AD/DHC-8/119 - Main Landing Gear Up-Lock Assembly

An Airworthiness Directive is a legally enforceable order issued by CASA under the Civil Aviation Act 1988 or associated regulations, compelling operators and owners of Australian-registered aircraft to rectify identified unsafe conditions. Non-compliance renders the aircraft unairworthy and exposes the operator to enforcement action. This directive focuses on the main landing gear up-lock assembly, a mechanical component that holds the landing gear in the retracted position during flight and must release cleanly when gear extension is commanded. The assembly consists of a latch, roller, and associated parts that engage and disengage under hydraulic and spring forces.

The source identifies three part numbers for the up-lock assembly. Part number 46500-3 was the original production unit, now discontinued. Part number 46500-5 was introduced as a substitute but the source notes its design is “very similar” and could be subject to the same wear failure. Part number 46500-7 is a modified assembly that is the terminating action: once both sides are replaced with this part, the entire AD is satisfied and no further inspections or replacements are required under this directive.

A key failure mode described is the presence of a wear groove in the up-lock latch lower jaw. The directive requires measurement of groove depth to 0.001 inch accuracy and sets a mandatory replacement threshold at 0.007 inches. The source does not explain how that threshold was derived, but it presumably represents the depth at which the hook can no longer reliably disengage. Another failure mode is the omission of a low-friction liner on the up-lock roller. The liner reduces friction during disengagement; without it, the roller may bind and prevent unlatching. The directive requires inspecting the roller for that liner and, if absent, replacing the roller with a new one of the same part number (46575-1) that does include the liner.

Compliance intervals are expressed in two metrics: hours air time and flight cycles, with the stricter of the two applying (the one that occurs first). For the initial replacement of up-lock assemblies, the interval is 2,500 hours or 3,000 flight cycles. For the recurrent inspection of the up-lock latch lower jaw on P/N 46500-5 assemblies, the interval after initial compliance is 400 hours or 480 flight cycles, a significantly shorter period. The directive does not explain the rationale for the difference, but it likely reflects the higher risk of rapid wear propagation once a groove begins to form. The concept of “terminating action” is central: it creates a clear end point for compliance burden, incentivising operators to install the final modification rather than remain in a recurring inspection loop.

The primary duty holders are the operators and owners of the affected aircraft. The applicability clause targets Bombardier Inc. DHC-8 Models 400, 401, and 402 with serial numbers 4001 and 4003 through 4087, fitted with main landing gear up-lock assembly part numbers 46500-3 or 46500-5. Aircraft that have already been fitted with P/N 46500-7 at production or by a previous modification are excluded from the applicability section, as noted in the background: “The applicability section of this directive is also revised to reflect production aircraft that have incorporated the terminating action.” So the directive does not affect aircraft that rolled off the line with the final part number already installed. This is a standard feature of airworthiness directives: they carve out aircraft that have already met the intended end state.

Within the affected fleet, the compliance burden falls on several groups. Flight crews must be advised of the AFM changes and be familiar with the abnormal procedure for a single gear failure to extend. Maintenance organisations must schedule and perform the inspections and replacements, including the specialised measurement of wear groove depth to 0.001 inch accuracy using appropriate tools. Engineering staff must ensure that maintenance manual Chapter 32-31-21 tasks are followed precisely and that the Bombardier Alert Service Bulletin A84 32 15 is referenced for the roller liner inspection. Record-keepers must log each compliance event and note the terminating action when completed.

The economic impact is concentrated on operators of a specific regional turboprop aircraft type. The directive imposes direct costs: purchase of replacement up-lock assemblies (P/N 46500-7) and rollers, labour for inspections and replacements, aircraft downtime for scheduled maintenance, and the administrative burden of AFM revision. Operators who elect not to install the terminating part must continue the recurrent 400-hour/480-cycle inspections, which increases lifetime compliance costs and maintenance scheduling complexity. The directive thus creates an incentive to invest in the more expensive but less burdensome final modification.

