AD/DHC-8/139 - Spoiler Cable Disconnect Caution Light

The directive is built around a small set of technical and procedural concepts stated in the source material. First, the safety deficiency: the spoiler fuselage cable disconnect sensing system as delivered can produce different cockpit caution-light indications depending on airspeed, specifically only showing ROLL SPLR INBD HYD above 165 knots and both ROLL SPLR INBD HYD and ROLL SPLR OUTBD HYD below 165 knots (Background). That inconsistency is the design symptom targeted by the AD because it can degrade pilot situational awareness and increase workload during approach and landing if a cable disconnect occurs.

Second, the engineering corrective actions are identified as two separate "Modsums" that rework the sensing circuit. Each Modsum corresponds to a particular batch of serial numbers: Modsum 4-110066 for earlier S/Ns (4003, 4004, 4006, 4008-4094) and Modsum 4-126356 for later S/Ns (4095-4129). The AD specifies which Bombardier Service Bulletin contains the approved installation instructions for each Modsum: SB84-27-33 for Modsum 4-110066 (original issue 6 June 2007) and SB84-27-28, Revision B (25 September 2007) for Modsum 4-126356 (Requirement a and b). Note 1 expressly allows installation of Modsum 4-126356 in accordance with earlier SB84-27-28 issuances (original 2 October 2006 or Revision A dated 30 April 2007) as acceptable for compliance.

Third, regulatory interplay: while CASA is the issuing authority (document signed by a CASA delegate), the AD requires use of SB revisions "approved by the Chief, Continuing Airworthiness, Transport Canada," and expressly refers to Transport Canada AD CF-2008-13 (Note 2; Requirement). Therefore compliance hinges not only on following Bombardier SB instructions but on those SB revisions being approved by the specified Canadian authority. The AD therefore uses foreign authority approvals as the basis for acceptable method material.

Fourth, timing and scope: the AD becomes effective on a stated date (10 April 2008) and sets a compliance period measured in aircraft time in service, namely within 6000 hours after that effective date (Compliance). The mechanism thus targets operators’ maintenance scheduling and utilisation rather than calendar deadlines.

Finally, production retrofit status: the AD notes that Modsum 4-126356 was installed in production on S/N 4130 and later, so aircraft with S/N 4130 onward already contain the corrective work and are outside the AD’s applicability (Background).

The AD identifies several distinct groups directly or indirectly affected, each following from the AD text. Primary affected parties are operators and owners of Bombardier (Boeing Canada/De Havilland) DHC-8-400, DHC-8-401 and DHC-8-402 aeroplanes whose serial numbers fall within the enumerated ranges: S/N 4003, 4004, 4006, and 4008 through 4129 inclusive (Applicability). Those operators must ensure the modification is incorporated unless it has already been accomplished (Requirement: "Unless already accomplished").

Maintenance organisations and approved maintenance personnel are affected because the AD requires incorporation of a Modsum according to Bombardier Service Bulletin instructions. The SBs specified are SB84-27-33 (original issue 6 June 2007 and later approved revisions) and SB84-27-28 (Revision B dated 25 September 2007, and earlier versions for compliance per Note 1). The AD conditions acceptance of SB revisions on approval by the Chief, Continuing Airworthiness, Transport Canada, so the maintenance organisation must ensure that the specific SB revision used is an approved revision per that authority (Requirement; Note 1).

Pilots and flight crews are indirectly affected through the operational change the AD addresses. The background explains that the pre-modification indication behaviour can result in reduced roll authority perception and increased pilot workload in approach and landing phases, particularly when a cable disconnect occurs and only one caution light is illuminated above 165 knots (Background). After modification, the caution-light indications are to be consistent above and below 165 knots, changing the cockpit cue set pilots use in response to a spoiler fuselage cable disconnect.

Bombardier as the original equipment manufacturer is implicated because the Modsum and Service Bulletins are the designated corrective actions. The AD also notes that Modsum 4-126356 was installed in production on S/N 4130 and subsequent (Background), which affects manufacturers’ production records and how operators establish compliance status for later serial numbers.

