AD/CL-600/69 Amdt 1 - Horizontal Stabiliser Trim - Uncommanded Movement

The central concept is uncommanded horizontal stabiliser trim movement. The horizontal stabiliser trim adjusts the aircraft’s pitch attitude without moving the elevator. Uncommanded movement means the trim moves without pilot input, which can be hazardous, particularly during takeoff or landing. The AD is triggered by two such incidents.

An airworthiness directive (AD) is a mandatory corrective action issued by CASA under the Civil Aviation Act 1988 to address an unsafe condition. Compliance is compulsory; operating an aircraft that does not comply with an applicable AD renders it unairworthy. This AD is an amendment (Amdt 1) to AD/CL-600/69, meaning it supersedes an earlier version with revised requirements.

The Temporary Revision (TR) to the AFM is a standard method to rapidly insert new operating procedures. TR 604/21-1 dated 3 October 2006 replaces an earlier TR 604/21 dated 1 August 2006. The AFM is an approved document; the TR updates the stabiliser trim runaway procedure. Once the AD is fully complied with (HSTCU replaced), the TR may be removed or superseded by a permanent revision, though the AD does not explicitly require its removal.

Circuit breaker quick identifier collars are physical markers (coloured bands or labels) installed around the STAB CH1 and STAB CH2 HSTCU circuit breakers. They allow flight crew to rapidly locate these breakers in an emergency. The collars are an interim measure; they may be removed after the HSTCU is replaced.

The HSTCU (Horizontal Stabiliser Trim Control Unit) is the electronic control unit governing the stabiliser trim. The AD mandates replacement with part number 601R92301-15 (Vendor P/N 7060-10) or a higher mod number, per Bombardier Alert Service Bulletin A604-27-029. The new unit includes environmental protection on the motherboard to prevent the corrosion and short-circuiting that caused the incidents.

Terminating action means that once the HSTCU is replaced, the interim measures (collars and special pre-flight checks) are no longer required. The AD explicitly permits removal of the collars after the new HSTCU is installed. However, the AFM TR may remain until a permanent revision is issued.

Compliance time is set in two tiers: within 14 days for the AFM revision, collars, and crew awareness; within 12 months for the HSTCU replacement. The effective date is 27 October 2006. Operators must plan accordingly, noting that the 14-day window is tight.

Applicability is limited to Model CL-600-2B16 (CL-604) serial numbers 5301 through 5665. Aircraft outside this range are not affected, which reflects the specific nature of the defect. This narrow scope reduces the compliance burden on the broader fleet but imposes concentrated costs on owners of those serial numbers.

The notes in the AD are not mandatory but recommend that operators reinstate the functional check of the stabiliser trim system on the first flight of the day. This is advisory; however, the AD separately mandates a check under Requirement 3. The note also references TCCA AD CF-2006-21R1, indicating this is a harmonised directive.

The background is factual and explains the root cause and the rationale for each requirement. It attributes the malfunction to manufacturing omissions at the motherboard level, not to operator or maintenance errors. This background may be relevant if an operator needs to explain the AD to crew or insurers.

The primary affected parties are operators of Bombardier CL-600-2B16 (CL-604) aeroplanes with serial numbers 5301 through 5665 inclusive. These operators are typically corporate flight departments, charter companies, private owners, and lessors. The aircraft in this range are business jets commonly used for executive transport and charter. The operator is responsible for ensuring compliance with the AD under the Civil Aviation Act.

Flight crew are directly affected. The AD mandates that on the first flight of each day, crew must review the location of the STAB CH1 and STAB CH2 HSTCU circuit breakers and perform a stabiliser trim system check as per the AFM Normal Procedures. This adds a procedural step to the pre-flight routine. Crew must also be made aware of these requirements; operators can place a copy of the amendment in the AFM to satisfy this, but a briefing or training session is also needed to ensure understanding. For pilots operating multiple sectors, only the first flight of their duty day requires the review, but any change of crew during the day means that new crew must also do the review before their first flight.

Maintenance organisations that hold CASA approval to perform airframe maintenance on the CL-604 will be tasked with installing the circuit breaker collars and replacing the HSTCU. They must have access to Bombardier Alert Service Bulletin A604-27-029 and any later TCCA-approved revisions. They must also obtain the specified parts. The work will require aircraft downtime and coordination with the operator.

