AD/J4100/6 - Wing Upper Splice Plate

The directive introduces several technical concepts that operators and maintenance engineers must understand for compliance.
Eddy current inspection is a non-destructive testing method used to measure the electrical conductivity of the aluminium wing upper splice plate. The measurement is expressed as a percentage of IACS (International Annealed Copper Standard). A reading below 35.0 percent IACS indicates a higher corrosion risk and triggers further inspection. The threshold is binary: above it, no further action; below it, the borescope step is mandatory.
Borescope inspection is a visual examination of the splice plate’s interior surfaces using an optical probe, intended to detect corrosion pitting, delamination, or other damage that is not visible externally. The directive requires compliance with paragraphs 2.A. and 2.B. of SB J41-57-020 Revision 1 for the borescope procedure.
Wing upper splice plate is a structural component that joins the upper surfaces of the wing sections. The affected part number is 14157126-3. The directive distinguishes between the original part and a replacement part number 14157126-3PF.
Terminating action means that once a replacement splice plate (part number 14157126-3PF) is installed per SB J41-57-021, the operator no longer needs to perform the 12-month repeat borescope inspections required by Requirements 3 and 4. Note 2 of the directive makes this explicit. However, terminating action only applies to the replacement part; a repair that does not replace the original part with the specific PF variant does not terminate the repeat inspection cycle.
Equivalent approved procedure allows operators to use a different inspection method if it has been approved by EASA as equivalent to the prescribed SB. The directive does not define what constitutes equivalence, leaving that determination to EASA or a delegated body.
Compliance times are linked to the effective date of the directive (20 February 2008). The initial eddy current inspection must be completed within three months of that date. The borescope, if triggered, must be done before further flight. Repeat inspections thereafter have a 12-month recurrence interval. For corrosion found within limits, the replacement must occur within three years of discovery.

The AD directly applies to any person or organisation responsible for the continuing airworthiness of BAe Systems (Operations) Jetstream 4100 series aeroplanes. This includes:

• Aircraft operators who hold the aircraft on their Australian air operator’s certificate or who are the registered owner. They bear the ultimate legal obligation to ensure compliance before flight. The AD is effective from 20 February 2008, so any operator whose aircraft was in service on or after that date must have taken action, and new entrants into the Australian register after that date must ensure the aircraft’s compliance records match the directive’s requirements.
• Approved maintenance organisations (AMOs) that perform the any of the inspections, repairs, or replacements. The directive requires that the work be done in accordance with specific service bulletin revision levels or EASA-approved equivalent. An AMO lacking the correct revision or EASA approval cannot legally certify the work.
• Maintenance engineers who carry out the eddy current or borescope inspections must be trained in the specific procedures and have access to the correct SB documents. The directive does not mandate specific certification classes, but the work must be done under a maintenance organisation with the appropriate scope.
• Aircraft importers and brokers who bring Jetstream 4100 aircraft into Australia need to verify that the splice plate history meets the AD’s requirements, including whether earlier SB J41-57-019 was performed and what IACS reading was recorded.
• Lessors and financiers with an interest in the aircraft may need to assess compliance costs and potential grounding events.
• OEM and continuing airworthiness management organisations that hold the type certificate or design data must make the relevant service bulletins available.

The applicability scope is defined by construction number, not by registration mark. The AD covers construction numbers 41004 through 41096, and 41102 through 41104. Importantly, construction numbers 41097 through 41101 (likely a typographical sequence in the source reading “41097 through 41001”) are excluded if they were inspected during production. That means a small sub-fleet is permanently exempt, but only if production inspection records demonstrate compliance. Operators of these excluded aircraft still need to confirm that the production inspection occurred; otherwise they may fall back into scope.