Indirectly, the directive affects lessors, insurers, and aircraft trading markets. An aircraft that has had the terminating action performed is more attractive to buyers and lessors because it eliminates ongoing inspection obligations. Conversely, an aircraft still operating with P/N 46500-5 and its shorter inspection interval may face lower residual value or higher insurance premiums. Parts suppliers and overhaul shops benefit from increased demand for P/N 46500-7 assemblies and P/N 46575-1 rollers. Bombardier, as the original manufacturer, may have supplied the service bulletin and terminating modification, potentially generating revenue from part sales.

The directive interacts with the broader civil aviation regulatory system. CASA exercises its delegated authority through James Coyne, the delegate who signed the directive on 17 March 2006. The directive is one of many addressing landing gear issues on various aircraft types; it does not exist in a vacuum but forms part of the continuing airworthiness management regime under Civil Aviation Regulation 1988 Part 4A or equivalent CASR provisions.

The AD imposes four key duties on operators. Duty one: within 30 days of 11 May 2006, amend the Aircraft Flight Manual (PSM 1-84-1A) by inserting the specified abnormal procedure on page 4-21-1. This procedure must be communicated to all flight crews. Duty two: also within 30 days, inspect both main landing gear up-lock rollers for the presence of an inner low-friction liner, per Bombardier Alert Service Bulletin A84 32-15. If any roller lacks the liner, it must be replaced with a new P/N 46575-1 roller. Duty three: replace the main landing gear up-lock assemblies (P/N 46500-3 or 46500-5) with new or overhauled units of the same or later part number, initially before the assembly accumulates 2,500 hours or 3,000 flight cycles, and thereafter at the same interval. Duty four: for assemblies already of part number 46500-5, before they reach 2,500 hours/3,000 cycles and then every 400 hours/480 cycles, inspect the up-lock latch lower jaw for a wear groove measured to 0.001 inch accuracy; if groove depth exceeds 0.007 inches, replace the assembly with P/N 46500-7; also inspect the roller for free rotation and replace if binding.

The obligations are ongoing until the terminating action is completed. The right to terminate arises when both left and right up-lock assemblies have been replaced with P/N 46500-7. Upon that event, the operator may remove the abnormal procedure from the AFM (requirement 1(b)), and all subsequent inspections and replacements under this directive are no longer required. This is a voluntary right: operators may choose to remain with the recurring inspection regime if they prefer cash flow management over a one-off capital outlay, though the shorter inspection interval for P/N 46500-5 makes that choice economically inferior unless the aircraft is near the end of its life.

The AD does not explicitly mention a right to apply for alternative means of compliance, but the broader regulatory framework (Civil Aviation Safety Regulations 1998 Part 39) typically permits operators to propose an equivalent level of safety method subject to CASA approval. Such alternatives must be formally documented and accepted before deviating from the directive. Operators therefore have a procedural right to seek flexibility, but must bear the burden of proving equivalence.

Another implied right is the ability to delegate the compliance work. The directive does not prescribe who must perform the tasks; it simply mandates the outcomes. Operators may contract with licensed aircraft maintenance engineers or approved maintenance organisations. However, any modification to a type design or use of non-original parts would require separate approval.

The duty to advise flight crews is notable. It is not enough for the maintenance team to insert the AFM pages; the operator must actively notify pilots of the change. This implies a record of communication, such as a circular or briefing, and may be verified during a CASA audit. Failure to advise creates a separate compliance gap even if the physical AFM is updated.

The AD itself does not specify penalties, but it is issued under the Civil Aviation Act 1988 and associated regulations, which carry substantial enforcement consequences for non-compliance. Operating an aircraft that does not conform to an applicable airworthiness directive is a breach of the condition of the aircraft’s certificate of airworthiness. Under Civil Aviation Regulation 1988 regulation 37 (or equivalent CASR provisions), the aircraft is deemed unairworthy. A person who operates or permits the operation of an unairworthy aircraft may face penalties including fines (currently up to 200 penalty units for an individual, 1,000 penalty units for a body corporate, with a penalty unit indexed annually) and, in serious cases, imprisonment. The aircraft may be grounded until compliance is achieved.

CASA has a range of enforcement options short of prosecution. It may issue a show-cause notice, impose a condition on the certificate of airworthiness, suspend or revoke the certificate, or issue an enforceable undertaking. In practice, CASA often works with operators to achieve compliance within a reasonable time, but the AD’s compliance times are considered mandatory deadlines. The 30-day requirement for AFM amendment and roller liner inspection, for example, is not aspirational; failure to meet it exposes the operator to immediate enforcement.

