AD/DHC-1/22 Amdt 4 - Tailplane Structure

The AD rests on a compact set of technical and administrative concepts, each specified in the printed text.

• Applicability and exclusion. The AD applies to "All English production (C1) all models and Portuguese production (T Mk 20) aircraft which have not been modified in accordance with a scheme approved by the authority (locally developed reinforcement kit)" (Applicability). This sets a binary scope based on production origin and modification status. The exclusion for aircraft modified under an approved reinforcement scheme is explicit.

• Mandated inspection method. The AD requires inspection "in accordance with British Aerospace TNS CT(C1) No. 157, Issue 3, dated 28 May 1986" (Requirement). The identified inspection is radiographic and targets the tailplane upper and lower spar flanges at the fuselage attachment brackets (Background). The AD thereby incorporates an external technical standard by reference.

• Recurrence interval tied to Role Factor. The AD sets repeat inspections "of paragraph 8 of the TNS" at intervals not exceeding six years from initial compliance, but shortens the maximum interval to three years for aircraft operated on a Role Factor of 4 "see TNS CT(C1) No. 138 Issue 5" (Compliance). The Role Factor concept is taken from the TNS material and is used to differentiate inspection periodicity by operational use.

• Effective date and authority. The instrument's operative date is 22 June 2011 and it is issued by a CASA delegate, Glen Steemson, dated 16 June 2011 (Compliance; signature block). The AD is presented as Amendment 4 to an existing AD (AD/DHC-1/22), with an amendment history recited in the Background.

• Linkage to other documents and prior ADs. The AD references related TNS and AD instruments: TNS No. 138 Issue 5 (subject of UK CAA AD 2804 PRE 80 and CASA AD/DHC-1/12 Amendment 6) and historical amendments to AD/DHC-1/22 including Amendments 1-3 with respective effective dates and changes (Background).

• Radiographic inspection focus. The Background identifies the specific structural area of concern as "the tailplane upper and lower spar flanges at the fuselage attachment brackets" and explains that Amendment 3 established repetitive radiographic inspections for those elements; Amendment 4 extends applicability (Background).

These concepts function together: a targeted structural inspection regime, mandated by reference to a technical note, with recurrence intervals differentiated by operational Role Factor, and an exclusion for aircraft modified pursuant to an approved reinforcement scheme.

The AD identifies the affected population narrowly and includes a clear exclusion.

Primary affected parties

• Owners/operators of De Havilland DHC-1 (Chipmunk) series aeroplanes produced in England (C1 production models) and those Portuguese-produced aircraft of the T Mk 20 variant, except where excluded by modification approval (Applicability). That group is the set of aircraft to which the inspection requirement applies.

Secondary affected parties

• Maintenance providers responsible for carrying out radiographic inspections in accordance with British Aerospace TNS CT(C1) No. 157 Issue 3 (Requirement; Background). These providers must have capability to perform radiographic inspection of the specified tailplane spar flanges to the referenced standard.

• Technical authorities and documentation holders. The AD incorporates British Aerospace TNS CT(C1) No. 157 Issue 3 (Requirement) and references TNS CT(C1) No. 138 Issue 5 (Compliance/Background). Operators and maintainers must obtain and follow those TNS documents for procedural detail; the documents determine what "paragraph 8" contains and how Role Factors are assigned.

Particular exclusions

• Aircraft modified "in accordance with a scheme approved by the authority (locally developed reinforcement kit)" are excluded from the requirement (Applicability; Background). The AD notes that "some aircraft have been modified to incorporate a locally developed reinforcement kit, so as to be excluded from this AD" (Background). That creates a clear status distinction: an aircraft’s modification record determines whether it is within the AD’s scope.

Decision-makers and record-keepers

• The authority (CASA) is the issuer. The exclusion is expressed as modification "approved by the authority," which means a CASA-approved modification scheme determines exclusion eligibility (Applicability). The AD is signed by a CASA delegate (Glen Steemson), indicating the issuing authority and date (signature block).

Practical implications for users

• Operators must determine whether their aircraft are English production C1 models or Portuguese T Mk 20s and whether they have been modified under an approved reinforcement scheme. If in scope, they must arrange an initial radiographic inspection as mandated and schedule repeats according to paragraph 8 of the TNS at intervals not exceeding six or three years depending on Role Factor (Requirement; Compliance).

