{"id":"F2006B08804","name":"AD/DC3/29 Amdt 4 - Lower Centre Section Skin and Structure","slug":"ad-dc3-29-amdt-4-lower-centre-section-skin-and-structure","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":52173,"registerId":"commonwealth-F2006B08804-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DC3/29 Amdt 4 - Lower Centre Section Skin and Structure","content":"![](image.001.png)  \n![](image.002.png)  \nDouglas DC3 Series Aeroplanes\n\nAIRWORTHINESS DIRECTIVE\n\n![](image.002.png)\n\n![](image.002.png)  \nFor the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/DC3/29 Amdt 3 and issues the following AD under subregulation 39.1 (1) of CAR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.\n\nAD/DC3/29\n\nAmdt 4\n\n  \nLower Centre Section Skin and Structure 7/2000\n\nApplicability: All models.\n\nRequirement: 1. Visually inspect those parts of the front face of the wing front spar, the lower spar cap and lower wing skin and doublers accessible from within the main landing gear bay and through the access holes in the landing gear drag strut tunnels between approximately Wing Station (WS) 90 and WS 130.\n\n    2. For aircraft which have not been modified with the repair or preventive doublers at both WS 94.25 and WS 127.75 in accordance with McDonnell Douglas (MD) Service Bulletin (SB) 229, any revision, or McDonnell Douglas Service Bulletin 263, any revision up to and including Revision 8, or McDonnell Douglas Service Rework Drawing (SRD) SR03578003:\n\nNote 1: Alternative designs of repair or preventive doublers are acceptable for the purposes of this AD only where they have been assessed and approved as at least equivalent to the above data, by the holder of an appropriate CAR 35 design authorisation.\n\n    Incorporate access holes in accordance with MD SRD03548001, Revision A;\n\nNote 2: Aircraft which have previously been modified to incorporate access holes, do not have to be re-modified provided that the necessary access and visibility can be obtained.\n\n    b. Inspect the wing using the visual and radiographic procedures specified in MD SRD SR03578001 or MD SRD SR03578002 Revision A, whichever is applicable; and\n\nNote 3: Radiographic Technique DCA NCI/R/8 is an acceptable alternative procedure provided that for exposures 4 and 5 additional film is placed on the lower wing skin to inspect the lower spar between the drag strut fairing and the centre line of the nacelle.\n\n    c. Modify the wing to incorporate wing skin doublers at both WS 94.25 and\n\n127.75 in accordance with MD SRD SR03578003.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n    3. For aircraft which have been modified to incorporate wing skin doublers in accordance with SB 229, SB 263 and/or SRD SR03578003, inspect the wing using the visual procedure specified by SRD03578001 or SRD SR03578002 Revision A, whichever is applicable.\n\nNote 4: Transport Canada AD CF-92-15 refers.\n\nCompliance: For Requirement Para 1: Inspect before exceeding 500 hours time in service since last inspected in accordance with the previous issue of this AD, and thereafter at intervals not exceeding 500 hours time in service. In addition, inspect before further flight following flight in severe turbulence or following a heavy landing.\n\nFor Requirement Para 2.a: Incorporate the access holes not later than the next inspection in accordance with Requirement Para 2.b.\n\nFor Requirement Para 2.b: Inspect before exceeding 900 hours time in service since last inspected in accordance with the previous issue of this AD, or within 100 hours time in service after (date of issue), whichever occurs later, and thereafter at intervals not exceeding 900 hours time in service.\n\nFor Requirement Para 2.c: Modify the wing before exceeding 900 hours time in service after 27 April 1995, or within 100 hours time in service after (date of issue), whichever occurs later.\n\nFor Requirement Para 3: Inspect before exceeding 2000 hours time in service after 1 September 1969, or before exceeding 2000 hours time in service since last inspected in accordance with the previous issue of this AD, whichever occurs later, and thereafter at intervals not exceeding 2000 hours time in service.\n\nThis Amendment becomes effective on 13 July 2000.\n\nBackground: Previous issues of this AD promulgated inspection and modification in accordance with early issues of the reference documents. Amendment 3 introduced an additional modification to improve access for inspection; revised the inspection procedures; and required mandatory incorporation of the preventive doublers at the critical wing stations. These changes were prompted by an in-flight wing separation in Canada, and were intended to bring the Australian AD into line with recommendations from McDonnell Douglas and the FAA. FAA AD 92-06-15 refers.\n\nSubsequently the Authority was made aware that the requirement of Amdt 3 was ambiguous and that it provided a loophole whereby aircraft modified in accordance with SB 229, were not required to comply with Paragraphs 2.a, b or c. However, SB 229 specifies modification at WS 127.75 only, but not WS 94.25. This is contrary to the intent of the AD, which was to install the reinforcing doublers at both locations. Airworthiness inspectors have reported a number of aircraft in service in Australia which do not have the WS 94.25 modification and which, by virtue of the AD wording, are not receiving the detailed visual and radiographic inspection at either location. It has also been reported that some aircraft have doublers installed which do not appear to conform to the SB or SRD specifications.\n\nThis issue makes it clear that both wing stations are critical and that modification and inspection at both locations is required, and that the modifications must accord with the specified data. Aircraft which are in full compliance with the intent of the previous issue as outlined above, including correct doubler installation and detailed visual and radiographic inspection at both locations WS 94.25 and WS 127.75, left and right sides, need no additional work as a result of this amendment. Ongoing inspection is of course still required.