AD/DHC-1/28 Amdt 10 - Undercarriage Mounting Casting

The AD rests on a short set of technical and regulatory concepts expressed in its text. First, the safety hazard targeted is cracking in the undercarriage mounting casting: "Numerous cases of cracking have been documented in the main undercarriage leg mounting casting in each wing" (Background). The AD explains the mechanism relevant to inspection policy: the cracks arise from "stress corrosion which is related primarily to elapsed calendar time rather than flight hours" (Background). That mechanistic statement matters for inspection frequency design because time-based deterioration implies that aircraft with low utilisation nonetheless accrue risk.

Second, the AD does not itself specify inspection technique or intervals; instead it delegates the substantive inspection methodology and the interval and limit parameters to a separate technical document, "British Aerospace Technical News Sheet CT (C1) No. 165 Issue 7, dated 1 June 2010 or later revision approved by the UK CAA" (Requirement). The AD thus operates as a regulatory pointer: compliance requires adherence to that external technical publication as approved by the UK CAA. The AD further notes that "Wings modified in accordance with De Havilland Mod H.310 may not need further inspection per this AD" and tells operators to consult the requirement document and the TC holder for confirmation (Requirement).

Third, the AD records a history of incremental revisions to the underlying requirement: amendments previously "relaxed inspection intervals, and introduced suggested examination techniques" and later amendments "reflected a variation to re-inspection intervals", "amended the mounting casting top and bottom flange inspection limits", "corrected administrative problems", introduced a requirement to defuel prior to inspection, and updated the requirement document to Issue 7 (Background). Amendment 10, the instrument in hand, does not alter inspection mechanics or intervals; it adds the Portuguese-manufactured T Mk 20 to applicability (Background).

Fourth, the AD exhibits cross-jurisdictional referencing. It requires adherence to a British Aerospace technical publication and the approval of any later revision by the UK CAA, and it explicitly refers to a UK CAA AD ("UK CAA AD 2807 refers") (Requirement; Note). The AD was issued by the Australian regulator's delegate, showing that CASA is importing or aligning an Australian AD with UK-origin technical material and regulatory references (signature and Requirement).

Finally, the AD contains a compliance grandfathering statement: "Prior compliance with this Directive at Amendment 8 constitutes compliance with this amendment" (Compliance). This recognises earlier work done by operators under a previous amendment as satisfying the present requirement, thereby reducing redundant work for aircraft already inspected under Amendment 8.

The AD identifies the affected population by production origin and model: "English production (C1), all models, and Portuguese (T Mk 20) production models" (Applicability). Practically, that means:

• Aircraft owners and operators of De Havilland DHC-1 (Chipmunk) airframes whose production origin is English (C1) , all model variants , are within the AD's applicability and must comply with the inspection requirement specified in the referenced technical news sheet (Applicability; Requirement).

• Aircraft owners and operators of the Portuguese-produced T Mk 20 model are newly included by this Amendment and therefore become subject to the same inspection requirements (Background; Applicability).

• Maintenance organisations and licensed maintenance personnel who carry out inspections and defect rectification for these aircraft are implicated because the AD requires inspections "in accordance with" the Technical News Sheet; those organisations must follow that document's procedures and the interval/limit specifications (Requirement; Compliance).

• The type certificate holder (the TC holder) is a named point of contact in the AD; the text instructs operators to "contact the TC holder for further information if there is any doubt about your aircrafts status in relation to this modification and the need for continuing inspections" (Requirement). That assigns the TC holder a role in clarifying modification status and inspection necessity.

• The UK Civil Aviation Authority appears as an approving body for any later revisions of the Technical News Sheet, since the AD requires use of Issue 7 "or later revision approved by the UK CAA" (Requirement). That points to a cross-jurisdictional regulatory dependence where UK CAA approval governs which later revisions can be relied upon for compliance.

• The Civil Aviation Safety Authority in Australia is the issuing regulator, represented by its delegate Glen Steemson; the AD is an instrument of CASA with an effective date in Australia and a signature from the delegate (signature block; Compliance).

Note that the AD signals that certain modified wings "may not need further inspection" if altered in accordance with De Havilland Mod H.310 (Requirement). Aircraft owners whose airframes have that modification must verify whether their modification status removes the inspection obligation. The AD instructs them to consult the requirement document and the TC holder for that confirmation.