The text does not list additional groups such as regulators beyond CASA, insurers, or third-party owners, nor does it specify certification or record-keeping procedures beyond the requirement to carry out inspections in accordance with the referenced TNS.

Duties imposed by the AD are specific and procedural; rights or remedies are not set out in the text.

Primary duties

• Conduct the mandated inspection: Operators of applicable aircraft must "Inspect the tailplane upper and lower spar flanges in accordance with British Aerospace TNS CT(C1) No. 157, Issue 3, dated 28 May 1986" (Requirement). The inspection method is radiographic, aimed at the spar flanges at the fuselage attachment brackets (Background).

• Repeat inspections at prescribed intervals: From the date of compliance with the initial inspection, repeat the inspections of paragraph 8 of the TNS at intervals not exceeding six years, except where the aircraft is operated on a Role Factor of 4, in which case the inspection interval shall not exceed three years (Compliance).

• Determine and apply Role Factor: Operators whose aircraft are operated on Role Factor 4 must adhere to the shorter three-year inspection interval; the AD points to TNS CT(C1) No. 138 Issue 5 for Role Factor guidance (Compliance). Operators therefore have the duty to classify operational role consistent with the TNS.

Conditions and exclusions

• Exclude modified aircraft: Aircraft modified "in accordance with a scheme approved by the authority (locally developed reinforcement kit)" are not subject to the inspection requirement (Applicability; Background). The duty to inspect is thereby conditional on modification status.

Administrative duties implicit in the AD

• Obtain and follow the referenced TNS documents. The AD requires compliance "in accordance with" a named TNS; meeting that duty requires access to and application of the technical procedures contained in those documents (Requirement).

Rights and remedies

• The AD text does not state rights, appeals procedures, or remedies for affected parties within its body. It does not set out any mechanism for seeking relief from the inspection requirement, alternative compliance methods, or waivers. It does, however, record that modified aircraft approved by the authority are excluded,functioning as an explicit form of relief for aircraft that have undergone an approved reinforcement modification (Applicability; Background).

Operational discretion left to parties

• The AD specifies the technical standard and intervals but not the detailed logistics of inspection scheduling, contracting maintenance providers, or methods for documenting compliance. These operational matters are therefore delegated to operators and maintainers subject to the single constraint of following the referenced TNS.

In short, the AD establishes three concrete duties: conduct the TNS CT(C1) No. 157 radiographic inspection of the tailplane spar flanges; repeat at specified maximum intervals based on paragraph 8 and Role Factor; and confirm applicability (i.e., whether an approved reinforcement kit excludes the aircraft). The AD does not enumerate rights, appeals, or alternative compliance pathways within the text provided.

The text of AD/DHC-1/22 Amdt 4 does not itself specify penalties, sanctions, or enforcement procedures. The document records the directive, sets an effective date of 22 June 2011, and is signed by a CASA delegate (Glen Steemson, 16 June 2011), but it contains no express penalty provisions, fines, or procedural enforcement steps within the printed AD text.

What the AD does record that bears on enforcement

• Mandatory requirement language. The AD prescribes inspection obligations in mandatory terms: "Inspect ... in accordance with British Aerospace TNS CT(C1) No. 157" and commands repeat inspections at specified maximum intervals (Requirement; Compliance). The use of mandatory phrasing indicates the AD is an operative instrument that creates obligations for applicable aircraft.

• Authority approval for modification-based exclusion. The exclusion for aircraft "modified in accordance with a scheme approved by the authority (locally developed reinforcement kit)" ties an exemption to a formal approval process by the authority (Applicability). That implies that whether an aircraft is excluded depends on a recorded approval decision by the issuing authority.

What the AD does not state

• It does not spell out what consequences flow from non-compliance with the inspection requirement, nor does it detail how compliance is to be demonstrated or recorded. The AD does not name an enforcement agency beyond the issuing authority, nor does it identify penalties, certificate actions, or timelines for rectification of non-compliance.

Implications for readers based solely on the AD text

• The AD imposes clear obligations but leaves unspecified any sanctioning regime in the printed instrument. Parties notified must therefore treat the inspection requirements as mandatory but cannot, on the basis of this text alone, point to prescribed penalties or enforcement mechanisms inside the AD itself.

