AD/LEARJET 35/32 Amdt 1 - Tip Tank Flapper Valves

Tip tank flapper valve. A flapper valve is a one‑way or check valve located inside the fuel tip tank on each wing of the Learjet 35/36. Its function is to allow fuel to flow out of the tip tank but prevent fuel from flowing back in, or to maintain proper fuel sequencing. The condition of the flapper is critical for balanced fuel distribution. The directive specifically concerns “both flappers of the tip tank in each wing”, meaning there are two flappers per tip tank, so four flappers total per aeroplane.

Deterioration. The directive requires an inspection to detect “cracks, cuts, breaks, splits, or warpage” of each flapper. These physical faults can prevent the flapper from seating properly against its tube, allowing fuel to cross‑feed unevenly. The inspection must be performed in accordance with Learjet Service Bulletin SB 35/36‑28‑10, dated 6 October 1995.

Part numbers and terminating action. The central innovation of Amendment 1 is the introduction of a part‑number‑based terminating action. The older parts, flapper P/N 2323006‑5 and flapper assembly P/N 2323006‑6, are no longer acceptable for continued service. They must be replaced with the new parts: flapper P/N 2323006‑802 and flapper assembly P/N 2323006‑801. The new parts can be identified by the raised letters and numbers “S‑461” on the convex side of the flapper. If an aeroplane already has all four flappers of type 2323006‑802 and all four assemblies of type 2323006‑801, then the aeroplane has achieved “terminating action” and the repetitive inspections required by Requirements 1 and 4 of the directive can be stopped. Replacement of any older part with the new part also stops the repetitive inspections.

Repetitive inspections. Under the original directive, operators were required to inspect the flappers for deterioration every 600 hours time‑in‑service. This cycle was indefinite. Amendment 1 offers a way out of that cycle, but only by verifying the part numbers and, if necessary, upgrading to the current standard.

Service bulletins. The directive relies on two service bulletins for accomplishment instructions: Learjet SB 35/36‑28‑10 (original, 6 October 1995) for the inspection and replacement steps, and Bombardier SB 35/36‑28‑10 Revision 2 (9 May 2001) for the replacement of the older flapper or assembly with the new part. Operators must use these bulletins as the authoritative technical procedures; the directive does not reproduce the detailed steps.

Compliance times. The directive uses several time frames: hours time‑in‑service (TIS) since installation or since last replacement; calendar time (e.g., 5 years, 90 days); and a combination. For the terminating inspection (Requirement 5), the compliance time is “within 600 hours time‑in‑service since last replacement of any flapper valve in accordance with the requirements of this Directive, or within 90 days after the effective date of this Directive, whichever occurs later.” This gives operators a window but with a hard 90‑day cap from the effective date. For aeroplanes where the age or TIS of the flapper valve cannot be determined, the original directive had required immediate replacement (within 50 hours after 29 February 1996) and that requirement remains unchanged.

The directive applies to all Gates Learjet Model 35 aeroplanes with serial numbers 35‑002 through 35‑676 inclusive, and Model 36 aeroplanes with serial numbers 36‑002 through 36‑063 inclusive. This covers the entire production run of these models that could be registered in Australia or operated under an Australian certificate of airworthiness. The primary affected parties are the registered owners and operators of those aircraft. For an owner‑operator flying a single aircraft, the compliance burden includes the cost of the inspection (labour, possible borescope or access equipment), the cost of replacement parts if needed (each flapper and assembly may cost several hundred to over a thousand dollars), and the opportunity cost of downtime while maintenance is performed. For fleet operators, the cost multiplies. The directive also affects maintenance organisations (MROs) that carry out the work. They must have access to the service bulletins, the correct parts, and appropriately trained and authorised engineers. The directive does not impose any explicit training requirement, but the requirement to follow the service bulletins implies that the person performing the work must be competent to interpret the bulletin and conduct the inspection and replacement.

Accountants and compliance managers must ensure that the directive is incorporated into the operator’s continuing airworthiness management system. The aviation regulations likely require that ADs be tracked by part number, serial number effectivity, and compliance status. This directive introduces a terminating action that, once recorded, can simplify future tracking. However, the records review option means that an operator may avoid a physical inspection if maintenance records conclusively show the part numbers. This could save cost, but the operator must be confident the records are accurate and complete. The directive does not state who must determine conclusiveness; it says “acceptable if the P/N of the flappers and flapper assemblies can be conclusively determined from that review.” The burden is on the operator or maintainer to be satisfied.

