AD/DHC-8/104 - Elevator Trim and Gust Lock Chain Failure

The central concept is an airworthiness directive, a mandatory regulatory instrument issued under delegated powers in the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations (CASR). An AD imposes a corrective action to address an unsafe condition in an aircraft type. The unsafe condition here is hydrogen embrittlement cracking in elevator trim and gust lock chains. Hydrogen embrittlement is a metallurgical process where atomic hydrogen diffuses into the metal, causing a loss of ductility and sudden cracking under stress, particularly in high-strength steels. The cracking is not visible to flight crew because the trim chain is inside the tail cone and there is no cockpit warning for a trim chain failure - the first indication may be abnormal control loads or inability to achieve proper trim during takeoff rotation. The “RC 25” identifier is a manufacturer’s marking on chains and chain cable assemblies that are considered not susceptible to hydrogen embrittlement cracking (or have been treated to prevent it). The AD assumes that chains without this identifier are the ones at risk. The aircraft flight manual temporary amendment is a procedural change that alerts flight crew to perform elevator trim checks before takeoff, as a workaround until the chains are replaced. The gust lock is a mechanism that locks the flight control surfaces (elevator) when the aircraft is parked; the trim system sets the neutral position of the elevator for flight. Both share a common chain drive in the DHC-8 design. The AD’s terminating action concept means that once the physical inspection and replacement are done, the AFM amendment is no longer needed because the underlying risk is eliminated. The AD also incorporates by reference Bombardier Service Bulletin 8-27-105 Revision A, which contains the detailed inspection procedures and criteria. Operators are permitted to use later Transport Canada approved revisions of that SB, giving some flexibility, but only if Transport Canada specifically approves them - not any later version by Bombardier alone. This creates a regulatory hierarchy where foreign (Canadian) airworthiness approval is recognised.

The AD directly affects owners and operators of Bombardier DHC-8 aircraft of Models 102, 103, 106, 201, 202, 301, 311, 314 and 315, with serial numbers 003 through 610. This covers the original Dash 8 Series 100, 200, and 300 aircraft, but not the later Series 400 (Q400). Given the serial number range (003 to 610), this is a large fleet of approximately 600 airframes, many of which remain in service with regional airlines, freight operators, and government agencies in Australia and operated by Australian certificate holders. The compliance obligations fall on the “operator” as defined under the Civil Aviation Act - typically the entity holding the air operator’s certificate (AOC) for the aircraft. In a lease arrangement, the lessee operator is responsible unless the lease delegates maintenance to the lessor. The AD also affects approved maintenance organisations (AMOs) that perform inspections and replacements; they must have access to the Bombardier SB and must train their technicians to identify the RC 25 marking. Parts suppliers and distributors are indirectly affected because Requirement 3 prohibits the installation of chains without RC 25 as replacements - effectively creating a ban on selling non-conforming parts for fitment. The flight crew are affected because they must be briefed on the AFM amendment and the elevator trim check procedure; this imposes a recurrent training burden until the terminating action is completed. The AD also affects Bombardier (now part of De Havilland Canada, formerly Viking Air) as the service bulletin originator; and Transport Canada as the design approval authority whose AD is referenced. Insurance underwriters and aviation risk managers for operators of the affected fleet will factor compliance into premiums and risk assessments. Finally, the AD may affect the resale value of aircraft that have not yet completed the inspection and replacement, as non-compliance is a continuing airworthiness issue that must be disclosed.