Regulatory agencies are named: the Civil Aviation Safety Authority (CASA) is the issuing authority, with the AD signed by a CASA delegate, David Punshon (signature block). Transport Canada’s Chief, Continuing Airworthiness, is given a decision role in approving SB revisions that are acceptable for compliance (Requirement; Note 1; Note 2 reference to Transport Canada AD CF-2008-13).

Lessors, registrars and continuing airworthiness managers should also be considered affected parties because compliance is tied to aircraft records (installation of a Modsum and SB compliance), and the compliance period is measured in hours time-in-service after the AD effective date, which affects scheduling of maintenance and leasing arrangements (Compliance).

The AD creates a clear, narrow duty and a small set of conditional rights rooted in the text. Duty: operators of the applicable DHC-8 Series 400 aeroplanes must incorporate the specified Modsum into the spoiler cable disconnect sensing circuit "unless already accomplished" (Requirement). The duty is time-bound: the modification must be accomplished within 6000 hours time in service after the AD’s effective date (Compliance). The AD becomes effective on 10 April 2008, so the compliance clock runs from that date (Compliance; "This Airworthiness Directive becomes effective on 10 April 2008").

The AD specifies the means of compliance as incorporation of Modsum 4-110066 or Modsum 4-126356 per the corresponding Bombardier Service Bulletins. For S/N 4003, 4004, 4006 and 4008 through 4094 the means is incorporation of Modsum 4-110066 per SB84-27-33 original issue dated 6 June 2007 or later revisions approved by the Chief, Continuing Airworthiness, Transport Canada. For S/N 4095 through 4129 the means is incorporation of Modsum 4-126356 per SB84-27-28, Revision B dated 25 September 2007, or later revisions approved by the same Transport Canada official (Requirement a and b). The AD thus delegates a decision right to the Chief, Continuing Airworthiness, Transport Canada as to which later SB revisions are acceptable for compliance. The AD also allows for the prior use of specified earlier SB versions for Modsum 4-126356: installation in accordance with SB84-27-28 original issue (2 October 2006) or Revision A (30 April 2007) before the effective date is acceptable for compliance (Note 1). That is a specific right to count certain earlier work as meeting the AD.

The AD also de facto allows an operator to avoid taking action if the modification has "already been accomplished" before the AD,this is an explicit exception to the duty (Requirement preface "Unless already accomplished"). The AD does not describe the form in which proof of prior accomplishment should be recorded, but that exception is formally present in the directive.

The AD identifies the technical objective of the duty: to rework the sensing circuit so that caution light indications for spoiler fuselage cable disconnects are consistent above and below 165 knots (Background). The specified Modsum instructions are the authorised means to achieve that objective as of the AD’s issuance, subject to later SB revisions approved by the named Canadian official.

The AD is silent on the administrative processes for documenting compliance, seeking alternative methods of compliance, or notifying the regulator. It also does not specify who bears the cost of modification; the duty requirement creates a cost obligation for operators, but the AD text does not allocate payment responsibilities or describe funding mechanisms.

The AD text itself does not set out specific penalties, fines, or criminal sanctions for non-compliance. The document is titled and presented as an Airworthiness Directive issued by the Civil Aviation Safety Authority (signed by David Punshon, Delegate), and it states the effective date and the mandatory compliance requirement (Applicability; Requirement; Compliance). However, the AD text contains no express enforcement provisions, penalty schedules, or administrative sanction mechanisms within the document provided.

Because the AD is framed as an issuance by CASA and references approved Service Bulletins and Transport Canada approvals, the practical enforcement context ordinarily rests with the regulatory framework under which CASA operates. That framework is not reproduced in this document, so the AD does not itself describe how CASA will enforce compliance, how non-compliance is recorded, or what administrative or legal consequences follow a failure to accomplish the modification within the 6000 hours time-in-service window. The AD also does not specify reporting obligations, required documentation to prove compliance, or procedures to seek an alternative method of compliance or extension.

Given the absence of penalty language in the AD text, the document nonetheless creates an obligation that operators must follow. From the text one can only state that operators would be non-compliant with the AD if they do not incorporate the required Modsum within the specified time frame, or have not established that the modification had already been accomplished prior to the AD effective date (Requirement; Compliance). The AD does not indicate whether compliance will be verified by audit, inspection, or certificate action, nor does it set out an appeal or review mechanism within the text. Any enforcement mechanisms, sanctions, or compliance-verification processes would lie outside of the AD file text and would be defined in the broader regulatory regime that is not included in this instrument.