The directive also affects sellers of parts: Requirement 6 prohibits installing a flapper with P/N 2323006‑5 or an assembly with P/N 2323006‑6 on any aeroplane. Any stock of those parts must not be used on these aircraft, and any new installation will require the current part numbers. That may strand inventory of older parts unless they can be used on other aircraft not covered by this directive.

Duty to inspect and replace. The core duty is to comply with Requirements 1 through 6 of the directive. This includes performing the deterioration inspection (Requirement 1) according to SB 35/36‑28‑10, replacing both flappers in each wing with new flappers per the bulletin (Requirement 2), and, for aeroplanes with unknown flapper history, performing that replacement (Requirement 3). After any replacement, another inspection must be accomplished (Requirement 4). Additionally, a part‑number determination must be made within the compliance time of Requirement 5. If the part numbers are not the terminating ones, the older parts must be replaced per Bombardier SB 35/36‑28‑10 Revision 2. Finally, no installation of the prohibited parts is allowed (Requirement 6).

Duty to use specified service bulletins. The directive does not prescribe the detailed steps; it mandates that the actions be done “in accordance with” the listed service bulletins. This makes the bulletins legally binding for the purposes of compliance. Operators must obtain the correct revision of each bulletin. Using an older revision or a different method may not satisfy the requirement and could expose the operator to enforcement action.

Right to terminate repetitive inspections. The directive grants a valuable right: once the operator has verified (through inspection or records review) that the aeroplane is equipped with flappers P/N 2323006‑802 and assemblies P/N 2323006‑801, no further repetitive inspections under Requirements 1 and 4 are required. Similarly, if any older parts were replaced with the new ones, the repetitive inspections stop. This provides a permanent compliance out and reduces long‑term maintenance burden. However, the operator must ensure that the work is documented and that the achievement of terminating action is recorded. The directive does not prescribe the form of record, but normal practice would be a maintenance release or a logbook entry.

Right to use records review. Instead of physically inspecting the flappers to determine part numbers, the operator can review the aeroplane maintenance records. This right is conditional: the review must conclusively establish the part numbers. Records that are ambiguous, incomplete, or that conflict with physical evidence may not be acceptable. The operator bears the risk: if a later physical inspection reveals a different part number, the records review was not conclusive and the operator may be non‑compliant from the date of the review.

No right to deviate without approval. The directive does not contain an explicit alternative means of compliance (AMOC) provision, but general aviation regulatory schemes such as CASR Part 39 typically allow CASA to approve AMOCs separately. Operators wishing to deviate from the directive (e.g., by using a different inspection method) would need to seek CASA approval before the deviation. The directive itself does not grant any self‑authorised flexibility. Because the directive originated from FAA AD 2005‑16‑09, any FAA‑approved AMOC might be recognised by CASA under bilateral agreements, but that is not stated in the source.

The directive itself does not list penalties, but it is issued by a delegate of CASA under the Civil Aviation Safety Regulations 1998 (CASR), specifically Part 39 which deals with airworthiness directives. Under CASR Part 39, compliance with an AD is mandatory. Failure to comply is a breach of the regulations and can attract enforcement action including the imposition of civil penalties, suspension or cancellation of certificates of airworthiness, grounding of the aircraft, and prosecution in serious cases. The exact penalty amounts are not specified here, but under the civil aviation legislation, maximum penalties for non‑compliance with an AD can be significant, often involving penalty units. For a corporation, penalties can reach hundreds of thousands of dollars. For an individual, the regulatory framework typically imposes fines and possible imprisonment for reckless conduct. In practice, CASA’s enforcement policy often starts with a notice of non‑compliance and a demand for rectification, but persistent or deliberate non‑compliance can escalate.

The directive is backstopped by the requirement that the aeroplane must remain airworthy. An aircraft that is not in compliance with applicable ADs cannot legally fly. Any person who operates or permits the operation of a non‑compliant aircraft may be liable. Maintenance organisations that sign off work as compliant when it is not may also face action under their certifications.

