AD/DHC-8/101 Amdt 1 - Fire Bottle Electrical Connectors

Airworthiness Directive (AD) - A legally enforceable notice issued by CASA under Australian aviation law (principally the Civil Aviation Safety Regulations). An AD mandates inspections, modifications or operational restrictions to correct an unsafe condition in an aircraft type. Failure to comply makes the aircraft unairworthy and breaches the law. This AD is numbered AD/DHC-8/101 Amdt 1 and applies only to specified models of the Bombardier DHC-8 series.

Fire bottle - A pressurised container of fire extinguishing agent (typically halon or a replacement) installed in aircraft compartments. The aircraft covered have fire bottles in the forward and aft baggage compartments, in the APU compartment, and in each engine nacelle. The electrical connector on the fire bottle is what triggers the discharge when the fire detection system signals a fire.

Cross‑connection - A condition where the electrical connector from one fire bottle is mistakenly plugged into the receptacle intended for a fire bottle in a different location. If the connectors are crossed, activating the fire suppression for, say, the forward baggage compartment might discharge the aft bottle or none at all, making it impossible to control a fire in the affected area. The background notes three reports of this exact problem.

Lanyard, mount and clamp modification - The physical installation of hardware that prevents the fire bottle connectors from being inadvertently swapped. This is a design change, not merely a procedural check. It involves incorporating Modsum 4-109941 using instructions in Bombardier Service Bulletin 84-26-07 Revision A. The modification is intended to make future misconnection physically impossible.

Service Bulletin (SB) and Alert Service Bulletin (ASB) - Instructions issued by the aircraft manufacturer (Bombardier) for inspections or modifications. The ASB (A84-26-06, dated 12 May 2005) provides the inspection and rectification steps. The SB (84-26-07, Revision A, dated 21 February 2006) provides the modification instructions. Operators must use the exact revision approved by the Chief of Continuing Airworthiness at Transport Canada, unless a later revision is also approved.

Modsum - Bombardier’s modification summary designation. Modsum 4-109941 is the specific engineering change for the lanyard, mount and clamp installation.

Compliance time - The period within which the AD action must be completed. For the inspection it is a fixed calendar time (14 days after the original effective date). For the modification it is a flight-hours threshold (5000 time in service after 3 August 2006). The distinction matters because the inspection deadline has already passed for aircraft in service at the original date, whereas the modification deadline is a future counted from the amendment date.

Effective date - The date on which the AD becomes legally binding. This amendment becomes effective on 3 August 2006. The original AD effective date was 7 July 2005.

Before further flight - A phrase meaning the aircraft may not be flown again until the specified action is taken. Requirement 2 uses this strict ground‑until‑complied standard for correcting deficiencies found during the inspection.

Transport Canada AD CF-2005-14R1 - The Canadian equivalent directive to which this Australian AD refers. Its inclusion signals that the unsafe condition was originally identified by Transport Canada and that the Australian requirement is harmonised with the Canadian action. Operators importing aircraft registered in Canada will need to ensure compliance with both.

Delegate of CASA - The person signing the directive (James Coyne) is a CASA official authorised to issue ADs under delegation from the Director of Aviation Safety.

Basic concept of cross‑connection risk - The AD is built on the premise that incorrectly wiring a fire bottle renders the fire suppression system ineffective. The original AD relied on inspecting each installation. This amendment adds a physical barrier to prevent future human error, reflecting a move toward fail‑safe design rather than reliance on procedural compliance.