CASA itself is affected as the issuing authority; it must administer compliance, potentially through surveillance or audits. The AD was signed by a delegate of CASA, James Coyne. CASA will expect to see evidence of compliance in aircraft maintenance records.

Manufacturers are affected. Bombardier produced the Alert Service Bulletin; the HSTCU vendor (indicated by vendor P/N 7060) supplies the replacement units. The AD mandates a specific part and service bulletin, which creates demand for that supplier’s product. This may incentivise timely production but also creates a dependency that could cause supply constraints if demand outstrips inventory.

Lessors and financiers often include compliance with all applicable ADs as a condition in lease agreements. Non-compliance could be a breach of contract. The AD therefore creates obligations not only to the regulator but also to counterparties in commercial arrangements.

Insurance companies may adjust premiums or terms based on AD compliance. Failure to comply could be used to deny coverage in the event of an incident.

Indirectly, passengers and crew flying in these aircraft benefit from the safety improvement. However, the cost of compliance is ultimately passed on through higher charter rates or operating budgets, which affects consumers.

The AD does not affect operators of other CL-600 variants (CL-600, CL-601, CL-605) or CL-604 aircraft outside serial numbers 5301-5665. This limits the economic impact to a specific subset of the fleet, but for those operators the burden is mandatory and non-negotiable.

The AD imposes several specific duties on the aircraft operator. Under Requirement 1, the operator must amend the AFM by inserting Temporary Revision TR 604/21-1 dated 3 October 2006 (or later approved changes) and remove the previous TR 604/21 dated 1 August 2006. This must be done within 14 days of the effective date. The duty includes ensuring that each copy of the AFM in each affected aircraft is updated and that the old TR is physically removed. The operator also has a duty to ensure the TR is the correct version: only revisions approved by the Chief, Continuing Airworthiness, TCCA satisfy the requirement.

Under Requirement 2, the operator must install circuit breaker quick identifier collars on the HSTCU circuit breakers (STAB CH1 and STAB CH2) in accordance with Bombardier Alert Service Bulletin A604-27-029 dated 28 September 2006, or a later revision approved by TCCA. This duty includes obtaining the correct collars (prescribed in the ASB) and having them installed by an authorised maintainer. Again, within 14 days.

Under Requirement 3, the operator must ensure all flight crew are aware that, on the crew’s first flight of the day, they are required to: (a) review the location of the two specific circuit breakers; and (b) check the stabiliser trim system as detailed in the CL-604 AFM Normal Procedures section “Flight Controls Trim Systems, Before Flight - First Flight of the Day”. The operator may satisfy the awareness component by placing a copy of this amendment in the AFM Normal Procedures section. However, the duty is to ensure crew are aware; mere insertion of a document may not be sufficient if a crew member does not see it. Good practice dictates additional briefing or training.

Under Requirement 4, the operator must install HSTCU P/N 601R92301-15 (Vendor P/N 7060-10) or a higher mod number, in accordance with ASB A604-27-029 (or later approved revision). This must be done within 12 months. This duty includes sourcing the part, arranging for its installation by an authorised maintenance organisation, and documenting the work.

The operator has a right to remove the quick identification collars after the HSTCU replacement is completed, per the AD. This is a permissive right, not a duty. If the operator chooses to remove them, they may do so; if they prefer to leave them, that is also permitted. The AD does not mandate removal.

The operator also has a right to use a later revision of the ASB, provided that revision is approved by TCCA. The operator does not need to use the originally-dated bulletin if a later approved revision exists.

There is no right to delay compliance beyond the specified timelines; the AD is mandatory. The operator does not have a right to alternative means of compliance unless explicitly granted by CASA (not mentioned in this AD). The AD also does not create a duty for the manufacturer to supply parts within a certain time; that is a contractual matter.

Flight crew have a duty to perform the pre-flight checks as described. They also have a right to refuse to operate an aircraft that is not in compliance with applicable ADs, as that would make the aircraft unairworthy. The crew’s awareness duty is imposed on the operator, but crew must act on it.

Maintenance organisations have a duty to perform the work in accordance with the applicable service bulletin and to use parts that meet the specified part numbers. They also have a duty to ensure their work is properly documented.

The AD does not impose any duties on CASA, but CASA has enforcement powers if the duties are not met.

