component to maintain its airworthiness. Non-compliance renders the aircraft unairworthy and may ground it.

Fuel system inspection: The one-time inspection required by Requirement 1 covers the entire fuel system, including lines, pumps, vents, tanks, and selectors, using the procedures in either authorised service bulletin. This inspection is not repetitive; it is performed once only after the effective date.

Fuel selector valve inspection and functional test: Requirement 2 imposes an initial test of the fuel selector valve itself (unless replaced within the last 5 years with an approved part number) and then repeats that test every 12 months until the valve is replaced with an approved unit. The test checks for leaks, proper positioning, and correct fuel flow.

Service bulletin: A manufacturer's or specialist organisation's document that describes a recommended or mandatory modification, inspection, or repair. Here, two competing bulletins are acceptable: Sierra Hotel Aero Inc. SB 106A (the parts manufacturer) and American Navion Society Ltd. Field SB 1001 (a user group). This dual sourcing reflects some limited competition in compliance options.

Terminating action: The replacement of the fuel selector valve with one of the listed part numbers permanently ends the requirement for further 12-monthly valve tests. It does not end the one-time system inspection obligation, which must still be performed.

Effective date: The date from which compliance must be measured. Here, 28 August 2008. All time-in-service and calendar counts start from that date.

Time-in-service (TIS): Hours flown after the effective date. Compliance can be triggered by either calendar time (12 months) or flight time (100 hours), whichever comes first. This dual trigger ensures that aircraft flown infrequently are still inspected within a reasonable period.

Defect: Any finding during the inspection or test that does not meet the service bulletin's criteria. If a defect is discovered, Requirement 3 demands corrective action before further flight. The severity of defects is not further described in the AD, leaving discretion to the engineer performing the inspection.

Exclusion application (aCAR 35): For replacement valves with part numbers 145-48000-ANSI, 145-48000-ANS2, 145-48000-ANS3, or Osborne Tank Co. P/N 4090, the installation requires a separate approval from CASA under regulation 35 of the Civil Aviation Regulations 1988. This is a more expensive and time-consuming process than simply fitting a valve directly. The AD effectively limits the convenient (no-exclusion-required) replacement options to three Navion part numbers: 147-30013-201, 147-30013-202, and 147-30013-203. The other four options are available only after an exclusion approval, which imposes additional compliance costs.

Altitude correction allowance: When using Sierra Hotel Aero service information, the test pressure can be reduced by 1 inch of mercury per 1000 feet above sea level. This affects the vacuum test for valve operation and may cause confusion if the maintainer uses the sea-level standard at a high-altitude airfield.

Regulatory hierarchy: AD/NAV/4 sits under the Civil Aviation Act 1988 and the Civil Aviation Regulations 1988 (specifically regulation 37). It is a primary means of enforcing airworthiness standards.

This AD directly affects owners and operators of the listed Navion series aeroplanes registered in Australia: Models Navion (L-17A), Navion A (L-17B), (L-17C), Navion B, Navion D, Navion E, Navion F, Navion G, and Navion H. These are single-engine, four-seat aircraft originally produced in the 1940s and 1950s, now largely operated by private enthusiasts, flying clubs, and small commercial operators (e.g., aerial survey). The aircraft are ageing, so parts availability and maintenance expertise are ongoing challenges. The AD also affects licensed aircraft maintenance engineers (LAMEs) and approved maintenance organisations (AMOs) that service these types. They must be familiar with both service bulletins and the specific test procedures. The requirement to obtain an exclusion application under aCAR 35 for certain replacement valves affects not only the owner but also the engineer and the CASA office processing the application. Importers of Navion aircraft into Australia after 28 August 2008 must ensure the aircraft complies with this AD before acceptance onto the Australian register. The indirect effects extend to insurers (who may require proof of AD compliance before underwriting), future buyers (who will pay a premium for a terminated AD versus an ongoing repetitive obligation), and parts suppliers (who see demand for the approved replacement valves). The AD does not affect owners who have already replaced the valve within five years before the effective date with an approved part number, as Requirement 2 is then inapplicable initially. However, they still must perform the one-time fuel system inspection. The compliance burden falls disproportionately on owners who fly infrequently: the 100-hour threshold may take many years to reach, but the 12-month calendar deadline intervenes, forcing an inspection regardless of low utilisation. The cost of compliance includes labour (estimates would be 4-8 hours for the system inspection and valve test), parts (replacement valves range from USD 500 to USD 2,000, plus freight and import duties), and, where an exclusion application is needed, the cost of preparing and submitting that application (likely many hundreds of dollars in engineering fees plus CASA processing charges). These costs are not trivial relative to the typical market value of a Navion (often between AUD 30,000 and AUD 80,000). For some owners, the directive may tip the economics of continued operation, leading to grounding or disposal of the aircraft.