The primary duty-holders are the registered operators and owners of the specified aeroplanes on the Australian civil aircraft register. The AD applies to Bombardier DHC-8-400, DHC-8-401 and DHC-8-402 models with serial numbers 4001 through 4107 inclusive (for requirement 3) and, for requirements 1 and 2, serial numbers 4001 through 4105 inclusive. Any person or company operating such an aircraft in Australia must ensure compliance within the stated times. This includes airline operators, charter companies, aircraft lessors, private owners and any entity that has operational control of the aircraft. The AD also directly affects maintenance organisations: approved maintenance providers (typically CASR Part 145 organisations) and licensed aircraft maintenance engineers must carry out the required inspection and modification work in accordance with the specified Bombardier service information. The manufacturer, Bombardier (formerly Boeing Canada/De Havilland), is affected indirectly because it must continue to produce and update the service bulletins and parts (lanyards, clamps, mounts) required for the modification. Bombardier’s role is limited to providing the approved maintenance data. CASA is affected as the issuer and enforcer, but other regulators (notably Transport Canada) are implicated because the Australian AD references the Canadian AD and relies on Bombardier’s instructions approved by Transport Canada’s Chief of Continuing Airworthiness. Passengers and crew are not directly responsible, but they are the ultimate beneficiaries of the airworthiness change. Suppliers of parts for the Modsum 4-109941 modification may see increased demand. Insurers of affected aircraft will take into account whether the operator has complied with the AD when assessing risk and coverage. For lessors of aircraft, the AD imposes obligations that may affect lease terms and return conditions. Any person acquiring an affected aircraft after the effective date should verify that the original inspection requirement (14 days after 7 July 2005) was met at the time the aircraft was placed on the register, or take steps to comply before further flight. The amendment also affects only a relatively small population of aircraft: serial numbers 4001 to 4107 covers perhaps 107 airframes. Not all of those will be registered in Australia. Thus the immediate burden falls on a narrow cohort of operators. The compliance costs (parts, labour, aircraft downtime for the 5000‑hour modification) are concentrated, while the safety benefit (reduced fire risk) is diffuse across all passengers and crew who fly on those aircraft. There is also an effect on engineering organisations: they must ensure their technicians are trained on the new instructions, and their maintenance data libraries are updated with the latest revisions of the ASB and SB. Finally, any foreign operator flying an affected DHC-8 into Australian airspace may be required to show compliance under Australian regulations, so the AD indirectly touches transient operators.

Duty to inspect (requirement 1) - For aircraft serial numbers 4001 through 4105, the operator must ensure that an inspection of the electrical connectors on the forward and aft baggage compartment, APU and engine nacelle fire bottles is carried out. The inspection must be performed in accordance with the Accomplishment Instructions of Bombardier Alert Service Bulletin A84-26-06 dated 12 May 2005 (or later revisions approved by the Chief of Continuing Airworthiness, Transport Canada). The compliance time is within 14 days after the effective date of the original issue of this directive (that is, by 21 July 2005). Because that date has passed, any aircraft that was in service at that time should already have been inspected. For aircraft entering service later, the operator must interpret how the fixed date applies; practically, CASA would expect the inspection to be done before the aircraft first enters service unless an alternative means of compliance is granted.

Duty to correct deficiencies (requirement 2) - If the inspection reveals any deficiencies (such as crossed connectors), the operator must correct them before further flight. The rectification must follow the same ASB instructions. The duty is immediate and does not allow a grace period for parts procurement.

Duty to install or modify lanyards, mounts and clamps (requirement 3) - For aircraft serial numbers 4001 through 4107 inclusive, the operator must incorporate Modsum 4-109941 into the fire extinguishing systems. This involves installing lanyards, mounts and clamps as per Bombardier Service Bulletin 84-26-07 Revision A (21 February 2006) or later revisions approved by Transport Canada’s Chief of Continuing Airworthiness. The compliance time is within 5000 hours time in service after the effective date of this amendment (3 August 2006). The duty can be discharged by showing previous incorporation of Modsum 4-109941 using the original SB 84-26-07 (15 June 2005) before the effective date of this amendment.

Right to use later revisions - For both the inspection and the modification, operators may use later revisions of the respective Bombardier documents, provided those revisions are approved by the Chief of Continuing Airworthiness at Transport Canada. This right gives operators flexibility to adopt improved instructions without needing a separate AD amendment, but it also imposes a monitoring duty to check that any later revision has indeed received that approval.

Right to rely on prior compliance - The AD explicitly accepts prior incorporation of Modsum 4-109941 using the original SB 84-26-07 issue (15 June 2005). Thus operators who acted proactively before the amendment do not need to redo the work. This preserves the investment of earlier compliance.

Obligation to update maintenance manuals - Note 1 states that the Bombardier Aircraft Maintenance Manual PSM 1-84-2 has been amended to clarify connection instructions through Temporary Revisions 26-017 through 26-027. Operators and maintenance organisations must ensure their copies of these manuals are current, as the AD effectively makes those revisions part of the compliance data.

Right to apply for alternative means of compliance? - The AD text does not explicitly mention alternative means of compliance (AMOC). Under Australian law, operators can generally request an AMOC from CASA, but the AD does not set out that pathway. Operators who cannot meet the exact terms (e.g., if parts are unavailable) should seek written approval from CASA before deviating.