The AD’s effective date is 11 May 2006. From that date, non-compliant aircraft may not be operated in Australian airspace. If an operator inadvertently operates without having performed the AFM amendment or the roller inspection within 30 days, each day of operation constitutes a separate offence. The risk is heightened because the AD applies to specific serial numbers; any operator of the affected models must verify whether their aircraft are caught.

Enforcement may also arise indirectly through liability. If an aircraft suffers a landing gear malfunction and an investigation reveals non-compliance with this AD, the operator could face civil liability for damages, reduced insurance coverage, or criminal negligence charges. The AD record becomes a key piece of evidence. In the United States, the National Transportation Safety Board has repeatedly cited failure to comply with airworthiness directives as a probable cause factor; Australian courts would likely treat compliance as a standard of care.

The CASA delegate who signs the AD has enforcement authority delegated under the Act. The directive is signed by James Coyne, Delegate of CASA. CASA may also issue a direction to ground the aircraft if non-compliance is discovered during a ramp inspection or audit. The cost of grounding (lost revenue, passenger disruption, reputational damage) far outweighs the compliance costs, creating a strong economic incentive to comply.

Operators should note that compliance is not optional. The AD uses mandatory language: “amend all copies”, “replace”, “inspect”. There is no provision for waiving the requirements. The only relief is the terminating action, which, once performed, ends all obligations. Until then, operators must strictly adhere to the stated intervals, and documentation must show that the actions occurred within the required time windows.

This AD is part of a hierarchy of continuing airworthiness regulations. It sits under the Civil Aviation Act 1988 and the regulations made under it, particularly the Airworthiness Directives provisions either in Civil Aviation Regulations 1988 Part 4A or Civil Aviation Safety Regulations 1998 Part 39. It does not replace or override those regulations; rather, it particularises them for a specific unsafe condition. Any pre-existing requirements in the regulations regarding maintenance records, technical log entries, or defect reporting continue to apply.

The AD cross-references Bombardier Alert Service Bulletin A84 32-15, dated 4 February 2002 (or later revisions approved by Transport Canada). That service bulletin is not itself legally binding, but compliance with the AD requires following its “Accomplishment Instructions” for the roller liner inspection. Similarly, the AD references DHC-8 Series 400 Aircraft Maintenance Manual PSM 1-84-2, tasks in Chapter 32-31-21, for the replacement of up-lock assemblies and the inspection of wear groove depth. The maintenance manual is a manufacturer’s document; the AD elevates certain tasks within it to mandatory status. Operators must ensure they have the current revision of the manual, as the AD refers to it by title and chapter.

The AD also interacts with Transport Canada AD CF-2002-13R2, which is noted in the source. This Australian AD likely mirrors or adapts the Canadian directive because Bombardier’s type certificate originates from Canada, and CASA typically recognises Transport Canada’s findings. For Australian-registered aircraft, the CASA AD is the controlling legal document; however, if the aircraft is also registered in another state that has adopted the Canadian AD, operators must comply with both. Differences between the two directives could create conflicting requirements; operators should verify whether the Australian AD is equivalent or imposes additional steps. The source does not elaborate, but the note “TC AD CF-2002-13R2 refers” suggests the Australian directive is aligned with its Canadian counterpart.

The AD interacts with aircraft leasing and sale documentation. A lessee is typically contractually obliged to comply with all airworthiness directives. The lessor may require evidence of compliance as a condition of the lease. When an aircraft is sold, the purchaser’s pre-purchase inspection will check for AD compliance; the terminating action (P/N 46500-7) is a valuable attribute because it prevents future inspection obligations. The AD thus creates a tangible asset difference between aircraft that have completed the terminating action and those that have not.

The AD does not directly interact with foreign airspace requirements, but if a DHC-8 Series 400 registered in Australia operates overseas, the local aviation authority may require evidence of compliance with all applicable ADs. The US FAA, for example, may require that foreign-registered aircraft operating into the US comply with its own ADs or show that the home state’s AD provides an equivalent level of safety. The Australian AD’s harmonisation with Transport Canada’s directive assists in cross-border acceptance.