Duty to perform one-time fuel system inspection (Requirement 1): The owner or operator must ensure that the entire fuel system is inspected in accordance with one of the two service bulletins within 100 hours TIS or 12 months after the 28 August 2008 effective date, whichever occurs first. This is a one-off obligation.

Duty to perform initial valve inspection and functional test (Requirement 2): Unless the fuel selector valve has already been replaced within the five years before the effective date (or at any time afterwards) with one of the approved part numbers, the owner must cause the valve to be inspected and functionally tested within the same initial compliance period. Thereafter, the test must be repeated at intervals not exceeding 12 months until the terminating action is taken. The test must be performed using one of the two service bulletins, with altitude correction if the Sierra Hotel Aero bulletin is used.

Duty to correct defects before further flight (Requirement 3): If any defect is found during the system inspection or the valve test, the owner must take corrective action, including replacement of the valve with an approved part number if the valve itself is defective. No flight may occur until the defect is rectified.

Right to choose between service bulletins: The owner may elect to use either the Sierra Hotel Aero Inc. SB 106A or the American Navion Society Ltd. Field SB 1001. The former includes an altitude correction provision; the latter may not. This flexibility allows the owner to select the bulletin that best suits their maintenance provider's familiarity or their specific operating environment.

Right to terminate repetitive inspections: The owner may permanently stop the 12-monthly valve tests by replacing the fuel selector valve with any of the approved part numbers listed in Requirement 3. Once fitted, further tests are not required. However, the owner must still have performed the one-time system inspection (Requirement 1). This right effectively allows the owner to convert an ongoing compliance cost into a one-off capital expense.

Right to apply for exclusion approval for certain replacement valves: For the part numbers listed in the second category (Navion P/Ns 145-48000-ANSI, 145-48000-ANS2, 145-48000-ANS3, and Osborne P/N 4090), the owner may apply to CASA under aCAR 35 for approval of the proposed installation. This is a right to seek an alternative compliance path, but it is not a guarantee of approval. CASA holds discretion.

Duty to maintain records: While not explicit in the AD, the Civil Aviation Regulations require that all inspections, tests, and replacements be recorded in the aircraft's maintenance release and logbook. These records serve as proof of compliance and must be retained.

AD/NAV/4 does not itself recite penalties, but it is issued under the Civil Aviation Act 1988 and the Civil Aviation Regulations 1988 (generally regulation 37). Operating an aircraft that does not comply with an applicable airworthiness directive is an offence under the Civil Aviation Act. Penalties can include fines of up to AUD 13,750 for an individual and AUD 68,750 for a body corporate per offence, imprisonment for up to two years for serious breaches (section 20A of the Act), and administrative sanctions such as suspension or cancellation of the aircraft's certificate of airworthiness, suspension of the operator's air operator's certificate (if applicable), or suspension of the licence of the responsible maintenance engineer. CASA has broad enforcement powers including the power to issue directions to ground the aircraft, impose conditions on its operation, or require re-inspection at the owner's cost. The directive is mandatory and not a recommendation. A failure to comply during a ramp check or an annual inspection could lead to immediate action. In practice, CASA generally seeks voluntary compliance first, but repeated or deliberate non-compliance will attract stronger measures. The AD references FAA AD 2008-05-14, which may also carry enforcement consequences if the aircraft flies into US airspace or is sold to a US operator. For Australian-registered aircraft, the CASA delegate's signature on the AD gives it full force. The onus is on the owner to prove compliance. There is no grace period beyond the specified compliance times. The 12-monthly interval for valve tests is strict; any overrun renders the aircraft unairworthy until the test is done. The terminating action (valve replacement) must be recorded properly. If a replacement is done without the required exclusion approval for the valves that need it, that installation itself is non-compliant and the aircraft is unairworthy. The penalty risk is not merely financial; an accident caused by fuel starvation where the AD was not complied with could lead to civil liability and potential criminal charges for negligence.