Users requiring certainty about sanctions or enforcement procedures will need to consult the issuing authority for authoritative information about enforcement practice and any separate regulatory instruments that define penalties, record-keeping, or compliance verification. The AD does reference related ADs and TNS documents but does not provide cross-referenced penalty content in the printed amendment text.

The amendment text itself provides limited, specific cross-references to technical notes and other ADs; it does not purport to amend or displace broader statutory texts or to define interactions with other legislation. The AD directs readers to and relies on the content of technical notes and prior ADs in the following ways.

Referenced technical material and ADs

• British Aerospace TNS CT(C1) No. 157 Issue 3 (dated 28 May 1986) is incorporated by reference for the inspection method (Requirement). The AD therefore depends on that TNS for procedural detail and effectively makes the TNS operative for the purposes of compliance with this directive.

• TNS CT(C1) No. 138 Issue 5 is referenced in relation to Role Factor and is noted as "the subject of UK CAA AD 2804 PRE 80 and CASA AD/DHC-1/12 Amendment 6" (Requirement; Background). That linkage indicates that paragraph 8 of TNS and Role Factor definitions are not standalone but are part of a family of technical materials and prior ADs.

• The AD is Amendment 4 to AD/DHC-1/22. The Background lists Amendment 1 (effective 30 November 1985), Amendment 2 (effective 13 July 2000), and Amendment 3 (effective 23 October 2008), and summarises the subject matter of past amendments (Background). Thus, this instrument is one element in an evolving AD regime for this airframe type.

Nature of the interaction as stated in the text

• The AD integrates external technical material by reference rather than reproducing all technical detail. Compliance requires adherence to those external instruments; therefore, satisfying this AD is operationally dependent on cross-document consistency (Requirement; Compliance).

• The text indicates that TNS No. 138 Issue 5 is the subject of other ADs (UK CAA AD 2804 PRE 80 and CASA AD/DHC-1/12 Amendment 6), showing cross-jurisdictional coordination on inspection standards for related issues (Background).

Limits of the AD’s stated interactions

• The AD does not identify any conflict resolution mechanism among the referenced documents, nor does it say how to resolve discrepancies between the TNS and other ADs; it simply instructs compliance "in accordance with" the named TNS and cites related materials. The AD does not mention other civil aviation legislation, regulatory penalties, certification doctrine, or how compliance affects airworthiness certificates within the scope of the text provided.

Practitioner note based on the AD’s text

• Operators and maintainers must treat the named TNS and the family of related ADs as the operative procedural corpus for carrying out the inspections required by this AD. Any questions about how this AD aligns with other regulatory instruments or about enforcement should be referred to the issuing authority, as the AD itself does not set out those interactions beyond naming related documents.

The AD contains a concise amendment history in the Background section. The current instrument is Amendment 4, effective 22 June 2011, and the Background summarises previous amendments and what they changed.

Chronology and substance as given in the AD

• Initial issue (implied): The AD traces back to an initial issue which led to inspections being required, but the AD text explicitly records subsequent amendments rather than the very first promulgation date.

• Amendment 1, effective 30 November 1985: Introduced a radiographic inspection of the tailplane front spar joints and required a repeat of the inspections carried out in accordance with the initial issue of the AD (Background).

• Amendment 2, effective 13 July 2000: Excluded modified aircraft from the requirement. Specifically, this amendment recognised that some aircraft had been modified so as to be excluded from the inspection requirement (Background).

• Amendment 3, effective 23 October 2008: Required repetitive radiographic inspections of the upper and lower spar flanges at the fuselage attachment brackets. It also updated the TNS reference. The Background notes that "No additional work was required as a result of this amendment",meaning Amendment 3 formalised repetitive inspection but did not alter the substantive work required where it was already being done (Background).

• Amendment 4 (this instrument), effective 22 June 2011: Adds the Portuguese manufactured T Mk 20 to the applicability of this Airworthiness Directive. The Background explains that a review indicated the inspection is also applicable to this model (Background). The current AD therefore expands the scope of aircraft covered by the prior inspection regime.

Other details recorded in the Background

• The Background emphasises that "some aircraft have been modified to incorporate a locally developed reinforcement kit, so as to be excluded from this AD." That thread recurs across amendments 2-4 and explains the continuing relevance of approved modifications as a basis for exclusion (Background).