Duty to keep records - The AD does not directly mention recordkeeping, but under CASR Part 42 (continuing airworthiness) and Part 145 (maintenance organisations), compliance with ADs must be recorded in the aircraft maintenance records. Operators must retain evidence of inspection results, defects corrected, and modification accomplished.

No right to disregard because of age of original compliance time - Even though the original 14-day inspection period expired long ago, new operators of older serial number aircraft must ensure it was done. The AD does not provide a fresh compliance time for that requirement. That is a gap that operators must resolve.

The source document does not list specific penalty amounts or enforcement mechanisms, but Australian airworthiness directives derive their legal force from the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations 1998 (principally CASR Part 39). Contravening an AD is a breach of regulation. Under the Act, penalties for operating an aircraft that does not comply with an applicable AD include significant financial penalties (currently up to several thousand penalty units, each penalty unit being $313 as at 2025, but amounts vary and are updated yearly, and the AD is from 2006 so historical amounts differ) and potentially imprisonment in severe cases involving reckless endangerment. More practically, CASA’s enforcement tools include: issuing a direction to ground the aircraft (an airworthiness direction); suspending or revoking the aircraft’s certificate of airworthiness; imposing enforceable undertakings; or prosecuting the operator, owner or responsible maintenance organisation. For minor or inadvertent non‑compliance, CASA may issue a warning letter or a civil penalty notice. For deliberate or repeated non‑compliance, criminal prosecution is possible. The AD’s use of the phrase “before further flight” in requirement 2 indicates that any defect discovered during the inspection must be corrected before the aircraft may be flown again. Operating with a known uncorrected defect would be treated as a serious breach. The AD does not allow any grace period for the inspection requirement (the 14‑day period had already passed by the time the amendment was issued). Enforcement also extends to maintenance organisations: if a Part 145 organisation signs off the aircraft as airworthy without ensuring the AD is complied with, that organisation faces regulatory action and potential loss of approval. Additionally, the AD references Transport Canada AD CF-2005-14R1. While the Australian AD is the enforceable instrument in Australia, an operator flying to Canada would also need to be compliant with the Canadian AD, and non‑compliance could result in grounding by Canadian authorities. The compliance requirements are mandatory, and the AD does not offer any exemption or waiver within its text. However, the practical burden is eased by the acceptance of previous incorporation of the modification. Enforcement risk is greatest for operators who ignore the 5000‑hour time‑in‑service requirement, which is a future specified limit. Operators should note that the 5000 hours is counted from the effective date of this amendment (3 August 2006). An aircraft that accumulates 5000 hours after that date must have the modification done before exceeding that figure. Overdue enforcement could include grounding the aircraft until compliance is achieved, plus possible fines for any flights operated after the deadline. Because this AD is a single‑amendment directive, the enforcement history (if any) is not detailed. CASA does not publish a list of enforcement actions specific to each AD. In summary, the consequences of non‑compliance are regulatory action that can halt operations and impose financial costs far exceeding the cost of the modification itself.