The AD itself does not specify penalty amounts or enforcement procedures. It is issued under the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations 1998 (CASR). Non-compliance with an airworthiness directive is a serious breach. Under the Act, operating an aircraft that is not in compliance with an applicable AD renders the aircraft unairworthy and exposes the operator to enforcement action. CASA can issue infringement notices (on-the-spot fines) for non-compliance; the amount would be set under the regulations. For more serious or repeated breaches, CASA may seek civil penalties through court action, which can be substantial. In extreme cases, criminal penalties may apply if the non-compliance endangers the safety of the aircraft or persons.

Additionally, CASA may suspend or cancel the aircraft’s certificate of airworthiness, or the operator’s air operator certificate (AOC) if they hold one. This would ground the aircraft and prevent revenue generation until compliance is achieved and CASA is satisfied. The AD does not create a grace period; failure to meet the 14-day or 12-month deadlines is a breach immediately upon the expiry of those periods.

Enforcement is typically carried out through surveillance (ramp checks, records audits) or through investigation following an incident. If CASA identifies non-compliance, it may issue a direction to ground the aircraft or a notice of proposed enforcement action. The operator bears the cost of ensuring compliance and any legal costs if challenged.

The AD does not specify record-keeping requirements, but good practice is to document all actions: AFM TR insertion date, collar installation date and part numbers, crew briefing records, and HSTCU replacement details. Failure to maintain such records may itself be a breach of maintenance recording requirements under CASR, and would make it difficult to prove compliance during an audit.

The note in the AD recommending reinstatement of the functional check is not mandatory; failure to follow it is not a breach of the AD. However, if the operator fails to do the mandatory pre-flight check under Requirement 3, that is a breach.

The cross-reference to TCCA AD CF-2006-21R1 does not impose penalties under Canadian law on Australian operators, but it may be relevant if the aircraft operates in Canada or is subject to Canadian regulations. The CASA AD is the binding instrument in Australia.

There is no mention in the source of any previous enforcement action related to this AD. The background indicates the incidents were investigated by Transport Canada and the root cause was a manufacturing issue, not operator non-compliance. The AD is preventive, not punitive.

The cost of non-compliance includes not only potential fines but also the economic consequences of grounding and reputational damage. For a charter operator, even a brief grounding can result in lost revenue and customer dissatisfaction. The AD incentivises timely compliance, as the 14-day window is short and the 12-month window allows planning but carries risk of supply delays.

This AD is a domestic regulatory instrument under the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations 1998. It applies to Australian-registered aircraft. The AD explicitly notes that TCCA AD CF-2006-21R1 refers, indicating that this directive is aligned with the Canadian airworthiness authority’s requirements. Bombardier is a Canadian manufacturer, and Transport Canada is the state of design. The CASA AD effectively adopts or mirrors the Canadian AD, ensuring consistency across jurisdictions. An operator who complies with the CASA AD will likely also satisfy the Canadian AD, subject to any differences in applicability or wording. However, if the aircraft operates in Canada or under a Canadian certificate, the operator must check TCCA requirements directly.

The AD interacts with the aircraft’s type certificate and the original AFM. The AFM is an approved document; the AD overrides it temporarily by mandating insertion of a TR. Once the TR is inserted, the AFM is modified. After the terminating action (HSTCU replacement), the TR may be removed if a permanent AFM revision is issued; otherwise it may remain. The operator must follow the procedures in the TR as part of the AFM.

The AD also interacts with the aircraft’s approved maintenance program. The HSTCU replacement is a one-time mandatory modification; it is not a recurring task. However, the pre-flight check mandated by the AD may need to be incorporated into the operator’s daily procedures, and the note recommends reinstating the check permanently. If the operator already had that check in their procedures, no change is needed; if not, it must be added.

The AD references Bombardier Alert Service Bulletin A604-27-029. That service bulletin is not itself law, but the AD makes compliance with it mandatory. The AD also requires that later revisions of the ASB be approved by the Chief, Continuing Airworthiness, TCCA. This is consistent with CASA’s policy of recognising TCCA approvals under bilateral agreements. If a revision is approved by TCCA but not yet accepted by CASA, operators should verify current status before using it.

The AD does not conflict with other Australian laws such as workplace health and safety or employment law. It may interact with industrial agreements regarding crew duties if adding the pre-flight check extends duty time or changes procedures.

The AD does not create any private rights of action for passengers or third parties. Non-compliance may be used as evidence of negligence in a civil lawsuit if an accident occurs, but the AD itself does not confer a right to sue.