The AD does not list any exemptions other than the modification-related conditional relief, and it does not assign duties to entities outside those groups. The compliance instruction that "Prior compliance with this Directive at Amendment 8 constitutes compliance with this amendment" affects owners/operators who already complied under Amendment 8 by removing the need for repeat inspection work specifically for the purpose of meeting Amendment 10 (Compliance).

The document sets a concise set of duties, and a small number of rights or clarifying provisions that reduce duplication of effort:

Duties

• Perform inspections in accordance with British Aerospace Technical News Sheet CT (C1) No. 165 Issue 7, dated 1 June 2010, or a later revision that is approved by the UK CAA (Requirement). The AD makes adherence to the specified external technical document the core duty.

• Meet the inspection intervals and limits as specified in the Requirement document (Compliance). The AD expressly delegates interval setting to that technical publication rather than specifying them in the AD text.

• If there is doubt about whether a wing modification (De Havilland Mod H.310) removes the need for continuing inspections, consult the requirement document and contact the TC holder for clarification (Requirement). This imposes an informational duty on the operator to resolve uncertainty with the TC holder.

• Observe any preparatory actions recorded in earlier amendments to the Requirement document. For example, Amendment 8's introduction of a need to "defuel the aircraft prior to the inspection" is mentioned in the background as a prior change to the Requirement document and therefore may be relevant to current inspections (Background).

Rights, clarifications and limiting rules

• Wings modified by De Havilland Mod H.310 "may not need further inspection per this AD" (Requirement). This creates a limited right to avoid recurring inspections if the modification status is confirmed, but the AD conditions this on consultation with the Requirement document and the TC holder.

• Prior compliance under Amendment 8 is accepted as compliance with this Amendment: "Prior compliance with this Directive at Amendment 8 constitutes compliance with this amendment" (Compliance). That recognises prior work and prevents double compliance where the same inspections were conducted under the earlier amendment.

• The AD permits use of later revisions of the Technical News Sheet, but only where those later revisions are "approved by the UK CAA" (Requirement). This provides operators leeway to use updated technical guidance, subject to UK CAA approval rather than unilateral adoption.

Delegation and decision points

• The AD delegates detailed inspection content, intervals and limits to the specified Technical News Sheet and to further UK CAA approvals (Requirement). The operator's decisions therefore centre on obtaining the approved version of the technical sheet, determining whether the aircraft has Mod H.310, and arranging inspection intervals and practices in line with the technical material.

• The issuing authority for this AD in Australia is the Civil Aviation Safety Authority, evidenced by the signature block, which may be relevant for any administrative questions about the instrument itself (signature block; Compliance).

The AD does not specify remedial standards for cracked parts, repair methods, or airworthiness restoration limits within its text. Those technical remediation details are left to the Requirement document referenced.

The text of this AD does not set out penalties, sanctioning mechanisms, or specific enforcement procedures. The instrument comprises an operational requirement , to inspect in accordance with the named Technical News Sheet and to repeat inspections as specified there , and records administrative details such as effective date and applicability (Requirement; Compliance). The AD is signed by "Glen Steemson, Delegate of the Civil Aviation Safety Authority" and dated 17 June 2011, with an effective date of 23 June 2011 (signature block; Compliance). The presence of the delegate's signature identifies the issuing authority but the AD text itself contains no express penalty provisions.

Because the AD references external technical material for inspection intervals, techniques and limits, enforcement or sanctioning would necessarily hinge on how compliance with the AD is assessed against that external document; however, the AD does not describe the monitoring, reporting or audit mechanism within its text. The AD does record an internal compliance concession: "Prior compliance with this Directive at Amendment 8 constitutes compliance with this amendment" (Compliance), which reduces the likelihood of enforcement action where earlier compliance can be demonstrated.

The AD also cross-refers to UK regulatory material by requiring Technical News Sheet revisions to be "approved by the UK CAA" and by making reference to "UK CAA AD 2807" (Requirement; Note). Those cross-references do not themselves prescribe Australian enforcement practice but they identify which external documents constitute the standard for measuring compliance.

If an operator needs to resolve whether a previously applied modification (De Havilland Mod H.310) obviates the need for further inspections, the AD directs the operator to consult the Requirement document and the TC holder (Requirement). That procedural direction functions as a compliance verification step, but the AD does not assign a formal role to the TC holder in enforcement.