This AD sits within the broader framework of Australian aviation law, specifically the system of airworthiness directives established under the Civil Aviation Safety Regulations 1998. While the source text does not cite a specific regulation, ADs in Australia are typically made under CASR Part 39, which gives CASA the power to issue mandatory directives to correct unsafe conditions. This AD also interacts with maintenance regulations: CASR Part 42 (Continuing Airworthiness) requires that operators maintain their aircraft in an airworthy condition, which includes complying with all applicable ADs. CASR Part 145 (Maintenance Organisations) dictates who may perform the inspection and modification; only an approved Part 145 organisation or a licensed aircraft maintenance engineer with appropriate ratings can carry out the work and certify it. The AD also interacts with the aircraft’s type certificate (TC) and type certificate data sheet (TCDS). The DHC‑8 series is type‑certificated by Transport Canada and the FAA; the Australian acceptance of that TC is under Part 21 of CASR. The AD effectively imposes additional design standards to that TC. The reference to Transport Canada AD CF-2005-14R1 creates a cross‑border regulatory link. If that Canadian AD is amended, the Australian AD may need to be amended as well, or operators may rely on the note allowing later service bulletin revisions approved by Transport Canada. This creates a dependency on a foreign regulator’s approval process. The AD also references the Bombardier Aircraft Maintenance Manual (PSM 1-84-2) and its temporary revisions. Those temporary revisions become part of the approved data for maintenance. Under CASR Part 145, the maintenance organisation must use the current approved data; therefore, those temporary revisions must be incorporated into the operator’s maintenance management system. The AD does not expressly incorporate CASR Part 21 (product certification), but the modification (Modsum 4-109941) is a design change that would normally require approval by the design approval holder (Bombardier) and be accepted by the state of design (Canada). The AD validates that modification for affected serial numbers, bypassing any individual supplemental type certificate process. For operators leasing aircraft to or from other countries, the AD may interact with the International Civil Aviation Organization (ICAO) obligations for airworthiness. ICAO Annex 8 requires that aircraft be maintained in accordance with the state of design’s continuing airworthiness requirements; the AD aligns Australia’s requirements with those of Canada (the state of design). There is no conflict with other Australian ADs for the DHC‑8 mentioned in the source, but operators must be aware that multiple ADs may apply to the same aircraft. This AD updates the earlier AD/DHC‑8/101, so the earlier version is superseded to the extent of the amendment. No reference to other Australian legislation such as the Competition and Consumer Act or workplace health and safety law is made, but performing the modification may require compliance with safe work practices (e.g., handling halon). That is not a direct legal interaction but a practical one. Finally, the AD’s Note 2 simply says “Transport Canada AD CF-2005-14R1 refers.” This is ambiguous: it could mean the Canadian AD is a reference document or that the Australian AD adopts it. The more conservative view is that the Australian AD stands alone, but compliance with the Canadian AD may be necessary for operations in Canada or for maintaining dual registration. The interaction is an example of regulatory harmonisation without full legal integration.

The source document is AD/DHC-8/101 Amdt 1, meaning it is the first amendment to an original directive. The original AD/DHC-8/101 became effective on 7 July 2005. That original directive contained requirements 1 and 2 - the inspection of fire bottle electrical connectors and correction of deficiencies - and applied to serial numbers 4001 through 4105. This amendment adds requirement 3, which mandates installation or modification of lanyards, mounts and clamps. It also expands the applicability of that new requirement to include serial numbers 4106 and 4107, i.e., serial numbers 4001 through 4107. The amendment does not alter the compliance times for requirements 1 and 2; the inspection still must have been done within 14 days after the original effective date, and corrections before further flight. The amendment also clarifies that Bombardier Service Bulletin 84-26-07 Revision A (21 February 2006) provides the approved instructions for the modification, but notes that prior incorporation using the original issue of SB 84-26-07 (15 June 2005) is acceptable if done before the amendment’s effective date (3 August 2006). The original S/N scope for requirement 1 is left unchanged, so there is a discrepancy: requirement 1 still applies only to serial numbers 4001-4105, while requirement 3 applies to 4001-4107. The amendment does not explain why serial numbers 4106 and 4107 were added. It may reflect that those aircraft were delivered later and already had the lanyard modification line-fitted, or that the investigation discovered the unsafe condition also applied to them. The background section notes that the original directive became effective on 7 July 2005, and the amendment is based on three reports of crossed connectors. It also states that the original directive already required inspection and rectification. The amendment now requires the design change (lanyards) to prevent future misconnection. This suggests a learning process: the initial approach was detection and correction, and after experience, a more robust preventive fix was mandated. Transport Canada AD CF-2005-14R1 is referenced; that Canadian AD likely underwent a similar amendment. The source does not provide any subsequent amendments (Amdt 2, etc.), so the history ends at this point. No information about why the amendment was required beyond the three reports is given. The original AD was issued on 7 July 2005; this amendment was signed on 21 June 2006 and became effective on 3 August 2006, so the amendment process took about 13 months. The compliance timeline for the new requirement (5000 hours after effective date) likely accounted for the need to design the modification and produce parts. Operators should be aware that the original compliance date for the inspection (14 days after 7 July 2005) may have passed for many aircraft, and new operators must verify whether that inspection was done. The amendment does not re-open that compliance time.