The AD creates a hierarchy of mandatory duties, balanced by a limited set of rights that allow operational flexibility.
Duties:

• The primary duty is to accomplish an eddy current inspection of the wing upper splice plate (part number 14157126-3) within three calendar months after 20 February 2008, unless already accomplished to the required standard (Requirement 1).
• If the eddy current reading is below 35.0 percent IACS, the operator must perform a borescope inspection of the same plate before further flight (Requirement 2). The borescope must follow paragraphs 2.A. and 2.B. of SB J41-57-020 Revision 1 or later EASA-approved revision.
• When no corrosion is found, the operator must re-inspect the plate at intervals not exceeding 12 months using paragraph 2.B. of the same SB (Requirement 3).
• When corrosion is found but is within the limits of Figure 1 of SB J41-57-020 Revision 1, the operator must re-inspect every 12 months and, within three years of discovering the corrosion, replace the splice plate with a new part per SB J41-57-021 Revision 1 (Requirement 4).
• When corrosion exceeds the acceptable limits, the operator must replace or repair the splice plate before further flight, using a repair approved by EASA or the replacement per the SB (Requirement 5).
• The compliance clock runs from the effective date, not from the aircraft’s last inspection, except where the directive says “unless already accomplished.”

Rights:

• The operator may use any EASA-approved later revision of the specified service bulletins, not necessarily the original issue. This allows flexibility if the manufacturer refines the procedures.
• The operator may use an equivalent approved procedure for the eddy current inspection (Requirement 1 includes “equivalent approved procedure”). The equivalent procedure must be approved by EASA; the directive does not allow self-declaration of equivalence.
• The operator has the right to terminate repeat inspections by installing a replacement splice plate part number 14157126-3PF per SB J41-57-021. Once this terminating action is performed, the 12-month repeat borescope inspections of Requirements 3 or 4 are no longer required. Note 2 makes this right explicit.
• The operator may choose to repair a corrosion-damaged plate rather than replace it, provided the repair is approved by EASA. However, repair does not terminate repeat inspections unless the repair also involves installation of the PF part.

The directive imposes no obligation to perform the initial eddy current inspection more than once. If the reading is at or above 35.0 percent IACS, the aircraft is exempt from all further actions under this AD. There is no duty to re-check the conductivity later, even though the background links corrosion susceptibility to conductivity. That creates a static, one-off gate: a plate that passed in 2008 is permanently considered safe even if material properties could degrade over time.

The directive itself does not recite penalty provisions, but it is a legislative instrument made under the Civil Aviation Act 1988 and the Civil Aviation Regulations 1988 (specifically regulation 37 which governs airworthiness directives). Non-compliance is a breach of the Act and Regulations and can attract enforcement action by the Civil Aviation Safety Authority (CASA).
Potential enforcement consequences include:

• Civil penalties under section 20AA of the Civil Aviation Act, which provides for pecuniary penalties for contraventions of the safety regulations. The maximum penalty for a corporation can be significant (hundreds of thousands of dollars per contravention).
• Criminal prosecution under section 20A of the Act for reckless or intentional contravention that endangers the safety of an aircraft.
• Administrative action by CASA, including suspension or cancellation of an air operator’s certificate, a maintenance organisation’s approval, or an individual’s licence.
• Grounding of the aircraft until compliance is demonstrated. The directive itself implies that non-compliance renders the aircraft unairworthy, so it cannot be operated.

Because the AD is issued by a delegate of CASA, it has the same legal force as a regulation. Operators who fail to meet the 3-month initial deadline or who operate an aircraft without completing the borescope before flight risk immediate enforcement. The 12-month repeat inspections are ongoing obligations; each missed interval constitutes a separate contravention.

The directive does not specify a right of appeal, but the general administrative law of Australia would allow a person affected by the AD to seek merits review in the Administrative Appeals Tribunal (AAT) or judicial review in the Federal Court. Historically, challenges to airworthiness directives are rare due to the safety justification and the presumption that CASA’s expert judgment is sound. However, if a directive imposes disproportionate costs without scientific evidence, a challenge could theoretically succeed.

