{"id":"F2006B02536","name":"AD/AT 600/2 Amdt 1 - Aft Fuselage Structure Upper Longeron","slug":"ad-at-600-2-amdt-1-aft-fuselage-structure-upper-longeron","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41792,"registerId":"commonwealth-F2006B02536-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AT 600/2 Amdt 1 - Aft Fuselage Structure Upper Longeron","content":"![](image.001.png)\n\n![](image.001.png)  \nAIRWORTHINESS DIRECTIVE\n\nFor the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CASR 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\n![](image.001.png)  \n\nAirtractor 600 Series Aeroplanes\n\nAD/AT 600/2\n\nAmdt 1\n\n  \nAft Fuselage Structure Upper Longeron 10/2004\n\nApplicability: Model AT-602 aircraft, serial numbers 0337 through 0664. Requirement: For Model AT-602 aircraft, serial numbers 0337 through 0661:\n\n    Inspect the upper longeron on the left hand side of the fuselage frame, just forward of the vertical fin front spar attachment, for cracks in accordance with Snow Engineering Co. Service Letter (SL) No. 213A, dated 10 November 2003, as specified in SL No. 195, re-issued 10 November 2003.\n\n    2. For Model AT-602 aircraft, serial numbers 0662 through 0664:\n\nInspect the upper longeron on the left hand side of the fuselage frame, just forward of the vertical fin front spar attachment, for cracks in accordance with SL No. 213A, dated 10 November 2003, as specified in SL No. 195, re-issued 10 November 2003.\n\nNote: FAA AD 2004-15-15 Amdt 39-13749 refers.\n\nCompliance: 1. Initially inspect upon the accumulation of 700 total hours time in service or within the next 100 hours time in service after the last inspection required by the original issue of this Directive, whichever occurs later. Inspect thereafter at intervals not to exceed 100 hours time in service, until the upper longeron is replaced and modified in accordance with SL No. 213B, revised 10 November 2003.\n\n2. Initially inspect upon the accumulation of 1,750 total hours time in service or within the next 100 hours time in service after the last inspection required by the original issue of this Directive, whichever occurs later. Inspect thereafter at intervals not to exceed 100 hours time in service, until the upper longeron is replaced and modified in accordance with SL No. 213B, revised 10 November 2003.\n\nThis Airworthiness Directive becomes effective on 30 September 2004.\n\nAirtractor 600 Series Aeroplanes\n\nAD/AT 600/2 Amdt 1 (continued)\n\nBackground: The FAA received reports of three occurrences of cracks found on the left hand upper longeron and upper diagonal support tubes where they intersect on the left side of the fuselage frame just forward of the vertical fin front spar attachment point, on Model AT-602 aircraft. The cracks were found by the pilot and/or ground crew when they noticed excessive movement of the empennage due to the loss of torsional rigidity.\n\nAmendment 1 is issued in response to a new FAA AD, which changes the compliance times, and incorporates new and revised manufacturer service information that contains a terminating action for the repetitive inspection requirement.\n\n![](image.002.png)  \n\nDavid Villiers\n\nDelegate of the Civil Aviation Safety Authority 20 August 2004\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 8 September 2004.","sortOrder":0}],"analysis":{"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This amendment remains tightly focused on the original safety issue (cracked upper longerons on AT-602 aircraft). It does not expand to other aircraft models, other structural components, or unrelated safety concerns. The amendment merely refines compliance times and adds a terminating action for the existing inspection requirement — standard maintenance of an AD rather than scope creep."},"complexity_factors":["Short, single-purpose document focused on one specific structural defect","Only 2 distinct compliance pathways based on aircraft serial number ranges","References external technical documents (Snow Engineering Service Letters 213A, 213B, and 195) without reproducing their content","Simple conditional logic: 'whichever occurs later' comparisons for timing","No defined terms section — relies on standard aviation terminology","Minimal cross-referencing (only mentions FAA AD 2004-15-15 and CASR 1998 subregulation 39.1(1) in preamble)"],"plain_english_summary":"Owners/operators of Air Tractor AT-602 aircraft (S/N 0337–0664) must inspect the left upper longeron for cracks after specified flight hours and then every 100 hours until repaired. The FAA issued this AD after cracks were found that reduced fuselage stiffness and caused empennage wobble, risking loss of control. The amendment adds firm compliance times and allows a terminating action: replace and modify the longeron per the manufacturer’s Service Letter to end repetitive inspections."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":true,"description":"Amendment 1 altered the AD's compliance regime compared with the original issue by changing the compliance times (different initial inspection thresholds) and by incorporating revised manufacturer service information that provides a clear terminating action (replacement/modification per SL No. 213B). Mechanically, this shifts some long‑term burden from indefinite repetitive inspections to a one‑time modification option, and it updates the inspection schedule for later serial numbers (0662–0664) to a longer initial threshold."