AD/NAV/4 is issued under the Civil Aviation Act 1988 and the Civil Aviation Regulations 1988, specifically regulation 37 (Airworthiness Directives). It is a national law. It interacts with the Federal Aviation Administration's airworthiness directive system because it is explicitly based on FAA AD 2008-05-14. The note at the end of the AD states: "FAA AD 2008-05-14 Amdt 39-15408 dated 28 February 2008 refers." This means that an aircraft that is also on the US register must comply with both the FAA AD and this Australian AD. In practice, if an aircraft is dual-registered or imported from the US, compliance with the FAA AD may satisfy the Australian requirement if the actions are identical, but the operator must ensure any differences (e.g., altitude correction allowance) are addressed. The AD also interacts with CAR 35, which governs major modifications and repairs. Replacement of the fuel selector valve is considered a modification, and for certain valves the AD explicitly requires an exclusion application under aCAR 35. This imposes an additional regulatory layer beyond the AD itself. The service bulletins referenced (Sierra Hotel Aero Inc. SB 106A and American Navion Society Field SB 1001) are not themselves law but become mandatory when incorporated by reference in the AD. The AD does not directly reference the type certificate data sheet (TCDS) for the Navion models, but the basic aircraft must continue to meet its type design as approved under the Civil Aviation Safety Regulations (CASR) Part 21. Any replacement valve must be compatible with that design. The AD also interacts with the Civil Aviation Safety Regulations (CASR) Part 43 (Maintenance) and Part 91 (General Operating and Flight Rules). The operator must ensure that all maintenance is performed by authorised persons and that records are kept in accordance with CASR Part 42 or Part 91, as applicable. The AD does not supersede any earlier AD, but it may complement or be superseded by later ADs. There is no reference to state or territory laws, but workplace health and safety laws may apply to the maintenance activities themselves. The interaction with the Trade Practices Act (Competition and Consumer Act) is indirect: the AD effectively mandates the use of specified service bulletins and parts, which may restrict competition from alternative parts or procedures. However, the AD provides an alternative bulletin and a path for non-standard valves (via exclusion), so it does not create a complete monopoly. Insurance law is also relevant: an owner who fails to comply with this AD may find their hull and liability insurance voided for non-compliance with a mandatory safety requirement.

This AD has no amendment history within itself. It appears to be the original and only version of AD/NAV/4, as issued on 16 July 2008 and effective 28 August 2008. The document is a single instrument. There is no reference to any earlier proposal, draft, or superseded AD covering the same subject for these Navion models. That does not mean there were no earlier ADs for Navion fuel systems; it means this particular AD does not cite them. The absence of an amendment history means the reader must assume this is the first and current version. Any future amendments (e.g., extension of compliance time, addition of alternative parts, removal of the aCAR 35 exclusion requirement) would generate a new AD number or a revision. The AD is marked "9/2008" in the table header, which likely refers to the CASA AD series number. It is not a regulation that goes through parliamentary amendment; rather, CASA may issue a replacement AD at any time if new information emerges (e.g., a better valve design or a manufacturing fault). The lack of amendment history is typical for a single-issue AD. Practitioners should not assume the AD is static; they should check the current CASA AD database for any subsequent action.