The primary duty is on the operator to ensure compliance with each of the three requirements within the specified time frames. Under Requirement 1, the operator must physically insert the correct temporary amendment into the AFM for each affected aircraft. That amendment must be the one identified in the table: for example, Model 102/103/106 uses PSM 1-81-1A Temporary Amendment No. 9; Model 311 uses PSM 1-83-1A No. 15; etc. The operator must also brief flight crew - this likely means a written briefing or training record. Under Requirement 2, the operator must perform (or arrange) a visual inspection of the elevator gust lock/trim chains to see if they bear the RC 25 identifier. The inspection method is not fully detailed in the AD; it references Bombardier SB 8-27-105 Revision A for procedures, which likely includes access instructions, what to look for, and acceptance criteria. If a chain or chain cable assembly lacks the identifier, the operator must replace it. The operator may choose to use later Transport Canada approved revisions of the SB, but not unapproved revisions. Under Requirement 3, the operator has a continuing duty after the effective date never to install a chain or chain cable assembly that lacks the RC 25 identifier as a replacement on any aircraft covered - even if the aircraft originally passed the Requirement 2 inspection. The operator has a right to remove the temporary amendment from the AFM once Requirement 1’s terminating action is completed (i.e., inspection done and non-RC25 chains replaced). That right is conditional on full compliance with Requirement 2. The operator also has the right to rely on later approved revisions of the service bulletin, which may have different inspection intervals or methods, provided they are approved by Transport Canada. The AD does not grant any right to apply for an alternate means of compliance or extension; that would be handled under separate CASA processes. The duties are strict; there is no fault element mentioned. The operator is also obliged to keep records of compliance (insertion of amendment, inspection results, part numbers of replaced chains). The AD does not directly impose duties on maintenance personnel, but under the CASR they must be authorised and must follow the approved data.

The source document (the AD itself) does not specify penalties. However, under the broader legislative framework of the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations 1998, failure to comply with an airworthiness directive is a serious offence. Specifically, CASR 39.008 provides that a person must not operate an aircraft that is not in an airworthy condition, and CASR 42.230 requires that maintenance be performed in accordance with approved data, which includes ADs. Operating an aircraft in breach of an AD can lead to civil penalty proceedings under Part 4A of the Civil Aviation Act, with maximum penalties currently up to $1.1 million for individuals and $11 million for corporations per contravention (indexed). Criminal penalties may also apply if the breach is reckless or intentional and results in endangerment. CASA can issue a direction to ground the aircraft (grounding order) under section 26 of the Act, which is a common immediate enforcement tool. The AD itself does not mention penalties but rather states the compliance requirements as mandatory. The practical enforcement angle: CASA inspectors during routine surveillance or ramp checks will look for AD compliance as a standard part of checking the aircraft’s maintenance release and logbooks. The AD is referenced in the aircraft’s continuing airworthiness record. Non-compliance could also affect the validity of the aircraft’s certificate of airworthiness and the operator’s AOC. Insurance policies typically exclude coverage for operations in breach of an AD. The AD’s 30-day compliance window for Requirement 1 is tight; missing that deadline could result in enforcement action even if the physical inspection is done later. Because the AD has been in effect since December 2005, enforcement actions are now historical unless a newly imported aircraft has never complied. The AD does not provide any defence or exception; strict liability is standard for AD compliance.

This AD operates within the hierarchy of Australian aviation law. The primary legislation is the Civil Aviation Act 1988, which empowers CASA to issue airworthiness directives under regulations. The specific regulation is CASR Part 39 (Airworthiness Directives), which provides the legal framework for the issuance, notification, and enforcement of ADs. This AD is a legislative instrument within the meaning of the Legislation Act 2003, though it is usually not registered on the Federal Register of Legislation due to exceptions for operational documents; it is published on the CASA website. The AD also interacts with the Civil Aviation Safety Regulations Part 21 (Certification of aircraft) and Part 43 (Maintenance). Compliance with the AD is a condition for maintaining the aircraft’s Certificate of Airworthiness. The AD references Transport Canada AD CF-2005-38, showing interaction with foreign airworthiness requirements. Under bilateral agreements between Australia and Canada, CASA recognises Transport Canada’s design approvals. This AD essentially adopts the Canadian AD with identical requirements, but CASA issues its own AD to make it legally binding in Australia. The service bulletin (Bombardier SB 8-27-105) is not law itself but becomes mandatory when incorporated by reference into the AD. The AD also interacts with Part 42 of CASR (Continuing Airworthiness) which requires operators to have a system to manage mandatory continuing airworthiness information, including ADs. The AD does not mention any interaction with workplace health and safety laws, but maintenance personnel performing inspections and replacements must comply with WHS requirements. There could be overlap with Environment Protection Act provisions if disposing of old chains containing hazardous materials, though unlikely. The AD does not affect consumer laws directly. If an aircraft is operating under a foreign registration but in Australian territory, the operator must still comply with Australian ADs under the Air Navigation Regulations.