},"complexity_factors":["Short, single‑issue AD focused on one structural location (upper longeron)","Two serial‑number groups with different initial compliance thresholds (0337–0661 at 700 hrs; 0662–0664 at 1,750 hrs)","Single repeating inspection interval (every 100 hours) until terminating action","Terminology and compliance depend on external documents (SL No. 213A/213B and SL No. 195, and FAA AD reference)","No multi‑layered exceptions or multiple alternatives—simple stop condition (replace/modify per SL 213B terminates inspections)"],"plain_english_summary":"**What this instrument does (mechanically):**\n\n- This is an Airworthiness Directive (AD) that requires inspections and, ultimately, a modification/replacement of a structural member (the left‑hand upper longeron) on certain Airtractor AT‑602 aeroplanes.\n\n- **Which aircraft are affected (Applicability):** Model AT‑602 with serial numbers 0337 through 0664. The AD treats serial numbers 0337–0661 and 0662–0664 slightly differently for initial compliance timing (see Compliance below). (See \"Applicability\" and \"Requirement\".)\n\n- **What must be done now (Requirement):** Inspect the left side upper longeron at the fuselage frame location just forward of the vertical fin front spar attachment for cracks, following Snow Engineering Co. Service Letter (SL) No. 213A (as specified in SL No. 195 re‑issued 10 November 2003).\n\n- **When inspections must be done (Compliance):**\n  - For serials 0337–0661: first inspection at 700 total flight hours or within 100 hours after the last inspection required by the original AD (whichever is later). Then repeat inspections every 100 hours time‑in‑service until the longeron is replaced/modified per SL No. 213B (revised 10 November 2003).\n  - For serials 0662–0664: first inspection at 1,750 total flight hours or within 100 hours after the last inspection required by the original AD (whichever is later). Then repeat every 100 hours until the terminating modification in SL No. 213B is done.\n  - The SL No. 213B modification/replacement is the terminating action that ends the repetitive inspection requirement.\n\n- **Why the AD was issued (Background / stated reason):** The FAA reported three occurrences of cracks at the same longeron intersection on AT‑602s; those cracks reduced torsional rigidity and were noticed as excessive empennage movement. Amendment 1 updates compliance times and incorporates a terminating modification. (See \"Background\".)\n\n**Who pays and who decides:**\n\n- Aircraft operators (owners/maintenance organisations) pay for the inspections, any nondestructive testing, labour, downtime and for any replacement/modification parts and installation. The Civil Aviation Safety Authority delegate issued the AD and prescribes the inspection and terminating action instructions.\n\n**How behaviour changes and what choices operators have:**\n\n- Operators must add a recurring 100‑hour inspection task for the specified fuselage location until they perform the replacement/modification in SL No. 213B. They can either continue with recurring inspections (with associated cost and operational downtime) or perform the terminating modification to remove the inspection obligation.\n\n**Costs, incentives and trade‑offs (practical test of the stated purpose):**\n\n- The stated purpose is to detect and prevent structural cracking that reduces torsional rigidity. The direct costs are inspection labour and potential repair or replacement; recurring inspections create ongoing operating costs and aircraft downtime (opportunity cost). The terminating modification concentrates costs into a one‑off repair/modification but removes the recurring inspection burden.\n\n- Incentives created: operators with high utilisation will incur frequent inspection costs and therefore have a stronger incentive to carry out the terminating modification sooner than low‑utilisation operators. Operators facing tight maintenance budgets may defer modification and instead accept the recurring inspection cost until modification is affordable or until cracking is detected.\n\n**Implementation and compliance risks:**\n\n- Reliability of detection depends on inspection quality and adherence to the referenced Service Letters; poor inspections could leave cracks undetected. Parts availability, engineering hours and scheduling constraints are practical risks to carrying out the terminating action.\n\n**Cross‑references and terminating action:**\n\n- The AD depends on manufacturer service letters (SL No. 213A and 213B, and SL No. 195) for inspection and modification details, and it cites FAA AD 2004‑15‑15. The Service Letter 213B (revised 10 November 2003) is identified as the terminating action for the repeated inspections.\n\n(Sections referenced: Applicability; Requirement; Compliance; Background.)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-at-600-2-amdt-1-aft-fuselage-structure-upper-longeron","history":"/api/acts/ad-at-600-2-amdt-1-aft-fuselage-structure-upper-longeron/history","analysis":"/api/acts/ad-at-600-2-amdt-1-aft-fuselage-structure-upper-longeron/analysis","conflicts":"/api/acts/ad-at-600-2-amdt-1-aft-fuselage-structure-upper-longeron/conflicts","importantCases":"/api/acts/ad-at-600-2-amdt-1-aft-fuselage-structure-upper-longeron/important-cases","documents":"/api/acts/ad-at-600-2-amdt-1-aft-fuselage-structure-upper-longeron/documents"}}