In sum, the AD prescribes inspection duties and identifies authoritative documents and contacts, but it does not in its text specify penalties, enforcement mechanisms, inspection reporting requirements, or administrative sanctions. Any such enforcement regime or penalties would have to be found in the broader statutory framework under which CASA issues ADs, or in secondary administrative procedures, which are not reproduced in this AD text.

The AD explicitly interfaces with specific non-Australian regulatory and technical instruments. It directs compliance with "British Aerospace Technical News Sheet CT (C1) No. 165 Issue 7, dated 1 June 2010 or later revision approved by the UK CAA" and notes "UK CAA AD 2807 refers" (Requirement; Note). Those references create the following concrete interactions:

• Cross-reference to UK technical standards: The AD requires adherence to a British Aerospace Technical News Sheet as the operative technical standard for inspection methods, intervals and limits. It further conditions the use of any later revision of that document on approval by the UK Civil Aviation Authority. Therefore, the AD imports the UK document as the Australian operational standard for the specific safety issue identified.

• Cross-reference to UK regulatory approvals: By requiring UK CAA approval of later revisions, the AD puts the UK CAA in the role of gatekeeper for which updated technical guidance can be relied on for compliance in Australia. This is a cross-jurisdictional dependency on UK administrative approval.

• Interaction with type certificate holder responsibilities: The AD instructs operators to "contact the TC holder for further information if there is any doubt about your aircrafts status in relation to this modification and the need for continuing inspections" (Requirement). That places the TC holder in a practical role for clarification, although the AD does not specify any statutory obligation of the TC holder beyond being a point of reference.

• Relationship to prior AD amendments: The AD explicitly folds in prior compliance by stating "Prior compliance with this Directive at Amendment 8 constitutes compliance with this amendment" (Compliance). Internally, the AD therefore interacts with its own amendment history in a way that prevents duplication of regulatory labour where prior compliance has already been achieved.

• Reference to preparatory measures included in prior amendments: The background notes that Amendment 8 "reflects the need to defuel the aircraft prior to the inspection" and other past amendments modified inspection intervals, limits and techniques (Background). Those prior changes, incorporated into the Requirement document historically, continue to be relevant to current compliance practice.

What the AD does not do in its text is expressly reference Australian aviation statutes, regulations, or the mechanisms by which CASA enforces compliance (for example, reporting obligations, certification actions, or penalties). It also does not reference airworthiness directives from regulators other than the UK CAA. The practical result is that the AD imports UK technical material as the operative standard for this safety problem and relies on UK CAA approvals to validate later revisions, while leaving unspecified in the AD the Australian administrative enforcement processes that ensure adherence to these requirements.

The instrument contains a short amendment history embedded in the Background section that summarises the evolution of the underlying inspection requirement and shows how the current Amendment 10 fits into that history. The AD states that "This Amendment becomes effective on 23 June 2011" and that "This amendment adds the Portuguese manufactured DHC-1 (T Mk 20) to the applicability of this AD" while also recording "There is no change to the requirements or compliance from the previous amendment" (Compliance; Background).

The more detailed recent amendment history contained in the AD records:

• Amendment 4: "relaxed inspection intervals, and introduced suggested examination techniques." That indicates a previous move to reduce inspection frequency and to provide suggested techniques for examinations, pointing to an iterative calibration of inspection burden and detection capability (Background).

• Amendment 5: effective 23 May 1996, "reflected a variation to re-inspection intervals." This further indicates adjustment of re-inspection timing (Background).

• Amendment 6: effective 7 October 1999, "amended the mounting casting top and bottom flange inspection limits." This shows a refinement of where on the mounting casting inspections should focus and what limits govern acceptable condition (Background).

• Amendment 7: effective 2 December 1999, "corrected administrative problems which occurred during processing of Amendment 6." This was an administrative correction rather than a technical change (Background).

• Amendment 8: "was issued in response to the latest issue of the Requirement document which reflects the need to defuel the aircraft prior to the inspection." This indicates a safety or practical change to inspection preconditions requiring aircraft defuelling (Background).

• Amendment 9: effective 10 January 2011, "was issued to update the requirement document to Issue 7." That updates the reference Technical News Sheet to Issue 7, dated 1 June 2010 (Background; Requirement).

• The original issue of the Airworthiness Directive became effective on 1 April 1979. This indicates the AD lineage extends back multiple decades (Background).