The instrument explicitly connects to at least one foreign airworthiness directive and to an external approval authority. The AD contains a note stating "Transport Canada AD CF-2008-13 refers" (Note 2). It also conditions acceptance of later Service Bulletin revisions on approval "by the Chief, Continuing Airworthiness, Transport Canada" (Requirement a and b). The AD, therefore, incorporates by reference the approvals and companion AD action taken by Transport Canada and anticipates reliance on that authority for acceptable revision approval. That creates an interaction where CASA’s AD prescribes a remedy but points to Transport Canada for the approval status of implementing documents.

Beyond that explicit cross-reference, the AD does not cite or quote Australian statutory provisions, Civil Aviation Regulations or other domestic legal instruments in the text provided. The AD does not specify how it modifies, supplements, or displaces any existing operating or airworthiness conditions in domestic aviation law or certificate conditions. The document also does not set out transitional arrangements concerning previously approved modifications or maintenance data other than the specific acceptance in Note 1 for earlier revisions of SB84-27-28 when Modsum 4-126356 was installed in accordance with those earlier instructions prior to the AD effective date.

The AD does not itself establish obligations for third parties such as lessees, registrars, or maintenance organisations beyond the technical requirement; interactions with contracts, lease agreements, or insurance policies are not addressed in the AD. The AD does identify production configuration as a factor: Modsum 4-126356 is said to have been installed in production on aircraft serial numbers 4130 and subsequent (Background). That observation interacts with the status of newly manufactured aircraft and their obligations under the AD, effectively excluding those later production aircraft because they already contain the corrective work.

In short, the instrument cross-refers to and relies on Transport Canada approvals and a Transport Canada AD. Any broader legal interactions with domestic aviation regulations, certification conditions, or civil enforcement frameworks are not contained within this AD text and would have to be sourced from the applicable regulatory statutes and CASA procedural documents outside this file.

The AD text includes and relies upon a short chain of service bulletin issuances and Modsum identifications and records certain production-installation facts. The documents and dates stated in the AD are the only amendment-history information contained in the source text. The timeline evident from the AD is:

• SB84-27-28 original issue dated 2 October 2006 (Bombardier). The AD states that installation of Modsum 4-126356 in accordance with SB84-27-28 original issue, dated 2 October 2006, or Revision A dated 30 April 2007, before the effective date of the Directive is acceptable for compliance with this Directive (Note 1).

• SB84-27-28 Revision A dated 30 April 2007 (Bombardier). Accepted per Note 1 if Modsum 4-126356 was installed before the AD effective date.

• SB84-27-28 Revision B dated 25 September 2007. The AD lists SB84-27-28 Revision B, dated 25 September 2007, or later revisions approved by the Chief, Continuing Airworthiness, Transport Canada, as the approved instructions for incorporating Modsum 4-126356 for S/N 4095 through 4129 (Requirement b).

• SB84-27-33 original issue dated 6 June 2007. The AD lists Bombardier Service Bulletin SB84-27-33, original issue dated 6 June 2007, or later revisions approved by the Chief, Continuing Airworthiness, Transport Canada, as the approved instructions for incorporating Modsum 4-110066 for S/N 4003, 4004, 4006 and 4008 through 4094 (Requirement a).

• Production modification note: Modsum 4-126356 has been installed in production on aircraft serial numbers 4130 and subsequent (Background). That fact sets a production cutover point relevant to applicability and indicates that Bombardier adopted the Modsum in the production line at or before S/N 4130.

• AD issuance and effective dates: the AD is signed by David Punshon, Delegate of the Civil Aviation Safety Authority, dated 18 February 2008, and the AD states that it becomes effective on 10 April 2008 (signature block; Compliance).

• Cross-reference to foreign AD: Note 2 indicates "Transport Canada AD CF-2008-13 refers", linking the domestic AD to companion Canadian action.