If the aircraft is leased or financed, the lease or loan agreement will typically require compliance with all ADs. Non-compliance could be a default event. Similarly, insurance policies may exclude coverage for accidents resulting from non-compliance.

The AD is specific to Model CL-600-2B16 (CL-604) serial numbers 5301-5665. If an operator has aircraft outside that range, they are not subject to this AD, but other ADs may apply. There is no interaction with those.

The AD does not duplicate or contradict any other CASA AD covering the same issue. It is the sole mandatory requirement for this problem on this aircraft type.

The source identifies this as Amendment 1 to AD/CL-600/69. The original issue of this directive became effective on 6 September 2006. This amendment becomes effective on 27 October 2006. The amendment changes the required AFM Temporary Revision from TR 604/21 dated 1 August 2006 to TR 604/21-1 dated 3 October 2006. The original AD likely required insertion of the earlier TR; this amendment requires removal of that TR and insertion of the new one. The amendment also adds the requirement to install circuit breaker quick identifier collars and provides the terminating action of HSTCU replacement within 12 months. The original AD may have only required the AFM change and crew checks; this amendment expands to include collars and final HSTCU replacement.

The background notes that the original directive became effective 6 September 2006. The amendment was signed on 23 October 2006 by James Coyne, Delegate of CASA, and becomes effective 27 October 2006. The document number is 13/2006 DM. The format of the source indicates this is a consolidated version of the amendment; it does not reproduce the original AD text separately. The AD number remains AD/CL-600/69, with Amdt 1 appended.

The amendment was likely prompted by further investigation into the root cause (missing corrosion protection on the motherboard) and the development of a service bulletin and replacement part. The original AD was likely an interim action; this amendment provides more comprehensive requirements and a final fix. The compliance times reflect this: the interim actions (AFM, collars, crew checks) are due within 14 days (urgent), while the HSTCU replacement has a 12-month window to allow manufacturing and installation.

There is no indication of any earlier amendments or of any subsequent amendments to this directive within the source. The AD references TCCA AD CF-2006-21R1, which may have its own revision history as indicated by the “R1” suffix. The CASA AD is consistent with that revision.

The amendment history demonstrates the regulatory process: initial urgent AD followed by a more comprehensive amendment after engineering solutions are developed. This is typical for airworthiness directives addressing newly discovered unsafe conditions. Operators who complied with the original AD must now take additional steps; they cannot rely on past compliance. Those who had not yet complied with the original AD should comply directly with this amendment.

The effective date of 27 October 2006 is key for calculating compliance times. The 14-day window for Requirements 1-3 expires on 10 November 2006. The 12-month window for Requirement 4 expires on 27 October 2007.

The source text does not name any court cases or litigation related to this airworthiness directive or the incidents that led to it. The background mentions two reports of uncommanded horizontal stabiliser trim motion, but in each case the aircraft landed safely. There is no indication of any personal injury, property damage, or fatal accidents arising from these incidents. It is likely that no litigation resulted from these events, as the aircraft landed without further damage.

There is also no reference to any challenge to the AD itself. Airworthiness directives can occasionally be challenged in court on grounds of procedural fairness or reasonableness, but the source does not suggest any such challenge occurred. Given that the AD is technical and safety-driven, judicial review is rare. The absence of litigation history suggests the directive was accepted by the industry without dispute.

The AD cross-references TCCA AD CF-2006-21R1. That Canadian AD may have its own litigation history, but the source does not mention it. The user must not assume facts outside the source. Accordingly, there is no litigation history to report from this document.

The lack of litigation does not diminish the legal force of the AD. It remains mandatory and enforceable.

Several aspects of this AD can easily trip up operators or maintenance personnel if read quickly. Each is a potential source of inadvertent non-compliance.

First: the AFM TR must be replaced even if previously installed. Requirement 1 states: “If not previously accomplished, amend the AFM … by inserting Temporary Revision (TR) 604/21-1 dated 3 October 2006, or later approved changes to this TR. TR 604/21 dated 1 August 2006, which was installed under the original issue of this Airworthiness Directive, should be removed.” This means any operator who complied with the original AD by inserting TR 604/21 must now remove it and insert the new TR 604/21-1. The 14-day clock applies. Operators might mistakenly think their previous compliance suffices; it does not.