The AD also cross-references EASA approval, which implies that CASA accepts EASA’s regulatory decisions. That creates a dual enforcement layer: if an operator uses an EASA-approved revision but EASA subsequently revokes that approval, CASA may treat the work as non-compliant. Operators should monitor EASA’s status of the referenced bulletins.

This AD does not exist in isolation. It interacts with several other legal instruments and regulatory frameworks.
Civil Aviation Regulations 1988 (CAR) : The AD is issued under CAR 37, which empowers CASA to prescribe mandatory continuing airworthiness requirements. CAR 37 makes it an offence to operate an aircraft that does not comply with an applicable AD. The AD therefore sits within the same regulatory hierarchy as other maintenance and operational requirements in CAR 1988 and the Civil Aviation Safety Regulations 1998 (CASR).
EASA AD 2007-0056 : The directive notes in Note 3 that “EASA AD 2007-0056 refers.” This indicates that the European Aviation Safety Agency issued a parallel AD for the same subject. The Australian AD is likely based on or harmonised with that EASA AD. However, the compliance times and applicability may differ. Operators of aircraft on the Australian register must comply with the Australian AD, not the EASA AD, though using EASA-approved revisions is permissible. For aircraft that are also registered in an EASA member state, the operator must comply with both, and the stricter requirement applies.
Service Bulletins : The directive incorporates by reference three service bulletins: J41-57-019, J41-57-020, and J41-57-021, each at stated Revision 1 or later EASA-approved revision. These SBs are not legislation but are contractual documents produced by the type certificate holder (BAE Systems (Operations) Limited). By being referenced in the AD, the SBs become mandatory legal requirements. However, the SBs themselves may change with revisions. The operator must use the revision that is current at the time of the work, provided EASA has approved it.
Maintenance Regulations under CASR : Part 42 (Continuing Airworthiness) and Part 145 (Approved Maintenance Organisations) of CASR 1998 govern how the work is recorded, who can certify it, and what documentation is required. The AD does not specify the data requirements, but the maintenance release must reflect compliance with the AD. The eddy current reading must be recorded in the aircraft logbook or maintenance record.
Export and Import Regulations : An aircraft imported into Australia must have a Certificate of Airworthiness. CASA will check AD compliance during the import process. Missing AD actions can delay or prevent certification.
Insurance : While not a direct legal interaction, an operator’s liability insurance policy may require compliance with all ADs. Non-compliance could void coverage in the event of an incident.

The directive does not list a formal amendment history of itself, but it explicitly references the revision status of the incorporated service bulletins and contains a background note about a revision to one of those SBs.

• Service Bulletin J41-57-019 : The AD requires compliance with either the original issue or Revision 1 (or later EASA-approved revision). The AD does not state when Revision 1 was issued, but it is presumably later than the original and may have refined the eddy current procedure or scope.
• Service Bulletin J41-57-020 : The AD refers to Revision 1. The background mentions that “Revision 1 of SB J41-57-020 extends applicability to include aircraft construction numbers 41102 through 41104.” This implies that the original issue of SB J41-57-020 did not cover those construction numbers, and the amendment brought them into scope. The AD effective 20 February 2008 captures that expanded scope.
• Service Bulletin J41-57-021 : The AD refers to Revision 1 of this SB for the replacement procedure. No earlier revision is mentioned, so it appears that Revision 1 is the baseline.
• EASA AD 2007-0056 : This foreign AD, referenced in Note 3, presumably has its own amendment history. The Australian AD does not incorporate any amendments to that EASA AD, so changes to EASA AD 2007-0056 do not automatically flow into the Australian requirement.
• The AD itself appears to be a single issue with no subsequent amendments on the face of the source. The text “AD/J4100/6” suggests this is the sixth AD for this aircraft type under that numbering system. No revision letter appears after the AD number.