The AD does not itself list any subsequent amendments to this directive, nor does it describe any past amendments to the AD text. It records accepted previous SB revisions for compliance and the approved SB editions at the time of the statement. Any later amendments, superseding ADs or revised compliance times are not contained in the provided document.

The AD text contains no litigation history, case citations, or references to judicial decisions. It does not indicate any ongoing or concluded litigation concerning the AD, the Modsum corrections, the Service Bulletins, or the underlying design issue. The document is a regulatory directive limited to technical instructions, compliance timing, and references to manufacturer Service Bulletins and Transport Canada approvals. There are no legal proceedings, appeals, or tribunal references included in the text.

Therefore, based solely on the document provided, there is no recorded litigation history to summarise. Any disputes as to the directive’s validity, enforcement, the adequacy of the remedy, or the sufficiency of the compliance process are not reflected in this AD. To obtain litigation history one would need to consult court or tribunal records or administrative files outside the AD itself, but such material is not present in the source text and is therefore not reported here.

The AD contains several practical traps and detail points that can catch operators or maintenance planners if they read only superficially. These are drawn directly from the AD language and background.

1. Serial-number granularity. Applicability is confined to specific serial numbers: S/N 4003, 4004, 4006 and 4008 through 4129 inclusive. That list omits S/N 4001, 4002, 4005, 4007 and others; operators must verify aircraft serials precisely. The AD does not apply to aircraft outside that explicit list (Applicability).

2. Two separate Modsum pathways. There are two different Modsums depending on serial-number blocks: Modsum 4-110066 for S/N up to 4094 and Modsum 4-126356 for S/N 4095-4129. Using the incorrect Modsum for the serial-number block would mean non-compliance with the AD’s specified remedy (Requirement a and b).

3. Accepted earlier installations. Note 1 allows Modsum 4-126356 installations performed using SB84-27-28 original issue (2 October 2006) or Revision A (30 April 2007) before the AD effective date to satisfy the AD. That means retrospective proof becomes important: if an operator claims prior compliance based on those earlier SBs, the AD accepts that,but the burden of proof for "already accomplished" rests with the operator’s records, although the AD does not prescribe the form of evidence (Note 1; Requirement preface "Unless already accomplished").

4. Approved revisions required. The AD permits later SB revisions only if they are approved by the Chief, Continuing Airworthiness, Transport Canada. The AD therefore requires checking that the specific SB revision used is approved by that named official. Operators cannot rely on an arbitrary later SB revision unless it has the specific approval the AD requires (Requirement a and b).

5. Compliance measured in hours in service. The compliance time is given as "within 6000 hours time in service after the effective date of this Directive." This is not a calendar deadline. High-utilisation aircraft will hit 6000 hours quicker than low-utilisation aircraft, so scheduling must be based on time-in-service accounting rather than a target date (Compliance).

6. Effective date versus signature date. The AD was signed on 18 February 2008 but becomes effective on 10 April 2008. Planning must reference the effective date for the compliance clock (signature block; Compliance).

7. Production cutover. Modsum 4-126356 was installed in production on S/N 4130 and subsequent. The AD covers only up to S/N 4129, so S/N 4130 and later are out of the applicability because they already have the Modsum fitted in production. Operators of such later aircraft must still verify production records to confirm the factory installation (Background).

8. The operational symptom and the speed band. The specific symptom is that only the ROLL SPLR INBD HYD caution light is illuminated until speed decreases below 165 knots, at which point ROLL SPLR OUTBD HYD is also illuminated. The AD targets consistency of caution-light indication above and below 165 knots. That numeric threshold is operationally significant for pilots and must be noted when assessing the risk during different phases of flight (Background).

9. No enforcement/administrative detail in the AD. The AD does not explain how compliance will be documented, who must be notified, or what evidence is required. Operators should not assume the AD handles those administrative steps and should plan to keep auditable maintenance records showing incorporation of the Modsum (Requirement; Compliance).

10. Cross-jurisdiction references. The AD’s acceptance of SB revisions and its reference to Transport Canada AD CF-2008-13 means operators should confirm whether their chosen SB revision has the necessary Transport Canada approval. Assuming that an SB revision is acceptable without confirmation could be a compliance pitfall (Requirement; Note 2).