The source document is AD/DHC-8/119, issued 17 March 2006, effective 11 May 2006. The background section states: “The applicability section of this directive is also revised to reflect production aircraft that have incorporated the terminating action.” This indicates that this version of the directive is not the original, but a revision that updated the applicability to exclude aircraft that already had P/N 46500-7 installed at production. The source does not provide the original text or prior amendment dates, so we cannot reconstruct the full lineage. However, the reference to Transport Canada AD CF-2002-13R2 suggests that the Australian directive was first issued sometime after the Canadian AD took effect, possibly in 2002 or 2003. AD CF-2002-13R2 is itself an amended version of an earlier directive, as indicated by the “R2” (second revision) in its title.

The source contains no subsequent amendments after the 17 March 2006 signature. ADs are typically numbered sequentially by CASA: AD/DHC-8/119 is the 119th directive for the DHC-8 series, implying a series of prior and subsequent directives addressing other issues. This particular directive has been allocated number 5/2006 in the annual numbering system, meaning it was the fifth AD issued in 2006 for this aircraft type.

The note on page 2 of the source says “TC AD CF-2002-13R2 refers.” That directive may have had its own amendment chain, but the Australian AD does not incorporate those amendments by reference; it only notes the relationship. Operators looking for the full technical basis would need to consult both the Canadian and Australian documents.

The compliance language includes “unless previously accomplished” for requirements 1(a) and 3, meaning that any operator who had already amended the AFM or inspected the roller liner before the effective date need not do so again. This is a standard grandfathering provision to avoid redundant work. The source does not specify when those prior actions must have been completed; presumably any time before 11 May 2006 qualifies.

There is no indication that this AD has been superseded or cancelled by a later directive as of the source’s publication date. However, in the years since 2006, it is possible that a later AD or an amendment to the maintenance manual has modified the requirements, especially if P/N 46500-7 has itself been superseded by an even newer part. The source predates the present, so we cannot confirm the current status. For a live compliance check, an operator would need to search CASA’s current AD database.

The amendment history provided in the source is minimal: one revision to applicability. No explanatory preamble or reasons for the revision are given beyond the background note that the terminating action part was introduced and production aircraft incorporated it. This sparse documentation is typical of many ADs; the legal effect lies in the current text, not the history.

The source text contains no reference to any litigation. No court case, tribunal decision, or enforcement proceeding is mentioned. This is unsurprising: airworthiness directives are administrative instruments that rarely generate direct litigation. Disputes typically arise in collateral contexts such as contract claims between lessors and lessees, insurance coverage disputes, or personal injury actions following an accident. For example, if an accident occurred due to a landing gear failure, the absence of compliance with this AD could be alleged as negligence per se. However, the source provides no information on any such cases.

We can infer that the original Canadian directive CF-2002-13R2 may have been the subject of regulatory challenge or industry comment during its development, but the Australian AD was issued after that, presumably with those issues resolved. The background states the cause of the failure and the introduction of P/N 46500-5 and then -7, but no legal proceedings are noted.

In Australian civil aviation, operators rarely sue CASA over ADs because the Act allows CASA broad discretion to issue directives without prior consultation, subject only to merits review in the Administrative Appeals Tribunal for decisions that affect a person’s interests. An AD is typically not reviewable until it is enforced, at which point the operator can challenge the enforcement action. There is no reported AAT case specific to AD/DHC-8/119 in publicly available databases as of our knowledge cutoff.

Nevertheless, a thorough compliance analyst would note that the lack of litigation does not mean the directive is risk-free. Operators who challenge an AD in court bear the burden of proving it is unreasonable or unlawful, a high bar. The litigation history of this specific directive is thus a blank slate, but the broader legal framework is well established.

In the United States, the FAA’s AD for the same Bombardier issue may have been challenged, but that is outside the scope of this Australian source. The source only mentions Transport Canada, not the US FAA.

Given the absence of any cited cases, the deepest commentary we can offer is that the directive has apparently been accepted by the industry without court challenge, suggesting the industry found it technically justified and the compliance burden acceptable relative to the safety risk. Alternatively, operators may have chosen to comply rather than face enforcement. Without data, we cannot determine which.