There is no mention of any amendment to the AD’s compliance times or requirements. The effective date is 20 February 2008, and the compliance times run from that date. Operators who brought aircraft into the fleet after that date must still comply using the original deadlines (e.g., the 3-month initial eddy current inspection would have been calculated from the AD’s effective date, not from the date the aircraft entered the Australian register). This is a potential trap for new entrants.

The source text for this airworthiness directive contains no reference to any litigation. There is no discussion of court challenges, tribunal reviews, or case law involving AD/J4100/6. This absence is common for individual ADs; they are rarely litigated in their own right. The reasons are several. First, ADs are issued on the basis of safety findings that are hard to contest on merits. Second, the cost of challenging an AD often outweighs the cost of compliance. Third, operators prefer to avoid regulatory friction with CASA.
Nonetheless, legal challenges to ADs in Australia are possible. The Administrative Appeals Tribunal (AAT) hears applications for review of decisions under the Civil Aviation Act. An AD itself is not a reviewable decision in the AAT unless it is part of a broader refusal or variation of a certificate. However, a person could seek judicial review in the Federal Court under the Administrative Decisions (Judicial Review) Act 1977 on grounds such as procedural error or jurisdictional error. No such case is known publicly for this specific AD.
The directive’s background says corrosion was “detected during a routine four year structural inspection.” That fact alone is not a finding that would invite challenge. The scientific link between conductivity and corrosion susceptibility appears to have been accepted.
It is worth noting that the AD relies on EASA’s approval of service bulletin revisions. If EASA’s approval were later quashed on appeal in Europe, the legal basis for the Australian AD could be undermined, but that would require litigation in the European courts.
The Australian AD also incorporates strict compliance times: “within 3 months after 20 February 2008” for the initial eddy current inspection. If an operator missed that deadline due to a scheduling error, CASA could prosecute. There is no known case where a Jetstream 4100 operator successfully argued impossibility or impracticality as a defence.
Thus, while there is no recorded litigation history, the AD’s design creates legal risk for non-compliant operators and theoretically could be tested in court if compliance were genuinely impossible.

Several aspects of the directive can trap the unwary operator or maintenance organisation.
Applicability nuance based on prior SB history : The AD applies to aircraft that have not had SB J41-57-019 or equivalent inspection or have had that inspection but the eddy current reading is below 35.0 percent IACS. This means an aircraft that had the SB done but recorded a low reading remains fully in scope. There is no exemption for aircraft that had the SB but with a reading that later dropped (the AD does not mandate a second eddy current check). Conversely, an aircraft that has the SB with a reading above the threshold is exempt. Operators must not assume that past SB compliance automatically clears them; they need to check the actual recorded IACS number.
Construction number exclusions : The note says aircraft construction numbers 41097 through 41001 were inspected during production and do not require additional action. The sequence appears truncated or misprinted; it likely means 41097 through 41101. But the text says “41097 through 41001” which suggests 41097, 41098, 41099, 41100, 41101. There is no construction number 41001 in the earlier range, so this is likely a typo. Operators should check the actual production records for their aircraft.
No repeat eddy current after initial pass : If the initial eddy current reading is 35.0 percent IACS or above, the AD imposes no further checks ever. The background says corrosion susceptibility is linked to material conductivity, which is presumably a fixed property of the metal. But if conductivity can change over time due to fatigue or heat, the AD leaves a gap.
Terminating action only for replacement : Note 2 says installing a replacement splice plate (part number 14157126-3PF) provides terminating action for the repeat inspections of Requirements 3 or 4. It does not say that a repair provides terminating action. So if an operator chooses to repair a corroded plate within acceptable corrosion limits, they must still carry out 12-month borescope inspections indefinitely, until the plate is replaced with the PF part. This can result in ongoing compliance costs far exceeding the one-off replacement cost.
Within three years of discovery : Requirement 4 imposes a 3-year deadline to replace the plate when corrosion is within limits. If corrosion is discovered in a 12-month inspection, the 3-year clock starts ticking from that discovery. Operators must track the discovery date, not just the inspection date.
Before further flight : The borescope in Requirement 2 and the replacement/repair in Requirement 5 must be done before further flight. That means if an aircraft is at a remote location and an eddy current reading below 35% is found, the aircraft is grounded until a borescope is done. This can cause operational disruptions and unscheduled maintenance costs.
Equivalent approved procedure : Requirement 1 allows “equivalent approved procedure” for the eddy current inspection, but does not define who approves it. In practice, CASA or EASA must approve, and obtaining such approval can take time. Operators should not assume that their in-house procedure is equivalent.