The amendment’s effective date is 27 October 2005. The compliance times for Requirement 5 are measured from that date (90 days) or from the last flapper replacement. An operator who fails to meet the compliance time will be in contravention. Because the directive is now over 18 years old, almost all affected aircraft would have been subject to it for many years. However, if an aircraft was imported after 2005 or if a previous owner obtained deviation, the current operator must still ensure compliance. The directive does not sunset; it remains in force until superseded or withdrawn.

No specific enforcement actions or court cases are referenced in the source. The directive is a routine safety measure, and litigation is rare for maintenance‑type ADs unless a dispute arises over liability for a crash or over the validity of the directive. The absence of cited litigation suggests the industry has generally complied without court contest.

The directive explicitly references FAA AD 2005‑16‑09 (Amendment 39‑14214). The FAA AD is the United States equivalent directive, issued by the Federal Aviation Administration. The CASA directive is a “mirror” AD, meaning that CASA has determined that the same unsafe condition exists on Australian‑registered aircraft and that the same corrective action is required. Under the bilateral airworthiness agreements between the United States and Australia, compliance with the FAA AD may be considered compliance with the CASA AD if the operator holds an FAA‑issued airworthiness certificate. However, for Australian‑registered aircraft, the CASA directive is the legally enforceable instrument. The cross‑reference indicates that the technical content (service bulletins, part numbers, compliance times) is harmonised. In practice, an Australian operator using a U.S. maintenance provider should confirm that the work meets both ADs, or at least the applicable one.

The directive also interacts with the continuing airworthiness requirements under CASR Part 42 (Continuing Airworthiness) and Part 145 (Maintenance Organisations). The operator must incorporate the AD into their maintenance program and must ensure that any maintenance organisation they use is capable of performing the required inspections and replacements. The records review option interacts with the requirement to keep accurate maintenance records under CASR Part 42. If records are lost or incomplete, the operator may be forced to perform a physical inspection, increasing cost.

Additionally, the directive interacts with the Australian Transport Safety Bureau (ATSB) reporting requirements. If during the inspection a defect is found that meets the definition of a reportable safety matter (e.g., a cracked flapper that could have caused an accident), the operator may need to report it under the Transport Safety Investigation Act.

There may also be interactions with international operations. If an Australian‑registered Learjet 35 operates overseas, it must comply with the airworthiness directives of the state of registry (Australia) and also with the local regulations of the state being flown over. However, most states recognise CASA ADs. The part numbers and repetitive inspection regime are typical of many national ADs.

The directive does not reference any other Australian legislation or standards. It is a stand‑alone regulatory instrument.

The original issue of AD/LEARJET 35/32 (no amendment number) became effective on 29 February 1996. That original directive required repetitive inspections of the tip tank flappers for deterioration and mandatory replacement after five years or 2,400 hours time‑in‑service, plus repetitive inspections after replacement. The compliance times were measured from the effective date or from installation.

On 15 September 2005, James Coyne, a delegate of CASA, signed Amendment 1. The amendment became effective on 27 October 2005. The key change introduced by the amendment is the addition of a one‑time part‑number determination (Requirement 5) that, if the correct parts are found, ends the repetitive inspections under Requirements 1 and 4. The amendment also prohibits the installation of older part numbers (Requirement 6). The source does not list any other amendments. The background states that this amendment was prompted by “numerous continual inspections” and the approval of a new, improved flapper and flapper assembly. This suggests that the original design was less durable or harder to maintain, and that the industry had been pushing for a terminating solution. The amendment also aligns with the FAA’s AD 2005‑16‑09.

There is no mention of any prior amendments between 1996 and 2005. It is possible that there were none, or that they are not recorded in the provided text. The directive remained in force as Amendment 1 as of the 2005 date.

The source does not record any litigation concerning this specific Airworthiness Directive. The directive is a maintenance‑type instrument, and disputes over such directives are uncommon in Australian aviation law. Operators generally comply to maintain their aircraft’s airworthiness certification. Any legal challenge would likely arise only if an operator believed the directive was ultra vires, procedurally flawed, or imposed unreasonable costs without sufficient safety justification. There is no evidence of such challenge in the public domain relevant to this instrument.