The source text for this AD contains no information about any litigation. There is no reference to court cases, tribunal decisions, or administrative appeals related to AD/DHC-8/101 or its amendment. This does not mean that no litigation ever occurred concerning this directive or its subject matter, but the document itself provides no such details. In the broader context, airworthiness directives are quasi‑regulatory instruments that can be challenged in the Administrative Appeals Tribunal (AAT) or via judicial review in the Federal Court. Grounds might include that CASA exceeded its power, that the process was procedurally unfair, or that the directive is unreasonable. However, given the specific technical nature of this AD and its narrow applicability, litigation is unlikely unless an operator faced disproportionate costs and could argue that alternative means of compliance were available. The AD does cite “three reports of crossed connection” as the basis, suggesting a demonstrated safety risk, which would be a strong justification in any review. The reference to “Transport Canada AD CF-2005-14R1” indicates that the same requirement has been adopted in Canada, so any legal challenges would likely have occurred first in Canada. There is no mention of a US FAA AD, which might have allowed comparisons. Given that this is a 2006 instrument, the time for appeal has long passed. Operators would now be expected to have complied. The absence of litigation in the source might indicate that operators accepted the need, or that any disputes were resolved informally. It would be speculative to assert otherwise. Therefore, the safe statement is that the source contains no litigation history. Analysts should note that this does not foreclose the possibility of private litigation (e.g., if a fire occurred due to non-compliance and the AD was used as evidence of the standard of care). In a tort action, failure to comply with an AD is likely to be strong evidence of negligence. But again, the source does not discuss that.

1. Ambiguous compliance time for requirement 1 for newly registered aircraft. The AD states that requirement 1 compliance “remains unchanged as ‘Within 14 days after the effective date of the original issue of this Directive’.” If an aircraft first enters service on the Australian register after that date (e.g., in 2007), a literal reading would require compliance within 14 days of 7 July 2005, which is impossible. The AD does not provide a fresh compliance trigger. Operators in that situation should obtain a specific direction from CASA regarding an alternative deadline. The risk is that an operator might think the requirement is no longer applicable, but CASA could argue the inspection must be done before flight. The safest approach is to treat the requirement as needing to be done once, and if the aircraft has not been inspected, to do it before further flight.

2. Serial number mismatch between requirements. Requirement 1 applies only to S/N 4001-4105; requirement 3 applies to S/N 4001-4107. So aircraft with S/N 4106 or 4107 must have the lanyard modification, but were never subject to the original inspection. Do those aircraft need the inspection before modification? The AD is silent. The modification (lanyards) is intended to prevent cross-connection, so perhaps inspection is unnecessary, but the AD does not say that. Operators of those two serial numbers should request clarification from CASA.

3. Approval of later revisions. The AD allows use of later revisions of the ASB and SB “approved by the Chief, Continuing Airworthiness, Transport Canada.” If Bombardier issues a revision that Transport Canada has not yet approved, using it could constitute non-compliance. Operators must verify the approval status. Relying solely on the revision number is insufficient.

4. ”Before further flight” for requirement 2 is harsh. If a deficiency is found during inspection, the aircraft may not fly until corrected. This could cause serious operational disruption if parts are not immediately available. The AD does not offer any dispensation for ferrying to a maintenance base. Emergency procedures under CASR Part 39 may allow a permit to fly, but that is not mentioned. Operators should pre‑position parts or arrange contingency.

5. Note 1 amends the maintenance manual. The temporary revisions to the Bombardier Aircraft Maintenance Manual PSM 1-84-2 (TR 26-017 through 26-027) are incorporated by reference. If an operator’s maintenance library is not updated with these TRs, the maintenance personnel may use outdated connection instructions, risking non‑compliance. The AD does not give a deadline for the manual update, but it is implied by the requirement to use the ASB.

6. Previous incorporation using original SB issue. The AD states that “Previous incorporation of Modsum 4-109941 before the effective date of this Amendment, in accordance with the Accomplishment Instructions in the original issue of Bombardier Service Bulletin 84-26-07, dated 15 June 2005, is acceptable.” This is a grace. But what if the modification was done using a different method or a different Modsum? That would not be acceptable. Also, if the modification was done after the effective date using the original SB issue (not Revision A), that is not acceptable unless the revision had been approved as a later revision. So timing and document version matter.

7. Interpretation of “5000 hours time in service after the effective date of this Amendment”. This means the modification must be completed before the aircraft exceeds 5000 hours of operation counting from 3 August 2006. If an aircraft has, for example, 10,000 hours total time on 3 August 2006, the operator has 5000 hours from that date, i.e., must comply by the time the aircraft reaches 15,000 hours total time. Operators must compute correctly and not mistakenly think it is 5000 hours from delivery.