The AD prescribes a narrow, practical compliance path which can be implemented as follows, grounded in the AD’s own instructions.

1. Identify applicable aircraft. Confirm serial numbers against the AD’s Applicability list: DHC-8-400, -401 and -402 with S/N 4003, 4004, 4006 and 4008 through 4129 inclusive. Exclude aircraft outside that list and verify production records for S/N 4130 onward because the AD states Modsum 4-126356 was installed in production on S/N 4130 and subsequent (Applicability; Background).

2. Determine current modification status. Check maintenance records and logbooks to ascertain whether Modsum 4-110066 or Modsum 4-126356 has already been incorporated. The AD’s directive attaches an exception "Unless already accomplished" to the modification duty. If the Modsum was installed prior to the AD effective date in conformity with the SB versions noted in Note 1 and Requirement b, that prior work is acceptable for compliance.

3. Select the correct Modsum and SB. For aircraft S/N 4003, 4004, 4006 and 4008-4094, incorporate Modsum 4-110066 using Bombardier SB84-27-33 original issue dated 6 June 2007, or a later revision of that SB expressly approved by the Chief, Continuing Airworthiness, Transport Canada (Requirement a). For aircraft S/N 4095-4129, incorporate Modsum 4-126356 using Bombardier SB84-27-28 Revision B dated 25 September 2007, or a later revision of SB84-27-28 approved by the Chief, Continuing Airworthiness, Transport Canada (Requirement b). If Modsum 4-126356 was incorporated earlier using SB84-27-28 original issue (2 October 2006) or Revision A (30 April 2007) prior to the AD effective date, that earlier work is explicitly acceptable (Note 1).

4. Verify SB revision approvals. The AD conditions acceptance of later SB revisions on approval by the Chief, Continuing Airworthiness, Transport Canada. Before using a SB revision later than the specified ones, confirm that Transport Canada’s Chief, Continuing Airworthiness has approved that revision as acceptable for compliance with this AD (Requirement a and b).

5. Schedule the work within the compliance window. The AD sets the compliance time as within 6000 hours time in service after the AD effective date of 10 April 2008. Plan maintenance to ensure that the modification is physically incorporated on each affected airframe before the aircraft accrues 6000 hours TIS from that effective date (Compliance). Use objective time-in-service records to calculate remaining compliance hours.

6. Use approved personnel and procedures. Perform the Modsum incorporation in accordance with the Bombardier SB instructions selected, applied exactly as approved. Use appropriately authorised maintenance organisations and certificated personnel able to implement structural/electrical modifications as defined in the SB procedure set. The AD text makes the SB installation instructions the approved method for effecting the Modsum (Requirement). Although the AD does not specify who may do the work, practical compliance requires use of maintenance organisations authorised to carry out such modifications.

7. Record and retain evidence. The AD does not set out a specific form of compliance evidence, but operators should create and keep maintenance entries, engineering orders, SB compliance statements, and any approvals from Transport Canada establishing which SB revision was used. Where Note 1 is relied upon to claim pre-AD compliance, documentation showing the date of incorporation and SB revision used will be necessary to demonstrate that the earlier installation meets the AD’s acceptance criteria.

8. Confirm operational expectations. After modification, verify that the sensing circuit rework does produce the intended consistent caution-light behaviour for spoiler fuselage cable disconnect events above and below 165 knots, as described in the Background. Operational checks, bench testing, and a post-modification flight or system test (as required by the SB) should be completed to confirm the modification's effect on the caution-light indications.

9. Consider regulatory liaison where necessary. If there is any uncertainty about the acceptability of a particular SB revision, an alternative method of compliance, or the interpretation of "already accomplished," contact the Civil Aviation Safety Authority or consult the referenced Transport Canada approvals. The AD itself defers to the Transport Canada Chief, Continuing Airworthiness for SB revision approval (Requirement), so confirmation from the relevant authority will reduce compliance risk.

10. Treat production-built aircraft appropriately. For aircraft S/N 4130 and subsequent, which the AD states had Modsum 4-126356 installed in production, verify production records to demonstrate compliance; you do not need to rework aircraft that already contain the Modsum as part of their original configuration (Background).