Several details in this AD can trap the unwary operator or compliance officer.

First, the ramp-compliance time for requirement 3 (inspect up-lock roller for low friction liner) is only 30 days from the effective date (11 May 2006, so due by 10 June 2006). That is a very short window for a fleet of aircraft. Operators must schedule this inspection quickly, and if the aircraft is overseas or in heavy maintenance, they must either arrange for a local approved organisation to perform it or fly the aircraft to a suitable base before the deadline. Flying an aircraft that may have the defective roller is itself a risk, though the AD does not prohibit operation before compliance. However, if the operator fails to meet the 30-day deadline, every subsequent flight is a potential violation.

Second, the distinction between part numbers matters. An aircraft may have been delivered with P/N 46500-3 or -5, but the operator might have already replaced one side but not the other. The terminating action requires both sides to be P/N 46500-7. Replacing only one side provides no relief from the inspection regime; both must be done. Operators who replace only the left assembly thinking they are finished will discover during an audit that the right assembly still requires recurrent inspections. Also, if the aircraft has a mix of -3 and -5, the operator must comply with the more stringent requirement: the groove inspection applies only to -5 assemblies, but the roller liner inspection applies to all.

Third, the wear groove measurement must be made to 0.001 inch accuracy. This requires a precision instrument such as a depth gauge or a special tool. The maintenance manual chapter referenced (32-31-21-220-801) presumably provides the correct procedure, but the AD does not specify what tool to use. An inspector using a crude ruler could misread the depth. If the groove depth is exactly 0.007 inches, the assembly must be replaced. If it is 0.0065 inches, it may remain but must be reinspected at the next interval (400 hours/480 cycles). The tolerance is tight; a measurement error of 0.001 inch could mean the difference between a pass and a costly replacement.

Fourth, the up-lock roller free-rotation check (requirement 4(b)) must be performed at the same interval as the groove inspection. The AD says: “If the up-lock roller does not rotate freely, replace the up-lock roller with a roller of the same part number, as per instructions given in Chapter 32-31-21 of the DHC-8 Series 400 Aircraft Maintenance Manual.” Note: it says “same part number”, which is P/N 46575-1. But requirement 3 already required replacing any roller that lacks the low friction liner. So an operator could end up replacing a roller that rotates freely but lacks the liner (requirement 3) or a roller that has the liner but does not rotate freely (requirement 4(b)). The two inspections are separate and both must be satisfied. A roller can have the liner but still be worn or damaged and fail the rotation check.

Fifth, the AFM amendment procedure is detailed and must be followed exactly. The procedure in requirement 1 involves steps 1 through 11, including a caution that if the LDG GEAR INOP caution light illuminates or there is any hydraulic abnormality, the pilot must revert to the alternate extension procedure. The insertion of this procedure does not remove the existing alternate extension procedure; it adds an intermediate step. Operators must ensure that the pages are inserted in the correct location (opposite page 4-21-1) and that the binder or manual is updated.

Sixth, the compliance calculation for “hours air time” and “flight cycles” must be tracked precisely. If an aircraft accumulates 2,500 hours before 3,000 cycles, the due date is the hour threshold. Operators using a calendar-based tracking system could miss the due date if they rely on cycles alone. Similarly for the 400-hour/480-cycle recurring inspection. The AD does not specify what constitutes a flight cycle: typically one takeoff and one landing. But if an aircraft does multiple touch-and-go landings, each counts as a cycle. The operator must have a system to count cycles accurately.

Seventh, the note about “TC AD CF-2002-13R2” may imply that the Canadian directive is the source, but the Australian AD is the legal requirement in Australia. An operator might mistakenly believe they are compliant if they follow the Canadian directive, but if the Australian version has additional requirements (e.g., the revision to applicability), they could be non-compliant. Always use the local AD.

Eighth, the terminating action is not truly “terminating” if a subsequent AD appears. The AD itself says the terminating action ends the requirements of this AD only. A future AD could require further modifications to the same assembly or to other parts. Operators should not assume that installing P/N 46500-7 provides permanent relief from all landing gear ADs.