Amendment 10, the current text, adds applicability to Portuguese manufactured T Mk 20 models and leaves inspection requirements and compliance unchanged compared with Amendment 9 (Background). The AD further records that "Prior compliance with this Directive at Amendment 8 constitutes compliance with this amendment" which is an internal administrative continuity provision (Compliance).

Together the amendment history in the AD documents the regulator's iterative adjustments to inspection scope, intervals and administrative practices, and the current amendment is limited in scope to expansion of applicability. The AD does not provide the text of earlier amendments or the specific technical modifications made to the Requirement document; those details are in the external Technical News Sheet and related UK CAA materials that the AD imports by reference.

The AD as provided contains no litigation history and cites no judicial or administrative tribunal decisions. The text is administrative and evidences an executive agency action: it sets an inspection requirement, records technical background, and identifies amendment history (Requirement; Background; Compliance). No cases or disputes are mentioned.

Because the instrument does not include any description of enforcement actions, penalties, or dispute-resolution mechanisms within its text, there are no litigation references for this particular AD in the source material. The background and amendment history recount changes to inspection intervals, techniques and administrative corrections, but those are recorded as regulatory updates rather than as outcomes of litigated disputes (Background).

Practitioners should note from the AD that administrative questions and technical uncertainties are to be directed to the TC holder and that the AD imports UK CAA approvals for later revisions of the technical guidance (Requirement). If compliance disputes or enforcement actions were to arise in practice, they would likely involve interpretation of compliance against the referenced Technical News Sheet and the question of whether a wing modification such as De Havilland Mod H.310 removes the inspection obligation, but the AD does not report any such litigation or adjudication.

In the absence of litigation material in the AD text, the AD serves as a primary source of regulatory obligation and technical reference. Any subsequent court or tribunal history relevant to disputes about this AD would have to be sought outside the AD text itself.

The AD contains several operational details and conditional elements that can catch operators, maintenance organisations, or compliance officers if they are overlooked. The following are the principal "gotchas" drawn from the AD text and the amendment history:

• Calendar-time degradation: The AD states that cracking is "related primarily to elapsed calendar time rather than flight hours" (Background). If an operator assumes low flight hours mean low risk, that assumption would be incorrect. The inspection policy is intended to respond to time-dependent stress corrosion, so aircraft that sit idle can still require inspection.

• Applicability expansion: Amendment 10 "adds the Portuguese manufactured DHC-1 (T Mk 20) to the applicability of this AD" (Background). Operators of Portuguese-manufactured T Mk 20 airframes who previously did not consider themselves subject to the AD may be unaware they now fall within its scope.

• Delegation of substantive detail to an external document: The AD does not specify inspection techniques, interval values, or acceptance limits in its text; it orders inspection "in accordance with British Aerospace Technical News Sheet CT (C1) No. 165 Issue 7" and any later revision "approved by the UK CAA" (Requirement). A gotcha is failing to obtain and follow the latest approved revision of that Technical News Sheet, or to rely on an unapproved revision.

• Conditional exemption via Mod H.310: The AD states that wings modified by De Havilland Mod H.310 "may not need further inspection per this AD" (Requirement). That is a conditional relief, not an automatic exemption. Operators must confirm whether the specific modification on their aircraft achieves the relevant mitigation, and the AD directs them to consult the Requirement document and contact the TC holder. Failing to confirm modification coverage could result in missed inspections or unnecessary inspections.

• Defuelling prior to inspection: The AD's amendment history records that Amendment 8 "reflects the need to defuel the aircraft prior to the inspection" (Background). If the current Issue 7 of the Technical News Sheet still requires defuelling (as indicated in prior amendments), operators must plan for fuel management and associated logistics before inspections.

• Reliance on UK CAA approvals: Later revisions of the Technical News Sheet are permitted only if "approved by the UK CAA" (Requirement). Operators who adopt an update without UK CAA approval may not be following the AD's permitted pathway for updated technical guidance.

• Prior compliance credit: The AD states "Prior compliance with this Directive at Amendment 8 constitutes compliance with this amendment" (Compliance). Operators who did work under Amendment 8 must retain evidence of that compliance. Failing to document prior inspections could lead to unnecessary repetition or administrative questions.