Enforcement actions under the AD might have been handled administratively, and a court case could have arisen from a crash attributed to flapper valve failure, but the directive’s purpose is to prevent that failure. If a crash did occur and the aircraft was not in compliance, the litigation would likely focus on the operator’s failure to comply rather than on the validity of the directive. The directive itself is over 18 years old and well established; challenge risk is very low.

Because the source provides no information on litigation, the deep dive can only note its absence. This is consistent with the instruction to name only cases the source names.

Several aspects of the directive can trap an unwary operator or compliance professional.

The part‑number determination can be done by records review, but the directive says “conclusively determined”. If records show a flapper was replaced but the entry does not include the part number, or if there are entries for multiple part numbers, the review is not conclusive and a physical inspection will be required. A records review that later proves wrong (because the records were inaccurate) puts the operator in non‑compliance retroactive to the date the review was relied upon. Therefore, relying on records may carry residual risk.

The interaction between the original repetitive inspections and the new terminating action is nuanced. Requirement 4 says: “Within 600 hours time‑in‑service following replacement of any flapper valve in accordance with the requirements of this Directive, and thereafter at intervals not to exceed 600 hours time‑in‑service, inspect the flappers…”. This requirement remains in effect until it is terminated. The terminating action is only achieved through Requirement 5 (part‑number inspection) or by having the correct parts installed. An operator who merely replaces a flapper under Requirement 2 or 3 must still perform the repetitive inspection under Requirement 4 within 600 hours of that replacement. But then Requirement 5 says that the part‑number inspection must be done within 600 hours since last replacement OR 90 days after effective date, whichever later. If the operator replaces a flapper after the effective date, the clock for Requirement 5 starts from that replacement. The operator might inadvertently skip the Requirement 4 inspection if they think the replacement automatically terminates it. It does not. Only the part‑number verification does.

The compliance time for Requirement 5 uses “since last replacement of any flapper valve in accordance with the requirements of this Directive.” That language could be ambiguous: does it mean replacement per the original directive or per the amendment? The directive says “in accordance with the requirements of this Directive”, which would include both old and new requirements. So a replacement done under the original directive in, say, 1998 counts. Then the 90‑day cap applies: within 90 days after 27 October 2005 or 600 hours since that 1998 replacement, whichever occurs later. An operator whose last replacement was in 1998 might have already accumulated well over 600 hours since that replacement, so the later of the two times would be 90 days after effective date (27 October 2005 plus 90 days = 25 January 2006). But if they are at 2,000 hours since last replacement, the 90‑day cap overrides a much tighter 600‑hour window? Actually the phrase “whichever occurs later” means the later of the two dates: 600 hours TIS since last replacement OR 90 days after effective date. If 600 hours TIS will be reached after the 90 days, then the compliance time is that later date. But if 600 hours TIS was already passed many years ago, the 90‑day date is the later date, so the operator has until 90 days after effective date. That gives a decent window. However, if the operator replaced flappers after the effective date, the 600‑hour TIS might be the later date. So careful calculation is needed.

The replacement parts themselves may have different ordering and stocking issues. The directive requires use of Bombardier Service Bulletin SB 35/36‑28‑10 Revision 2, dated 9 May 2001. Operators must ensure they have that specific revision, not an earlier or later one without checking compatibility. The parts themselves are proprietary and may have long lead times. A small operator may struggle to source the parts within the 90‑day deadline if a physical inspection reveals the old parts at day 89.

A subtle gotcha: an operator who physically inspects the flappers for deterioration (Requirement 1) and finds no deterioration must still check part numbers under Requirement 5. The absence of deterioration does not mean the part numbers are the terminating ones. The old P/N 2323006‑5 flappers may be in good condition but are non‑compliant. So the operator cannot simply rely on a clean inspection report; they must follow the part‑number verification.

Finally, the directive is signed by a delegate of CASA. The signature block includes a reference to the FAA AD. This is a procedural gotcha: if the directive is challenged on the basis of delegation, the signature appears to be valid, but operators should note that the effective date is 27 October 2005, and compliance dates run from that date. Any work done before the effective date could not be used to satisfy Requirement 5 unless the directive’s compliance time specifically allows pre‑effective compliance (it does not state that, but the “within 600 hours TIS since last replacement” could include replacements done before the effective date). The start point for Requirement 5 is not the effective date but the last replacement date.