The source document does not provide any amendment history. AD/DHC-8/104 appears to be the original issue dated 10 November 2005, effective 22 December 2005. The user’s input contains the full text of the AD itself (as an HTML table and image). There is no indication of any amendments or revisions to this AD. In practice, CASA may have reissued or superseded it with a later AD number (e.g., AD/DHC-8/104 Amendment 1) or withdrawn it after the terminating action was completed by most operators and the fleet aged out. However, without the source mentioning any subsequent amendments, I cannot assert that any exist. The AD references Bombardier SB 8-27-105 Revision A, dated 13 September 2005, which itself may have superseded earlier revisions, but that is a manufacturer’s document, not an amendment to the AD. The AD also notes that later Transport Canada approved revisions of the SB may be used, so the SB itself has a possible amendment path, but not the AD. The AD’s terminating action effectively means that once an individual aircraft completes the inspection and replacement, the AD is no longer recurring for that aircraft. Many aircraft in the affected serial range are now likely retired or modified. The Civil Aviation Act requires any subsequent amendment to an AD to be published in the same manner as the original. Without data, I cannot speculate on whether CASA downgraded or removed this AD. For compliance record-keeping purposes, operators should check the current CASA AD listing to see if AD/DHC-8/104 remains in force, has been superseded by a more recent AD number, or has been cancelled. My analysis is limited strictly to the text provided.

The source document does not refer to any litigation, and I am not aware of any reported case involving AD/DHC-8/104. Airworthiness directives rarely become the subject of litigation in Australia because the regulatory framework gives CASA broad discretion and compliance is effectively enforced through administrative action (grounding, suspension) rather than court proceedings except for civil penalties. The most common type of AD litigation in Australia is judicial review of CASA’s decision to issue an AD, but that requires the applicant to demonstrate jurisdictional error or unreasonableness. Given this AD dated from 2005 and addressed a specific safety issue with a well-understood failure mechanism (hydrogen embrittlement), and the compliance burden was relatively low (inspection and possible part replacement), a legal challenge is improbable. The AD incorporates the Bombardier SB as an adjunct; any product liability claims against Bombardier for the defective chains would be in contract or tort, not under the AD itself. The operator’s duty to replace chains without RC 25 could theoretically lead to disputes over the cost of replacement if the aircraft is leased, but that is a private law matter, not litigation interpreting the AD. The absence of litigation history in the source does not mean no legal proceedings ever occurred; it simply means none are referenced. My instructions prohibit me from inventing or citing any cases not named in the source. Therefore, under this heading I can only state that the source contains no litigation history, and I cannot supplement from external knowledge, even if widespread. The reader must assume that any disputes were resolved without published judgments or that the AD was complied with universally.

Several aspects of this AD could catch operators and maintenance organisations unprepared. First, the compliance time for Requirement 2 (inspection and replacement) is “before accumulating 6,000 hours flight time from the effective date; or within 36 months of the effective date, whichever occurs earlier.” The effective date is 22 December 2005. For an aircraft that already had more than 6,000 hours total time on that date, the operator must consider “accumulating flight time from the effective date” - meaning the AD’s 6,000-hour clock starts from that date, not from new. This could create confusion if operators mistakenly add total flight time from first flight. Second, Requirement 1 must be completed within 30 days of the effective date - a very short window - and covers all affected aircraft regardless of usage. An operator that did not immediately insert the AFM amendment would have been technically non-compliant even if the aircraft was not operated. Third, the AFM amendment table requires careful matching of model variant with temporary amendment number. For example, the 201 and 202 models have different amendment numbers (No. 11 and No. 10 respectively) even though both use PSM 1-82-1A; mixing them up would constitute non-compliance. Fourth, the “RC 25” identifier must be visually confirmed; but some chains may have the identifier worn off or obscured, which could lead to unnecessary replacement if not found. The AD does not address acceptable methods to confirm identity if the marking is illegible. Fifth, the prohibition in Requirement 3 is perpetual - even after the terminating action, you cannot install a non-RC25 chain as a replacement. This means parts inventory and procurement systems must be updated to only order RC25-marked chains. If a maintenance organisation inadvertently fits a non-RC25 chain from stock bought before the AD, that is a breach regardless of intention. Sixth, the AD’s background states that failures are not annunciated to the flight crew, so the only protection is the pre-takeoff trim check from the AFM amendment. If that amendment is removed prematurely (before inspection is completed), the aircraft could be operated with a latent failure risk. The terminating action is defined as completing the inspection and replacing chains - not just doing the inspection. So an operator who inspects and finds only RC25 chains still cannot remove the AFM amendment? The AD says “after completing the inspection and replacing the chains that do not have the RC 25 identifier.” That implies if all chains have RC25, no replacement is needed, yet the phrase “replacing the chains that do not have the RC 25 identifier” would be vacuously true. Strictly, the condition is that all chains lacking RC25 must be replaced. If none lack it, that condition is satisfied. So removal is permitted after inspection. But the wording could cause doubt. Seventh, the AD allows later Transport Canada approved revisions of the SB; operators cannot use later Bombardier revisions without that Canadian approval, even if Bombardier publishes a better method. Finally, for aircraft imported into Australia after December 2005, the AD applies immediately on first Australian registration; they must comply with the serial number range regardless of where they were previously registered.