• No penalties or enforcement text in the AD: The absence of penalty language in the AD may lead to uncertainty about reporting and enforcement procedures. The AD does not specify reporting, audits, or notification obligations; operators should not assume that no administrative steps are required. They must follow the Requirement document and any CASA processes external to the AD text.

• Administrative corrections in past amendments: The AD records that Amendment 7 "corrected administrative problems which occurred during processing of Amendment 6" (Background). That history indicates that administrative processing of amendments has produced errors before; practitioners should ensure they are referencing the correct amendment and Issue number.

• Cross-jurisdictional documentation management: Because the AD depends on UK-origin materials and UK CAA approvals, the administrative burden may include obtaining imported documents and verifying their approval status with the UK CAA. That can complicate compliance logistics for Australian-based operators.

Operators and maintainers should treat each of these items as an operational checklist point: verify production origin, check for Mod H.310 and confirm by TC holder, obtain and follow the approved Technical News Sheet Issue 7 or later UK CAA-approved revision, plan for defuelling if required, and retain records showing prior compliance if relying on Amendment 8 credit.

The AD's compliance pathway is straightforward but depends on an external technical document. The following steps, stated in terms that map directly to the AD text, will make compliance practical and documentable:

1. Identify whether the airframe is covered by the AD. Confirm the production origin and model: "English production (C1), all models, and Portuguese (T Mk 20) production models" are applicable (Applicability). If the aircraft is a C1 English production or a Portuguese T Mk 20, proceed to step 2.

2. Determine modification status. Check whether the wings have been modified in accordance with De Havilland Mod H.310. If so, review Mod H.310 documentation and proceed to step 3 to confirm whether the modification removes the need for further inspections. The AD states that such wings "may not need further inspection per this AD" but requires confirmation via the Requirement document and the TC holder (Requirement).

3. Obtain the required Technical News Sheet. Acquire "British Aerospace Technical News Sheet CT (C1) No. 165 Issue 7, dated 1 June 2010" or any later revision only if that revision has been "approved by the UK CAA" (Requirement). Use the latest UK CAA-approved revision for inspection procedure, intervals and acceptance limits.

4. Confirm preparatory actions. Check the Requirement document (and the amendment history) for any preconditions such as defuelling. The AD's amendment history notes that Amendment 8 "reflects the need to defuel the aircraft prior to the inspection" (Background). If Issue 7 or a later approved revision requires defuelling, arrange safe defuelling and associated procedures before inspection.

5. Conduct inspections per the Requirement document. Perform the inspection techniques, intervals and limit checks exactly as specified in the Technical News Sheet CT (C1) No. 165 Issue 7 or the later UK CAA-approved revision. The AD expressly defers to that document for interval and limit specification: "At the inspection intervals and limits specified in the Requirement document" (Compliance).

6. Consult the TC holder for uncertainty. If there is any doubt "about your aircrafts status in relation to this modification and the need for continuing inspections" contact the TC holder for clarification (Requirement). Document any correspondence and determinations from the TC holder as evidence underpinning compliance decisions.

7. Record compliance and prior credit. If the inspections were already carried out under Amendment 8, retain documentation demonstrating that compliance because the AD states "Prior compliance with this Directive at Amendment 8 constitutes compliance with this amendment" (Compliance). Keep inspection reports, dates, and sign-offs available for audit or inquiries.

8. Verify effective dates. The AD "becomes effective on 23 June 2011" (Compliance). Ensure inspections are scheduled or have been completed in line with the effective date and the intervals specified in the Requirement document.

9. Manage documentation for cross-jurisdictional approvals. Where later revisions to the Technical News Sheet are to be used, obtain evidence of UK CAA approval for the specific revision relied upon. File that approval documentation with your maintenance record substantiating the use of that revision for compliance.

10. Maintain audit trail. Because the AD does not specify reporting steps in its text, maintain a clear audit trail of the following items: aircraft model and production origin, Mod H.310 status and verification, Technical News Sheet issue used and proof of UK CAA approval if required, date and results of inspection, any remedial work performed, and any TC holder correspondence relied upon.

Following these steps aligns the operator with the obligations and clarifications the AD explicitly provides. Where the AD instructs consultation with the TC holder, treat that consultation as a compliance step and make a record. The AD's simplicity means the key compliance risk is administrative: using the correct issue of the Technical News Sheet, obtaining UK CAA approval for later revisions, and retaining proof of prior compliance where applicable.