Second: the 14-day compliance period starts from the effective date, not the date of publication or receipt. The effective date is 27 October 2006. Requirements 1, 2, and 3 must be done within 14 days of that date, i.e., by 10 November 2006. Operators must act immediately, including ordering collars and organising AFM updates. If the collars are not in stock, there is no grace period. The AD does not provide for an extension.

Third: the collars are to be installed per the Alert Service Bulletin, not just any collar. The AD says “in accordance with Bombardier Alert Service Bulletin (ASB) A604-27-029 dated 28 September 2006, or later revision approved by the Chief, Continuing Airworthiness, TCCA.” If the operator uses a generic collar not specified in the bulletin, it may not satisfy the requirement. The bulletin likely specifies a particular part number or size.

Fourth: the pre-flight check is required only on the first flight of the day, but that applies to each crew’s first flight, not just the aircraft’s first flight. The AD says “on the flight crew’s first flight of the day”. If a crew changes mid-day (e.g., a new crew takes over for a second leg), that new crew must review circuit breaker locations and perform the check before their first flight, even if the aircraft already flew that day. Operators and crew may misunderstand this and only perform the check once per aircraft per day.

Fifth: the crew awareness requirement can be satisfied by placing a copy of this Amendment in the AFM Normal Procedures section, but that may not be adequate if the crew does not read it. The AD says “This may be accomplished by placing a copy of this Amendment in the AFM ‘Normal Procedures’.” It does not say this is the only method; it is an example. An operator who simply puts a paper copy in the AFM but does not brief the crew risks non-compliance if a crew member does not see it. The operator has a duty to “ensure all flight crew are aware”; the AFM insertion is a means, not a guarantee.

Sixth: the HSTCU replacement must be with P/N 601R92301-15 (Vendor P/N 7060-10) or a higher Mod Number. The AD states “install HSTCU, part number (P/N) 601R92301-15, (Vendor P/N 7060-10) or a higher Mod Number”. The phrase “higher Mod Number” refers to a later modification state of that same part family. An operator cannot substitute a different part number without CASA approval. The AD is explicit.

Seventh: after HSTCU replacement, the collars may be removed, but only if the new HSTCU is the correct version. The AD says: “Following installation of HSTCU Vendor P/N -10 or higher, it is permissible to remove the quick identification circuit breaker collars.” If the operator installs a lower mod number (e.g., Vendor P/N 7060-9), the collars must remain. The AD ties the removal right to the specific part version.

Eighth: the note recommending reinstatement of the functional check is not mandatory, but the pre-flight check in Requirement 3 is mandatory. Confusion could arise if an operator treats the check only as a recommendation. The check in the AFM Normal Procedures section is mandatory under Requirement 3; the note is about reinstating it if it had been removed from the operator’s procedures. The AD does not require the check to be performed after the HSTCU replacement, but the note suggests doing so.

Ninth: the AD applies only to serial numbers 5301 through 5665, but operators must verify serial numbers carefully. A misidentification could lead to missing compliance on an affected aircraft or unnecessarily doing work on an unaffected one. The serial range is narrow, but the consequences of getting it wrong include regulatory action if an affected aircraft is not complied with.

Tenth: the AD requires use of a service bulletin revision approved by the Chief, Continuing Airworthiness, TCCA. If Bombardier issues a later revision, it cannot be used unless TCCA has approved it. Operators must check the approval status before using a revision other than the original 28 September 2006 version.

Compliance with AD/CL-600/69 Amdt 1 requires a structured approach. The operator of each affected aircraft (CL-604, s/n 5301-5665) should take the following steps in order of priority and time sensitivity.

Step 1: Identify affected aircraft. Verify that the aircraft serial number falls within 5301 to 5665 inclusive. This can be done from aircraft registration documents, airframe logbooks, or the manufacturer’s delivery records. An operator with multiple aircraft should list each and check its applicability.

Step 2: Obtain required documents and parts immediately. Within 14 days (by 10 November 2006), the operator needs to have on hand: Bombardier Alert Service Bulletin A604-27-029 (dated 28 September 2006 or later TCCA-approved revision); Temporary Revision 604/21-1 (dated 3 October 2006 or later approved changes); circuit breaker quick identifier collars as specified in the ASB; and a copy of this AD amendment (to be placed in the AFM). Order the collars as soon as possible; if they are not readily available, contact Bombardier or an approved distributor expedite delivery. Also order the HSTCU part (Requirement 4) early to avoid supply delays within the 12-month window.