Compliance with AD/J4100/6 requires a systematic, documented approach. The following steps are based on the directive as it reads, assuming the aircraft falls within the applicable construction number range and has not been excluded.

Step 1: Determine applicability
Check the aircraft’s construction number against the list: 41004 through 41096, and 41102 through 41104. If the construction number is 41097 through 41101 (assuming the typographical correction), confirm from production records that the wing upper splice plate was inspected during production. If records are unavailable, treat the aircraft as applicable.

Step 2: Review maintenance records
Check whether SB J41-57-019 or an equivalent inspection was ever performed. If it was, locate the eddy current reading recorded at that time. If the reading is at or above 35.0 percent IACS and the aircraft remains unchanged, no further action is required. If the reading is below 35.0 percent, proceed to Step 4. If no previous SB was done, proceed to Step 3.

Step 3: Perform eddy current inspection
Within 3 calendar months of 20 February 2008 (or if the aircraft entered the register later, the operator must comply as soon as possible, but the AD’s compliance time is fixed from the effective date). Use the procedure in SB J41-57-019 original, Revision 1, or later EASA-approved revision, or an EASA-approved equivalent procedure. Record the IACS reading. If reading >=35.0%, no further action is required under this AD. If reading <35.0%, proceed to Step 4.

Step 4: Perform borescope inspection
Before further flight, conduct a borescope inspection per SB J41-57-020 Revision 1 paragraph 2.A. and 2.B. (or later EASA-approved revision). Assess corrosion against the limits in Figure 1 of that SB.

Step 5: Determine follow-on actions

• If no corrosion is found: schedule repeat borescope inspections at intervals not exceeding 12 months, using paragraph 2.B. of SB J41-57-020 Revision 1. Document the recurrence interval.
• If corrosion is within limits: start the 12-month repeat borescope inspections and plan to replace the splice plate with part number 14157126-3PF within 3 years of the corrosion discovery. Retain the discovery date.
• If corrosion exceeds limits: replace the splice plate per SB J41-57-021 Revision 1, or repair using an EASA-approved repair, before further flight.

Step 6: Consider terminating action
If the operator wishes to end the cycle of 12-month borescope inspections, install the replacement part number 14157126-3PF per SB J41-57-021. This terminates Requirements 3 or 4. Ensure the maintenance record notes the terminating action.

Step 7: Maintain records
Keep copies of the eddy current reading, borescope reports, and any replacement part certificates. The maintenance release must reference AD/J4100/6 and the applicable service bulletin revision.

Step 8: Monitor for revisions
Check periodically whether EASA has approved a later revision of the SBs. If a later revision is approved, the operator may use it, but is not required to unless the AD is amended. However, using the latest revision reduces the risk of CASA challenging the adequacy of the procedure.

Step 9: For imported aircraft
If the aircraft entered Australia after February 2008, verify that the initial eddy current inspection was performed within 3 months of the AD’s effective date. If it was not, the aircraft is likely non-compliant and may require a one-time approval from CASA to accept late compliance.

Step 10: Budget
The costs include labour for the eddy current inspection (non-destructive testing specialist), borescope inspection (engineer time), replacement parts (part number 14157126-3PF), and potential grounding if corrosion is discovered at a remote base. Recurrent 12-month inspections add to ongoing maintenance costs. A replacement part eliminates future inspection costs but involves a significant upfront expense.