• The TNS references have been updated over time; Amendment 3 updated the TNS reference and required repetitive radiographic inspections of the upper and lower spar flanges at the fuselage attachment brackets (Background). The current AD cites British Aerospace TNS CT(C1) No. 157 Issue 3 (Requirement) and notes TNS No. 138 Issue 5 is the subject of other ADs (Requirement; Background).

Form and signatory

• The AD is recorded as issued by a CASA delegate, Glen Steemson, on 16 June 2011, with an effective date of 22 June 2011 (signature block; Compliance). The AD label shows "AD/DHC-1/22 Amdt 4" and the date line "13/2011" consistent with the amendment numbering.

The amendment history in the AD text therefore provides a confined but clear trail: initial inspections and repeat obligations established earlier, recognition and formalisation of exclusion for approved reinforcement modifications, the addition of repetitive inspections for particular spar flanges in 2008, and the expansion of applicability to Portuguese-built T Mk 20 aircraft in Amendment 4.

The AD text itself contains no litigation history. The instrument lists amendment history and cross-references other ADs and technical notes but does not mention any court or tribunal proceedings, appeals, judicial challenges, or case law. The Background references other regulatory instruments and updates but does not include any reference to disputes or adjudicated decisions arising from this AD or its predecessors.

What is present in the AD

• Cross-references to other regulatory instruments (TNS documents and other ADs) and an explicit amendment chronology (Background) are recorded, but no adjudicative events are listed.

What is absent

• There is no information about legal challenges to the AD, no record of court or tribunal decisions testing the AD’s validity or enforcement, and no citation of cases or legal authority beyond administrative issuance. The AD does not provide a record of disputes about applicability, compliance, or exclusion based on the locally developed reinforcement kit.

Implication for researchers and practitioners

• Based solely on the text of this AD, there is no litigation history to report. A reader seeking to know whether this AD has been the subject of legal challenge will need to consult external legal or administrative records; the AD does not supply that information.

The AD contains a small number of detail points and cross-document dependencies that can cause misunderstandings if overlooked. These are set out expressly in the text.

1. Applicability hinges on both production origin and modification approval. The AD applies to "All English production (C1) all models and Portuguese production (T Mk 20) aircraft which have not been modified in accordance with a scheme approved by the authority (locally developed reinforcement kit)" (Applicability). Practitioners must check both the aircraft’s production origin/model and its modification status recorded against an "approved by the authority" scheme to determine whether the AD applies. Failure to check either element may lead to incorrect assumptions about applicability.

2. The inspection is specified "in accordance with" a named TNS. The Requirement directs inspection "in accordance with British Aerospace TNS CT(C1) No. 157, Issue 3, dated 28 May 1986." The AD does not reproduce the TNS content; operators must obtain and follow that TNS. The AD also instructs repetition "of paragraph 8 of the TNS",so paragraph numbering and content in TNS CT(C1) No. 157 and TNS CT(C1) No. 138 must be consulted directly to determine exact procedural steps and the content of paragraph 8.

3. Role Factor 4 shortens the interval. The Compliance provision reduces the repeat interval from six years to three years for aircraft "operated on a Role Factor of 4 (see TNS CT(C1) No. 138 Issue 5)." Thus, an operator’s operational use classification directly changes inspection frequency. Misclassification of Role Factor could inadvertently cause non‑compliance with the prescribed maximum intervals.

4. The exclusion requires authority-approved modification. The text excludes aircraft modified "in accordance with a scheme approved by the authority (locally developed reinforcement kit)." The AD does not specify how that approval is evidenced or recorded; operators must rely on their modification approval documentation and/or the authority’s records to establish exclusion status.

5. External documents mentioned but not included. The AD references TNS No. 138 Issue 5 and notes it is "the subject of UK CAA AD 2804 PRE 80 and CASA AD/DHC-1/12 Amendment 6." Practitioners must be aware that the Role Factor and other related definitions or procedures may be in those documents rather than in TNS No. 157 Issue 3. The AD does not reconcile potential differences; the operator must consult all referenced documents.

6. The AD does not set out enforcement measures or compliance evidence. The instrument mandates inspection but does not specify how compliance should be documented, nor does it state penalties for non-compliance within the printed text. That absence may lead to uncertainty about record-keeping and enforcement expectations unless clarified with the authority.

7. Effective date is shortly after signature. The AD is signed 16 June 2011 and "becomes effective on 22 June 2011." Operators with upcoming maintenance schedules around those dates must plan to ensure compliance from the effective date.