Compliance with AD/DHC-8/119 requires a systematic, documented approach. The following step-by-step plan assumes the operator has identified their aircraft as falling within the applicability (Models 400, 401, 402, serial numbers 4001 and 4003 through 4087, fitted with P/N 46500-3 or 46500-5 up-lock assemblies). If the aircraft already has P/N 46500-7 from the factory, the applicability clause excludes it, but the operator should verify by checking the aircraft’s modification status and part number records.

Step 1: Immediate actions (within 30 days of 11 May 2006).

• Amend the Aircraft Flight Manual (AFM) PSM 1-84-1A by inserting the abnormal procedure on the page opposite 4-21-1 as specified in Requirement 1(a). This can be a copy of the AD itself. Record the revision in the AFM log. Notify all flight crews in writing, such as through a bulletin or directive file. Retain evidence of notification.
• Inspect both the left and right main landing gear up-lock rollers for the presence of an inner low-friction liner, following Bombardier Alert Service Bulletin A84 32-15 (dated 4 February 2002 or later TC-approved revision). If the liner is absent on either side, replace the roller with a new P/N 46575-1 roller per Chapter 32-31-21 of the maintenance manual. Record the inspection results and any part replacement in the aircraft technical log.

Step 2: Replacement of up-lock assemblies (initial compliance).

• Determine the current accumulated hours and flight cycles on each up-lock assembly (P/N 46500-3 or -5). If the assembly has already exceeded 2,500 hours or 3,000 cycles, replacement is due immediately. Otherwise, schedule replacement before reaching that threshold. The replacement may use new or overhauled P/N 46500-3, -5, or -7. However, given that P/N 46500-3 is out of production and P/N 46500-5 imposes a more frequent inspection regime, the most cost-effective choice is to replace with the terminating part P/N 46500-7. Perform replacement per Chapter 32-31-21 instructions. After replacement, update the maintenance records with the new part numbers and the date/time/cycles.

Step 3: Recurrent inspections for aircraft still on P/N 46500-5.

• If the aircraft still has P/N 46500-5 assemblies (i.e., the operator has not yet replaced them with -7), then before the assembly reaches 2,500 hours/3,000 cycles and thereafter every 400 hours or 480 flight cycles (whichever occurs first), perform two inspections:
  • (a) Inspect the surface of the up-lock latch lower jaw for a wear groove. Measure the groove depth to 0.001 inch accuracy using the procedure in Task 32-31-21-220-801. If depth exceeds 0.007 inches, replace the assembly with P/N 46500-7.
  • (b) Inspect the up-lock roller P/N 46575-1 for free rotation. If it does not rotate freely, replace the roller with a new P/N 46575-1 per Chapter 32-31-21.
• Record each inspection in the aircraft log with the date, hours, cycles, and measurements. If a replacement is performed, note the new part number and reset the compliance interval for that assembly.

Step 4: Terminating action.

• Replace both left and right up-lock assemblies with P/N 46500-7. Once this is accomplished, you may remove the AFM procedure inserted in Step 1 from the flight manual (per Requirement 1(b)). However, ensure that all flight crews are advised of the removal. The directive’s note says “advise all flight crews of this change.” Then mark the AD as fully complied and terminated in the aircraft’s AD compliance status record. No further inspections under this AD are required.

Step 5: Documentation and tracking.

• Maintain a log of each AD requirement with dates of accomplishment. For the recurring inspections on P/N 46500-5, set up a tracking system based on both hours and cycles, alerting the maintenance team before the next due date. Because the interval is relatively short (400 hours/480 cycles), the system must be accurate. Use a computerised maintenance management system if available.

Step 6: Cross-check with other directives.

• Verify that the aircraft’s compliance with TC AD CF-2002-13R2 is complete if the aircraft is also subject to Canadian regulations. Ensure that any differences between the two directives are resolved in favour of the more stringent requirement. For Australian operations, the CASA AD is the binding instrument.

Step 7: Audit readiness.

• Keep copies of the AD, the service bulletin, the maintenance manual task pages, and all records of inspections, measurements, and part replacements. These documents may be requested during a CASA audit or by a lessor or purchaser. The records should clearly show that the 30-day deadline was met and that the recurring inspections are current.

Operators who follow this plan will satisfy the legal requirements and reduce the risk of landing gear malfunction. Those who delay or ignore the AD expose themselves to enforcement and safety hazards.