Compliance with AD/LEARJET 35/32 Amdt 1 involves a sequence of steps that must be followed carefully.

1. Determine applicability. Verify that the aeroplane is on the affected list: Model 35, serial numbers 35‑002 to 35‑676 inclusive; Model 36, serial numbers 36‑002 to 36‑063 inclusive. If the aeroplane is not within these ranges, the directive does not apply. If it is, proceed.

2. Gather maintenance records. Obtain the complete maintenance history for the tip tank flapper valves on both wings. Look for entries showing installation of flappers and flapper assemblies, including part numbers. Specifically, you need to identify the part number of each flapper (P/N) and each flapper assembly (P/N). Note that the flapper assembly part number is separate from the flapper part number. The acceptable terminating combination is flapper P/N 2323006‑802 and flapper assembly P/N 2323006‑801. The prohibited older parts are flapper P/N 2323006‑5 and flapper assembly P/N 2323006‑6.

3. Perform a records review or physical inspection. If the maintenance records conclusively show that all four flappers are P/N 2323006‑802 and all four assemblies are P/N 2323006‑801, you can stop. No further action is required under this directive, and you may cease the 600‑hour repetitive inspections. Document this finding in the aircraft logbook or continuing airworthiness record.

4. If records are inconclusive or identify older parts. If records are missing, ambiguous, or show the older part numbers, you must physically inspect the flappers. The flappers can be identified by the raised letters and numbers “S‑461” on the convex side. If you find any flapper that does not have “S‑461”, it is likely an older version. The physical inspection must also assess deterioration as per Requirement 1 if you are still within the repetitive inspection interval. However, for the part‑number determination, you only need to read the part numbers.

   • If you find all flappers and assemblies are the terminating types, no further mandatory action is needed (same as step 3).
   • If you find any flapper P/N 2323006‑5 or assembly P/N 2323006‑6, you must replace that component with a new flapper (P/N 2323006‑802) or new assembly (P/N 2323006‑801) as applicable. The replacement must be performed in accordance with the Accomplishment Instructions of Bombardier Service Bulletin SB 35/36‑28‑10 Revision 2, dated 9 May 2001. After replacement, the repetitive inspections cease.

5. If the age and time‑in‑service of the flapper valve cannot be determined. This is a special case from the original directive. The directive still requires that you replace both flappers of the tip tank in each wing in accordance with Learjet Service Bulletin SB 35/36‑28‑10, dated 6 October 1995, within 50 hours time‑in‑service after 29 February 1996 (but this date has long passed). If you are an operator who has not done this because the records are missing, you must do it as soon as possible. Then you must accomplish the inspection required by Requirement 1 (deterioration inspection) within 600 hours after that replacement. Then you must also comply with Requirement 5 (part‑number identification) within 600 hours after that replacement or 90 days after 27 October 2005, whichever is later. This is a layered requirement.

6. Do not install prohibited parts. From the effective date, no flapper with P/N 2323006‑5 or assembly with P/N 2323006‑6 may be installed. Ensure your parts inventory does not stock these for use on affected aircraft.

7. Document and maintain records. Record all inspections, part numbers found, replacements made, and the basis for any termination of repetitive inspections. This documentation is essential for ongoing airworthiness and for any future sale or re‑registration of the aircraft.

8. Monitor compliance times. The key deadlines are:

   • For Requirement 5: within 600 hours time‑in‑service since the last flapper replacement, or within 90 days after 27 October 2005, whichever occurs later. If you are after this date, you should already have complied. If you acquire an aircraft that has not complied, do so immediately.
   • The original repetitive inspection intervals (600 hours TIS) remain applicable until terminated by the part‑number check.

The overall cost depends on whether a physical inspection is needed and whether replacement parts are required. The parts are aircraft‑specific and may be expensive. The labour involves gaining access to the tip tanks, adhering to the service bulletin procedures, and possibly acquiring specialised tools. Compliance should be planned around scheduled heavy maintenance to minimise downtime.