Step 3: Amend the AFM. Within 14 days, for each affected aircraft, physically insert TR 604/21-1 into the AFM. Remove the previous TR 604/21 dated 1 August 2006, which was required by the original AD, if it is present. Ensure that all copies of the AFM in the aircraft (cockpit, maintenance, operator’s offices) are updated. Record the amendment in the AFM revision log. The TR should be placed in the correct section; the AD says to insert it in the AFM “Normal Procedures” section, which is consistent with the TR’s content.

Step 4: Install circuit breaker collars. Within 14 days, have an authorised maintenance organisation install quick identifier collars on the STAB CH1 HSTCU and STAB CH2 HSTCU circuit breakers in the flight deck. Follow the instructions in ASB A604-27-029 exactly. The collars are likely coloured rings or tags that identify the breakers as HSTCU-related. After installation, document the work in the aircraft maintenance log or equivalent record, noting the AD compliance and the part numbers used.

Step 5: Establish crew awareness and pre-flight procedures. Within 14 days, ensure that all flight crew who operate the aircraft are aware of the two requirements for the first flight of each day: (a) review the location of the STAB CH1 and STAB CH2 circuit breakers; and (b) perform the stabiliser trim system check as detailed in the CL-604 AFM Normal Procedures section titled “Flight Controls Trim Systems, Before Flight - First Flight of the Day”. The AD says this awareness can be accomplished by placing a copy of this amendment in the AFM Normal Procedures section. Do that for each AFM copy. Additionally, brief all current crew in writing or at a meeting. For new crew members, include the requirement in initial and recurrent training. Consider creating a placard or checklist item. Maintain a record of crew briefings.

Step 6: Monitor and enforce daily compliance. Establish a system to ensure that crew actually perform the pre-flight check on the first flight of each day. This may involve modifying the operator’s pre-flight checklist or adding a sign-off. Crew should also review the circuit breaker locations. The check is mandatory until the HSTCU is replaced and could be kept as a recommended practice thereafter.

Step 7: Schedule HSTCU replacement. Within 12 months of the effective date (by 27 October 2007), install HSTCU P/N 601R92301-15 (Vendor P/N 7060-10) or a higher mod number, in accordance with ASB A604-27-029 (or later TCCA-approved revision). Coordinate with a maintenance organisation that has the capability and approval to perform the work. Ensure that the HSTCU is the correct version. The work will require aircraft downtime; schedule it well in advance, possibly during a planned heavy maintenance check. After installation, perform any required functional tests per the ASB. Update the aircraft records with part numbers, serial numbers, and compliance reference.

Step 8: After HSTCU replacement, optionally remove collars. The AD permits removal of the quick identifier collars. Decide whether to remove them or leave them. If they are removed, they may be discarded or stored as spares. Document the removal if desired. No further action is required for collars.

Step 9: Review AFM TR status. The AD does not require removal of the AFM TR after HSTCU replacement. However, the TR may become obsolete. Contact Bombardier or CASA for advice on whether a permanent AFM revision has been issued that supersedes the TR. If not, the TR may remain indefinitely. The note recommends reinstating the functional check; that check may already be in the TR or the existing AFM. Operators should decide to incorporate the check permanently.

Step 10: Maintain ongoing compliance records. Keep a file for each affected aircraft containing: copy of the AD; evidence of AFM TR insertion; collar installation record; crew training records; HSTCU replacement record; and any correspondence with CASA or Bombardier. This documentation demonstrates compliance during CASA audits or insurance inquiries.

Cost considerations. The direct costs include parts (collars, HSTCU), labour (installation, AFM revision), and crew training. Indirect costs include aircraft downtime for HSTCU replacement and potential lost revenue. Operators should budget for these. The 14-day interim requirements may require overtime or expedited shipping, increasing costs. The 12-month HSTCU replacement allows for cost-effective scheduling but should not be deferred until the deadline; supply chain delays are a real risk.

Alternative means of compliance. The AD does not explicitly provide for alternative means or deviations. If an operator cannot meet the timelines or requires a different part or procedure, they must contact CASA’s airworthiness division to request an exemption or alternate method. This is not guaranteed and likely to be rare.

By following these steps, operators can achieve full compliance and avoid enforcement action. The key is to treat the 14-day window as urgent and to start the HSTCU procurement process immediately after the effective date.