8. Narrow technical focus. The AD is limited to "radiographic inspection of the tailplane upper and lower spar flanges at the fuselage attachment brackets." Other structural areas or inspection methods are not addressed by this AD; operators should not infer broader obligations beyond the language used.

These points are direct consequences of the AD text and of its strict reliance on external technical notes and prior ADs. Missing or misread TNS clauses, Role Factor assignments, modification approval records, and failure to obtain the referenced TNS are practical sources of compliance risk indicated by the AD text.

Compliance under this AD is a procedural sequence driven by the text’s requirements and references. The AD provides the essential steps; operators and maintainers should follow them precisely and rely on the referenced TNS for technical detail.

Step 1 , Determine applicability

• Verify whether the aircraft is an English production C1 model or a Portuguese production T Mk 20. Confirm whether the aircraft "have been modified in accordance with a scheme approved by the authority (locally developed reinforcement kit)." If modified under an authority-approved scheme, the aircraft are excluded from the AD (Applicability).

Step 2 , Obtain the referenced documents

• Acquire British Aerospace TNS CT(C1) No. 157, Issue 3, dated 28 May 1986, because the AD requires inspection "in accordance with" that TNS (Requirement). Also obtain TNS CT(C1) No. 138 Issue 5, because the AD refers to the Role Factor definition and to paragraph 8 for repeat inspection intervals (Compliance; Background). The AD does not reproduce the TNS content; those documents provide the procedural and paragraph 8 detail.

Step 3 , Conduct the initial inspection

• For aircraft in scope, carry out the mandated "radiographic inspection of the tailplane upper and lower spar flanges at the fuselage attachment brackets" in accordance with the procedures and acceptance criteria in TNS CT(C1) No. 157 Issue 3 (Requirement; Background). Ensure the radiographic technique, view requirements and interpretation criteria are consistent with the TNS.

Step 4 , Record date of compliance and schedule repeats

• From the date of compliance with the initial inspection, schedule repeat inspections of paragraph 8 of the TNS "at intervals not exceeding 6 years," unless the aircraft is operated on Role Factor 4 (Compliance). If Role Factor 4 applies, schedule repeats at intervals not exceeding 3 years. Record the date of each inspection to demonstrate compliance with the AD’s timing requirement.

Step 5 , Determine Role Factor

• Consult TNS CT(C1) No. 138 Issue 5 to determine the appropriate Role Factor (the AD explicitly references that TNS for Role Factor guidance). If operational use places the aircraft on Role Factor 4, apply the shorter repeat interval.

Step 6 , Maintain modification and approval records

• If the aircraft has been modified with a locally developed reinforcement kit, ensure there is documentation of approval "by the authority" as stated in the AD. Maintain the approval documentation available to demonstrate that the aircraft is excluded from the AD where applicable (Applicability; Background).

Step 7 , Use competent personnel and equipment

• Since the inspection is radiographic, employ suitably qualified maintenance personnel or an approved maintenance organisation with the capability to perform radiographic inspection to the TNS standard. Ensure radiography equipment, exposure technique and interpretation are consistent with the TNS requirements.

Step 8 , Address findings in the TNS

• The AD requires inspection "in accordance with" the TNS. Any defect findings, thresholds for corrective action, or follow-up procedures should be handled as set out in TNS CT(C1) No. 157 Issue 3. The AD does not itself describe corrective actions; consult the TNS for required remediation steps if defects are discovered.

Step 9 , Monitor amendment and related ADs

• Note that the AD is Amendment 4 and references other ADs and TNS updates. Keep an eye on subsequent ADs or TNS revisions that may change procedures, intervals, or applicability. The AD records that previous amendments updated TNS references; further updates could alter compliance steps.

Step 10 , Coordinate with the authority where uncertain

• Where there is doubt about whether a locally developed reinforcement kit has been "approved by the authority," or where alternative inspection methods, intervals, or corrective actions are proposed, obtain written clarification or approval from the authority before departing from the AD’s requirements. The AD ties the exclusion specifically to "a scheme approved by the authority" (Applicability).

These steps reflect the specific obligations and cross-document dependencies listed in AD/DHC-1/22 Amendment 4. The AD provides the mandatory instruction and the referenced TNS contains the technical detail; compliance requires following both the AD text and the referenced TNS material, recording inspection dates, and maintaining documentation of modification approvals if used to claim exclusion.