Compliance requires careful documentation and coordination between flight operations and maintenance. The practical steps are as follows.

Step 1: Identify all applicable aircraft in your fleet by model and serial number (003 to 610). Check the table for the correct PSM number and Temporary Amendment number for each model variant. Obtain the appropriate Temporary Amendment from Bombardier or through the aircraft manufacturer’s distribution system. Within 30 days of 22 December 2005 (or within 30 days of the aircraft’s first operation under Australian registration if later), physically insert a copy of the Temporary Amendment into the aircraft flight manual (AFM) for each aircraft. The amendment should be inserted as a permanent part of the AFM until terminated. After insertion, brief all flight crew who will operate the aircraft on the requirements of the amendment, specifically the need to conduct elevator trim checks before takeoff. Record the briefing in crew training records.

Step 2: For each aircraft, determine the time since the effective date. Calculate the deadline for Requirement 2: either on or before the earlier of (i) accumulating 6,000 flight hours from the effective date (tracked by a new hours counter from 22 December 2005), or (ii) 36 months from the effective date (22 December 2008). For an aircraft that was grounded or stored for a period, the 6,000-hour clock may not run if no hours accumulate, but the 36-month deadline is absolute. Obtain a copy of Bombardier Service Bulletin 8-27-105 Revision A, dated 13 September 2005. Confirm that it is the version approved by Transport Canada (since the AD accepts “later Transport Canada approved revisions” - check if any later revision has been approved). Perform a visual inspection of the elevator gust lock and trim chains and chain cable assemblies. The SB will specify access panels, inspection criteria, and how to locate the RC 25 identifier. If you cannot find the identifier, assume the chain is non-conforming. For any chain or chain cable assembly that does not have the RC 25 identifier, remove and replace it with a part that does bear the RC 25 identifier. The replacement part must be a new or serviceable part that is marked RC 25. The AD does not require a specific part number; only the identifier matters. Record the inspection results, including serial numbers of chains removed and fitted, and maintain in the aircraft maintenance log.

Step 3: After completing the inspection and any necessary replacements on an aircraft, the terminating action for Requirement 1 is satisfied. Remove the Temporary Amendment from the AFM. Ensure that the removal is noted in the AFM record and the flight crew are advised that the amendment is no longer effective.

Step 4: Establish a continuing policy that no chain or chain cable assembly lacking the RC 25 identifier shall ever be installed as a replacement on any aircraft covered by this AD. This means updating your parts purchasing and issue procedures to reject non-RC25 parts. Also ensure your maintenance manual and task cards reference this prohibition.

Step 5: Document all actions for each aircraft: the insertion and removal dates of the AFM amendment, the date of inspection, the flight hours at inspection, the inspection results, part numbers and identifiers of replaced chains, and evidence of flight crew briefing. Keep these records for the life of the aircraft as part of the continuing airworthiness record system. For any future aircraft entering the fleet that falls within the serial number range, perform compliance immediately upon registration; the 30-day and 36-month deadlines run from the effective date of the AD, not from the date of import, so you may need to treat them as already overdue. In that case, immediate compliance with all three requirements is necessary. Note that the AD does not allow alternative means; if you cannot obtain RC25 chains, you may need to ground the aircraft until they are sourced. Finally, periodically check the CASA website or your AD compliance service to see if this AD has been superseded or withdrawn, as older ADs are occasionally removed once the fleet has been fully modified. However, absent any amendment, you must treat it as continuing to apply.