{"id":"F2009L03644","name":"AD/AT 600/4 Amdt 4 - Engine Mount","slug":"ad-at-600-4-amdt-4-engine-mount","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":141477,"registerId":"commonwealth-F2009L03644-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Airtractor 600 Series Aeroplanes","sectionType":"division","heading":"Airtractor 600 Series Aeroplanes","content":"### Airtractor 600 Series Aeroplanes\n\n| AD/AT 600/4 Amdt 4 | Engine Mount | 11/2009 |\n| ------------------ | ------------ | ------- |\n\n| Applicability: | Model AT-602 aircraft, serial numbers 0001 through 1141.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |\n| Requirement:   | 1. For engine mounts without gussets installed, inspect the engine mount in accordance with Snow Engineering Co. SL No. 253 Revision C, dated17 April 2008:a. For aircraft with less than 5,000 hours time in service; at the initial and repetitive times specified in the Compliance section.b. For aircraft with 5,000 hours time in service or more; at the initial and repetitive times specified in the Compliance section.2. For engine mounts with gussets installed, inspect the engine mount in accordance with Snow Engineering Co. SL No. 253 Revision C, dated17 April 2008:a. For aircraft with less than 5,000 hours time in service; at the initial and repetitive times specified in the Compliance section.b. For aircraft with 5,000 hours time in service or more; at the initial and repetitive times specified in the Compliance section.Note: FAA AD 2009-11-05 Amdt 39-15915 refers. |\n| Compliance:    | 1. a. Initially, upon accumulating 1,300 hours time in service or within the next 100 hours time in service after 30 August 2007, whichever occurs later. Repetitively thereafter at intervals not to exceed 300 hours time in service.1. b. Initially, upon accumulating 5,000 hours time in service or within the next10 hours time in service after 30 July 2009, or within the next 100 hours time in service from the last inspection performed, whichever occurs later. Repetitively thereafter at intervals not to exceed 100 hours time in service.2. a. Initially, upon accumulating 1,300 hours time in service or within the next 100 hours time in service after 30 July 2009, whichever occurs later. Repetitively thereafter at intervals not to exceed 300 hours time in service.                                                                                                             |\n\n|             | 2. b. Initially, upon accumulating 5,000 hours time in service or within the next10 hours time in service after 30 July 2009, or within the next 100 hours time in service from the last inspection performed, whichever occurs later. Repetitively thereafter at intervals not to exceed 100 hours time in service.The compliance times remain unchanged by this issue of the Directive.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |\n| ----------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n|             | This Amendment becomes effective on 22 October 2009.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |\n| Background: | The FAA received reports of cracked engine mounts. Such cracking, unless detected and corrected, could result in failure of the engine mount and possible separation of the engine from the aircraft.Amendment 1 was prompted by reports received by the FAA of two Model AT-802A aircraft with cracked engine mounts below the initial compliance time. The FAA determined that the initial inspection is required when the aircraft reaches a total of 1,300 hours time in service.Amendment 2 retained the inspection actions of FAA AD 2007-13-17 and required incorporation of engine mount gussets as a mandatory terminating action for the repetitive inspection requirement.Amendment 3 was prompted by a report of a Model AT-602 aircraft with a crack completely through the gusset that was installed as required in FAA AD 2008-10-12. Consequently, this Directive requires repetitive inspections of engine mounts of all previously affected aircraft with or without gussets installed.Amendment 4 is issued to correct minor typographical errors in Compliance section paragraphs 1.b. and 2.b. There is no change to the technical requirements. |\n\n![](image.001.png)  \nDavid Villiers  \nDelegate of the Civil Aviation Safety Authority\n\n4 September 2009","sortOrder":0},{"sectionNumber":"AD/AT 600/4 Amdt 4","sectionType":"part","heading":"AD/AT 600/4 Amdt 4","content":"## AD/AT 600/4 Amdt 4","sortOrder":1},{"sectionNumber":"Engine Mount","sectionType":"part","heading":"Engine Mount","content":"## Engine