The source text contains no reference to any litigation, administrative appeals, or court decisions related to AD/NAV/4. There is no mention of challenges to the directive, applications for review, or enforcement actions that have been litigated. This is common for a narrow technical AD affecting a small number of aircraft. The absence of litigation does not mean it has not occurred; it means the source does not provide it. In Australia, administrative review of CASA decisions (including ADs) is possible under the Administrative Appeals Tribunal (AAT) or through judicial review in the Federal Court under the Administrative Decisions (Judicial Review) Act 1977. However, such challenges are rare because ADs are safety-based and the AAT gives significant deference to CASA's technical assessment. On the US side, FAA AD 2008-05-14 may have been subject to petitions for reconsideration or legal action, but this source does not discuss that. For this deep dive, the prudent position is that no relevant Australian litigation has been identified from the given document. A current practitioner would search the AAT database and case law for "Navion" or "AD/NAV/4". The lack of litigation may indicate that the AD was accepted without controversy, or that the costs of challenging it exceed the value of the aircraft. It could also mean that most owners simply complied.

The altitude correction allowance in Requirement 1 is a potential trap. Under the Sierra Hotel Aero service information, the test standard is 24 inches of mercury at sea level, but a reduction of 1 inch per 1000 feet of altitude is allowed. If a maintenance engineer applies the sea-level standard at an airfield at 5000 feet, the test may be more stringent than intended, potentially causing unnecessary failure of a serviceable valve. Conversely, using the full reduction might allow a leaky valve to pass at high altitude. The engineer must record the altitude at which the test is performed. The American Navion Society bulletin does not appear to include this allowance, so the engineer must strictly follow the bulletin chosen without mixing standards.

The five-year lookback period for Requirement 2 is ambiguous. The phrase "unless within the last 5 years the fuel selector valve has been replaced with one of the valves specified in Requirement 3" means that owners who replaced their valve since 28 August 2003 (five years before the effective date) are exempt from the initial test. However, the AD does not define when the five-year period is measured: is it at the effective date, or at the time of compliance? The safer interpretation is that if the valve was replaced after 28 August 2003 but before the AD's effective date, the initial test is not required. But if the replacement was done after the effective date, then the owner has already taken terminating action and the test is moot anyway. The gotcha is that the valve must have been replaced with one of the approved part numbers; a replacement with a non-approved valve does not qualify for the exemption.

The terminating action requires that the replacement valve be one of the approved part numbers. However, for the four part numbers requiring aCAR 35 exclusion approval, the valve cannot be simply fitted; it must be preceded by a successful application to CASA. An owner who installs a 145-48000-ANSI valve without the approval is not complying with the AD, and the aircraft is unairworthy. The difficulty: the AD says the valve installation "will require exclusion application to CASA detailing aCAR 35 proposed installation procedure before approval for fitment can be granted." This suggests that the exclusion approval is a prerequisite to installing that valve. In other words, you cannot install the valve and then apply; you must apply first. This adds time and cost.

The one-time fuel system inspection (Requirement 1) is not terminated by replacing the valve. Owners who think that replacing the valve eliminates all obligations must remember that the initial system inspection still must be done. If they replace the valve before performing that inspection, they must still schedule the inspection within the original compliance period.

The AD uses "time-in-service" (TIS) defined as hours flown after the effective date. If the aircraft has not flown at all since 28 August 2008, the 100-hour limit never triggers, but the 12-month calendar limit does. For an aircraft that is not flown, the 12-month deadline still applies, and compliance must be achieved by 28 August 2009. An owner who stores the aircraft and ignores the AD because it is not flying will still be in non-compliance after 12 months.

The AD refers to "FAA AD 2008-05-14 Amdt 39-15408 dated 28 February 2008". Owners who also have a US-registered Navion must comply with both, and the FAA AD may have different compliance times or parts. No harmonisation is stated.

The service bulletins are dated 2007. Owners may have difficulty obtaining copies of these older documents. If they cannot locate the bulletin, they cannot comply with the AD.

The AD is signed by a delegate of CASA, James Coyne. Any challenge or request for extension must be directed to CASA. The delegate's authority is limited; a full CASA board decision might be needed for deviations.