\n\nAmendment 3 of this directive became effective on 27 April 1995.\n\n![Signature of William Ronald Smith Delegate of the Civil Aviation Safety Authority](image.003.png)  \n\nWilliam Ronald Smith\n\nDelegate of the Civil Aviation Safety Authority 15 May 2000\n\n![](image.002.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 14 June 2000.","sortOrder":0}],"analysis":{"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"},"flash_summary":{"complexity_score":6,"scope_assessment":{"changed":false,"description":"Amendment 4 does not expand the original safety objective. It removes an ambiguity in Amendment 3 that had effectively narrowed enforcement (by allowing aircraft modified only at WS 127.75 to escape further inspection) and re‑establishes the original intent that both WS 94.25 and WS 127.75 must be modified and inspected in accordance with the specified MD SB/SRD (Background; Requirement Paras 2–3)."},"complexity_factors":["Multiple external technical references required (McDonnell Douglas SB 229, SB 263, SRD SR03578003, SRD03548001, SRD03578001/02) increasing compliance detail and record reliance (Requirement Paras 2–3; Notes).","Differing workflows depending on prior modifications: unmodified aircraft follow Para 2 steps; previously modified aircraft follow Para 3 (Requirement Paras 2–3).","Multiple and staggered compliance intervals and event‑triggers: inspections at 500h, 900h, and 2000h intervals and mandatory inspections after severe turbulence or heavy landing (Compliance).","Technical inspection methods include both visual and radiographic procedures, with an alternative radiographic technique permitted under specified conditions (Requirement Para 2.b; Note 3).","Alternative doubler designs allowed only if assessed by holder of CAR 35 design authorisation, creating an approval gate and discretionary certification burden (Note 1).","Retroactive interaction with prior AD wording and past modifications: this amendment resolves an ambiguity in Amdt 3 that had allowed incomplete compliance (Background).","Operational access requirements (incorporation of access holes per SRD) and the need to inspect left and right sides add practical maintenance complexity (Requirement Para 2.a; Note 2)."],"plain_english_summary":"This Airworthiness Directive requires operators of Douglas DC‑3 series aeroplanes to inspect the lower centre wing (roughly WS 90–130) and, unless already properly modified, to install access holes, perform visual and radiographic inspections, and fit wing skin doublers at both WS 94.25 and WS 127.75 in accordance with specified McDonnell Douglas service data. It clarifies a prior ambiguity after an in‑flight wing separation by making inspections and doublers mandatory at both stations and by tying alternative designs to authorised approval."},"kimi_summary":{"content_quality":"ok","complexity_score":6,"scope_assessment":{"changed":true,"description":"This amendment (Amdt 4) explicitly addresses scope creep from the previous version. The original Amdt 3 intended to mandate reinforcements at TWO wing stations (WS 94.25 and WS 127.75), but ambiguous drafting created a loophole where aircraft modified under Service Bulletin 229 (which only covers WS 127.75) escaped inspection requirements entirely. Amdt 4 narrows the scope back to the original safety intent by clarifying that BOTH locations require modification and inspection regardless of partial compliance history. The scope has effectively been tightened to prevent the safety regime from being undermined by partial modifications."},"complexity_factors":["Multiple conditional requirement pathways based on aircraft modification history (Requirements 1, 2, and 3 apply to different aircraft configurations)","Nested sub-requirements (2.a, 2.b, 2.c) with interdependent compliance deadlines","Cross-references to external technical documents: 4 McDonnell Douglas Service Bulletins/Drawings (SB 229, SB 263, SRD SR03578001, SRD SR03578002, SRD SR03578003) plus Transport Canada AD CF-92-15 and FAA AD 92-06-15","Technical aviation terminology requiring specialized knowledge (Wing Station references, doubler specifications, radiographic procedures)","Multiple compliance time calculations based on different baselines (hours since last inspection, hours since specific dates, hours after issue date, calendar date of 27 April 1995)","Four detailed notes qualifying main requirements with alternative compliance methods and exceptions","Amendment structure requiring understanding of previous versions (Amdt 3) and their loopholes to comprehend current intent"],"plain_english_summary":"The CASA Airworthiness Directive mandates tighter inspections and structural reinforcements for all Douglas DC‑3s in Australia after an in‑flight wing separation overseas. It requires recurring visual, detailed and radiographic inspections and installation of reinforcing plates where missing, affecting owners, operators and maintenance engineers. The rule closes a loophole that let some partially reinforced planes avoid checks, addressing metal fatigue risk in these aging, operational vintage aircraft."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dc3-29-amdt-4-lower-centre-section-skin-and-structure","history":"/api/acts/ad-dc3-29-amdt-4-lower-centre-section-skin-and-structure/history","analysis":"/api/acts/ad-dc3-29-amdt-4-lower-centre-section-skin-and-structure/analysis","conflicts":"/api/acts/ad-dc3-29-amdt-4-lower-centre-section-skin-and-structure/conflicts","importantCases":"/api/acts/ad-dc3-29-amdt-4-lower-centre-section-skin-and-structure/important-cases","documents":"/api/acts/ad-dc3-29-amdt-4-lower-centre-section-skin-and-structure/documents"}}