Mount","sortOrder":2},{"sectionNumber":"11/2009","sectionType":"part","heading":"11/2009","content":"## 11/2009","sortOrder":3}],"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":4,"scope_assessment":{"changed":false,"description":"This is Amendment 4 of an existing Airworthiness Directive. The original AD addressed cracked engine mounts in Air Tractor aircraft. Amendment 4 explicitly states it only corrects 'minor typographical errors' in two paragraphs of the Compliance section and makes 'no change to the technical requirements.' The scope remains identical to Amendment 3 — repetitive inspections of engine mounts with or without gussets installed. The regulatory intent (preventing engine mount failure) has not expanded or shifted."},"complexity_factors":["Four distinct compliance pathways requiring cross-referencing between 'Requirement' and 'Compliance' sections","Multiple date thresholds (30 August 2007, 30 July 2009, 22 October 2009) and flight hour triggers (1,300 hours, 5,000 hours, 100 hours, 10 hours, 300 hours)","External technical reference required (Snow Engineering Co. SL No. 253 Revision C) — operators must obtain this document to perform the inspection","Nested conditional logic: 'whichever occurs later' clauses creating three-way comparisons for initial compliance dates","Amendment history references (Amendments 1-3) needed to understand full context, though not required for compliance","Cross-reference to FAA AD 2009-11-05 for additional context"],"plain_english_summary":"This AD mandates repetitive inspections of engine mounts on Air Tractor AT-602 aircraft (S/N 0001–1141), targeting agricultural and firefighting operators, to detect cracks that could lead to in‑flight engine separation. Inspection intervals depend on presence of reinforcement gussets and total flight hours. Amendment 4 only corrects typos in the Compliance text and does not alter any inspection requirements."},"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":false,"description":"Amendment 4 corrects minor typographical errors in Compliance paragraphs 1.b and 2.b but makes no change to technical requirements or inspection scope. The directive's applicability, inspection procedures (Snow Engineering SL No. 253 Rev C) and timing requirements remain as previously issued; compliance times are unchanged."},"complexity_factors":["Applicability limited to a specific model and serial-number range (AT-602, serials 0001–1141) which requires operators to verify scope precisely.","Different inspection regimes depending on presence or absence of gussets, and on total hours-in-service (<5,000 vs ≥5,000), increasing scheduling complexity.","Multiple conditional timing clauses with tight windows (initial at 1,300 or 5,000 hours, or within the next X hours after specific dates, and repetitive intervals of 300 or 100 hours) (see Compliance paragraphs 1.a/1.b/2.a/2.b).","Mandates compliance with an external document (Snow Engineering SL No. 253 Revision C) — operators must obtain and follow that specific service letter.","Reference to FAA ADs and previous amendments (background) creates a layered amendment history that can cause interpretive uncertainty for older inspections and terminating actions.","Amendment 4 purports only to fix typographical errors, but the presence of corrections in compliance timing increases the need for careful reading to avoid missed inspections.","Operational burden falls on owners/operators to schedule, fund and carry out inspections and any remedial work; CASA enforces compliance (effective date stated)."],"plain_english_summary":"Mandates recurring inspections of engine mounts on Airtractor AT‑602 aircraft (serial numbers 0001–1141), performed per Snow Engineering SL No. 253 Revision C. Inspection intervals differ by whether gussets are installed and by total hours‑in‑service, with initial checks at 1,300 or 5,000 hours and repetitive intervals of 300 or 100 hours.\n\nOwners/operators must schedule and pay for inspections and any repairs; CASA issued the directive to detect cracks that could cause engine‑mount failure. Amendment 4 corrects typographical errors only; technical requirements are unchanged."}},"importantCases":[],"_links":{"self":"/api/acts/ad-at-600-4-amdt-4-engine-mount","history":"/api/acts/ad-at-600-4-amdt-4-engine-mount/history","analysis":"/api/acts/ad-at-600-4-amdt-4-engine-mount/analysis","conflicts":"/api/acts/ad-at-600-4-amdt-4-engine-mount/conflicts","importantCases":"/api/acts/ad-at-600-4-amdt-4-engine-mount/important-cases","documents":"/api/acts/ad-at-600-4-amdt-4-engine-mount/documents"}}