The exclusion application requirement under aCAR 35 is not a routine administrative step. It requires engineering justification, and CASA may impose conditions or deny it. This could force the owner to use the more expensive Navion 147-30013 series valves if the exclusion is refused.

Step 1: Confirm applicability. Check the aircraft's type certificate data plate and registration documents to verify it is one of the listed models: Navion (L-17A), Navion A (L-17B), (L-17C), Navion B, Navion D, Navion E, Navion F, Navion G, or Navion H. If yes, proceed.

Step 2: Obtain a copy of the chosen service bulletin. Two options: Sierra Hotel Aero Inc. Navion Service Bulletin No. 106A (1 May 2007) or American Navion Society Ltd. Field SB No. 1001 (30 April 2007). It is advisable to use the bulletin that the maintenance engineer is most familiar with, but note the altitude correction allowance in the Sierra Hotel bulletin. Order a paper copy from the organisations or download if available.

Step 3: Perform Requirement 1 - one-time inspection of the entire fuel system. This must be done within 100 hours TIS after 28 August 2008 or within 12 months after that date, whichever comes first. The inspection covers all fuel system components (tanks, lines, pumps, filters, selector valve, drains, vents) per the bulletin. Document all findings in the aircraft maintenance records. If defects are found, go to Step 5.

Step 4: Perform Requirement 2 - initial inspection and functional test of the fuel selector valve. This is required unless the valve has already been replaced within the 5 years before 28 August 2008 or at any time since with an approved part number from Requirement 3. If the valve qualifies for the exception, skip to Step 6 (but still do Step 3). If not, perform the test per the bulletin. For Sierra Hotel bulletin users, apply the altitude correction if testing above sea level. Record the test date, results, and altitude used. This test must be repeated every 12 months until the terminating action is taken. Mark the next due date in the aircraft's inspection schedule.

Step 5: Correct defects (Requirement 3). If any defect is found in Step 3 or Step 4, you must rectify it before further flight. For a defective fuel selector valve, replace it with one of the following part numbers: Navion 147-30013-201, 147-30013-202, or 147-30013-203 (no further approval needed). Alternatively, you may replace with Navion 145-48000-ANSI, 145-48000-ANS2, 145-48000-ANS3, or Osborne Tank Co. 4090, but only after obtaining a CAR 35 exclusion approval from CASA. This involves submitting a proposed installation procedure to CASA detailing the engineering basis, any modifications, and demonstrating that the alternative valve provides at least an equivalent level of safety. CASA will assess and either approve or reject. Do not install these valves before receiving written approval. Once the valve is replaced with an approved part number, record the installation and terminate the 12-monthly test requirement (see Step 6).

Step 6: Manage the terminating action. If the replacement valve is one of the approved types (including those requiring aCAR 35 approval), then the repetitive valve tests (Requirement 2) are permanently terminated. The one-time system inspection of Requirement 1 is already done and not repeated. However, note that if the valve was replaced within 5 years before the effective date, the terminating action is automatically in effect from the start, so no initial test was needed. Still, you must verify that the replacement actually was with an approved PN and that the installation was properly recorded.

Step 7: Maintain records. Keep all maintenance entries, copies of the service bulletin used, test results, and, if applicable, the CAR 35 exclusion approval letter in the aircraft's logbook or maintenance release. The AD does not specify record retention, but standard practice is to keep records for the life of the aircraft.

Step 8: Monitor ongoing compliance. If you have not taken terminating action, ensure the 12-month valve test is performed every year and recorded. Do not let the interval lapse.

Step 9: For new owners or after sale: Transfer all AD compliance records to the new owner. The AD remains with the aircraft. A buyer should verify that either the terminating action has been taken (and a receipt for the approved valve is available) or that the next valve test is within the 12-month cycle.

Step 10: Seek professional help. AD/NAV/4 is technical. Use a licensed aircraft maintenance engineer with Navion experience. The aCAR 35 exclusion application benefits from an experienced aviation engineer or consultant. CASA's website provides guidance on airworthiness directive compliance.