8. No mention of alternative means of compliance. The AD does not include a standard AMOC paragraph. Some directives explicitly say “alternative means of compliance may be used if approved by CASA.” This one does not. An operator needing to deviate should nevertheless apply to CASA, but the AD’s silence may add uncertainty about whether CASA will grant it.

9. Cross‑reference to Transport Canada AD. Note 2 says “Transport Canada AD CF-2005-14R1 refers.” It does not state that compliance with the Canadian AD is equivalent. An operator that complies with the Canadian AD but not the Australian requirements (if they differ) may be non‑compliant in Australia. The note is purely informational.

10. Old effective date for the inspection. The 14‑day period from 7 July 2005 has long passed. Any operator acquiring an affected aircraft today must verify records. If records are missing, the operator should assume the inspection was done and then do the modification, but that assumption could be wrong. A prudent operator would do the inspection again or obtain a clear history.

Operators of affected DHC-8-400, 401, 402 series aeroplanes (serial numbers 4001-4107 for requirement 3; 4001-4105 for requirement 1) must take the following steps, in order. First, identify the aircraft by model and serial number. If the aircraft is within the serial number ranges, proceed. Second, for serial numbers 4001-4105, verify whether the inspection of fire bottle electrical connectors (forward and aft baggage, APU, engine nacelle) was performed in accordance with Bombardier Alert Service Bulletin A84-26-06 (12 May 2005) or an approved later revision. The compliance deadline was 14 days after 7 July 2005. For aircraft that entered service later, the operator should ensure the inspection is done as soon as practical and before further flight if it has never been done. Third, if the inspection reveals any deficiency (crossed connection, damaged connector, etc.), correct it before the next flight using the same ASB’s accomplishment instructions. Fourth, for serial numbers 4001-4107, ensure the lanyard, mount and clamp modification (Modsum 4-109941) is accomplished in accordance with Bombardier Service Bulletin 84-26-07 Revision A (21 February 2006) or a later revision approved by Transport Canada’s Chief of Continuing Airworthiness. This must be completed within 5000 hours time in service after 3 August 2006. Fifth, if the modification was already performed before 3 August 2006 using the original SB 84-26-07 (15 June 2005), that is acceptable and no further work is needed for that requirement. Sixth, update the aircraft maintenance records with proof of compliance for each element: the inspection results (and correction if needed), the modification, and the serial numbers of any parts replaced. Keep copies of the service bulletin revision used and evidence of approval for any later revision. Seventh, ensure that the Bombardier Aircraft Maintenance Manual PSM 1-84-2 is updated to include Temporary Revisions 26-017 through 26-027, as referenced in Note 1. Eighth, operators should contact Bombardier or its approved parts suppliers to obtain the necessary lanyard, mount and clamp kits well before the aircraft reaches the 5000-hour threshold to avoid grounding. Ninth, maintain an ongoing awareness of any later revisions to the ASB or SB that are approved by Transport Canada; if a later revision is published, operators may use it, but they should update their instructions and records accordingly. Tenth, if the aircraft is leased, coordinate with the lessor to ensure the modification is covered under the lease and that the costs are allocated appropriately. Eleventh, for any questions or if an alternative means of compliance is needed, contact CASA’s continuing airworthiness office and seek written approval. Twelfth, consider conducting a risk assessment: the AD addresses a fire bottle misconnection risk that could lead to loss of fire suppression capability. Operators may wish to verify that all fire bottle connectors are correctly labelled and that maintenance personnel are trained on the correct procedure, beyond just the AD requirements. Finally, schedule the modification during a heavy maintenance check to minimise downtime. Because the compliance window is 5000 hours, which likely spans several years, operators should plan well in advance. Record the date of the effective compliance in the aircraft’s continuing airworthiness record system. For operators with multiple affected aircraft, track each aircraft’s progress toward the 5000-hour limit. Non-compliance can result in grounding and enforcement action, so treating this as a critical maintenance event is essential. The AD does not specify a recurrent inspection, so once the modification is done, no further action is required unless a future AD supersedes this one. However, any subsequent AD amendment may alter requirements. Operators should monitor CASA’s AD listings and Bombardier service information for changes.