{"id":"F2009L02830","name":"AD/AT/29 Amdt 1 - Engine Mount","slug":"ad-at-29-amdt-1-engine-mount","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":80106,"registerId":"commonwealth-F2009L02830-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Airtractor AT-300, 400 and 500 Series Ae","sectionType":"division","heading":"Airtractor AT-300, 400 and 500 Series Aeroplanes","content":"### Airtractor AT-300, 400 and 500 Series Aeroplanes\n\n| AD/AT/29 Amdt 1 | Engine Mount | 8/2009 |\n| --------------- | ------------ | ------ |\n\n| Applicability: | Model AT-400, AT-400A, AT-402, AT402A, and AT-402B aircraft, serial numbers 0001 through 1175.Model AT-502, AT-502A, AT-502B, and AT-503A aircraft, serial numbers 0001 through 2597.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement:   | A. Model AT-400, AT-400A, AT-402, AT-402A, AT-402B, AT-502, AT-502B, and AT-503A aircraft.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.B. Model 502A aircraft.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. |\n\n|             | 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.If crack damage is detected during any inspection, replace with a new engine mount or repair the engine mount. If choosing repair, contact Air Tractor, Inc. for repair instructions.Note: FAA AD 2009-11-05 Amdt 39-15915.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |\n| ----------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Compliance: | A. Model AT-400, AT-400A, AT-402, AT-402A, AT-402B, AT-502, AT-502B, and AT-503A aircraft.1.a. Initially, within the next 12 months after 3 July 2008. Repetitively thereafter at intervals not to exceed 12 months, until accumulating 5,000 hours time in service.1.b. Initially, upon accumulating 5,000 hours time in service or within the next 10 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 no to exceed 100 hours time in service.2.a. Initially, within the next 12 months after 30 July 2009. Repetitively thereafter at intervals not to exceed 12 months, until accumulating 5,000 hours time in service.2.b. Initially, upon accumulating 5,000 hours time in service or within the next 10 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 no to exceed 100 hours time in service.B. Model 502A aircraft.1.a. Initially, upon accumulating 1,300 hours time in service or within the next 100 hours time in service after 3 July 2008, whichever occurs later. Repetitively thereafter at intervals not to exceed 300 hours time in service. |\n\n|             | 1.b. Initially, upon accumulating 5,000 hours time in service or within the next 10 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 no 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.2.b. Initially, upon accumulating 5,000 hours time in service or within the next 10 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 no to exceed 100 hours time in service.                                                                                                                                                                                                                                                                                                                              |\n| ----------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n|             | This Amendment becomes effective on 30 July 2009.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |\n| Background: | Since the issue of FAA AD 2007-13-17, which affected Models AT-602, AT-802, and AT-802A aircraft, Air Tractor received a report of a Model AT-502B aircraft with a crack located where the lower engine mount tube is welded to the engine mount ring. In addition, Air Tractor developed gussets that, when installed in accordance with certain service letters, terminates the repetitive inspection requirement. Consequently, new FAA AD 2008-10-12 establishes new inspection actions for the AT-400 and AT-500 series aircraft and incorporates a mandatory terminating action for the repetitive inspections. The actions required by this Directive are intended to detect and correct cracks in the engine mount, which could result in failure of the engine mount and possible separation of the engine from the aircraft.Amendment 1 is issued in response to a new FAA AD, which 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. |\n\n![](image.001.png)  \nDavid Villiers  \nDelegate of the Civil Aviation Safety Authority\n\n18 June 2009","sortOrder":0},{"sectionNumber":"AD/AT/29 Amdt 1","sectionType":"part","heading":"AD/AT/29 Amdt 1","content":"## AD/AT/29 Amdt 1","sortOrder":1},{"sectionNumber":"Engine Mount","sectionType":"part","heading":"Engine Mount","content":"## Engine Mount","sortOrder":2},{"sectionNumber":"8/2009","sectionType":"part","heading":"8/2009","content":"## 8/2009","sortOrder":3}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":6,"scope_assessment":{"changed":true,"description":"The original AD (2008) established inspections with gusset installation as a 'terminating action' — meaning once gussets were installed, repetitive inspections could stop. Amendment 1 significantly expanded scope after new cracks were found in gusseted aircraft. The amendment now requires repetitive inspections for ALL aircraft regardless of gusset status, effectively nullifying the previous 'terminating action' concept and imposing permanent ongoing inspection obligations."},"complexity_factors":["Multiple overlapping compliance schedules based on four variables: aircraft model, presence/absence of gussets, flight hours threshold (1,300 vs 5,000 hours), and effective dates (3 July 2008 vs 30 July 2009)","Nested conditional logic: 8 distinct inspection pathways (2 gusset states × 2 hour thresholds × 2 model groups, with Model 502A having unique 1,300-hour triggers)","Complex temporal triggers using 'whichever occurs later' formulations across multiple reference dates","Cross-reference to external technical document (Snow Engineering Co. SL No. 253 Revision C) without reproducing its contents","Amendment structure that modifies previous AD requirements while maintaining some original compliance dates, creating layered effective dates","Termination actions that were themselves found insufficient, requiring the amendment"],"plain_english_summary":"This AD mandates repeated inspections of engine mounts on specified Air Tractor AT-300/400/500-series crop-dusters (affected serials/models) and requires repair or replacement if cracks are found. Inspection intervals vary by model, flight hours and whether reinforcement gussets are fitted. It affects owners/operators of these agricultural/firefighting aircraft and matters because cracked mounts can allow in‑flight engine separation — a catastrophic safety risk discovered in service, including after prior reinforcement."},"flash_summary":{"complexity_score":6,"scope_assessment":{"changed":true,"description":"This amendment expanded the practical scope of inspection obligations compared with the earlier approach. Earlier FAA action permitted gusset installation to serve as a terminating action for repetitive inspections; Amendment 1 requires repetitive inspections for engine mounts both with and without gussets because of a reported crack through an installed gusset (Background). Concretely, the amendment re-introduces recurring inspection obligations for aircraft and engine mounts that had previously been able to rely on gusset installation to stop repetitive inspections, increasing the number of aircraft/operators subject to ongoing inspection intervals and associated costs (Requirement; Compliance; Background)."},"complexity_factors":["Multiple affected models and explicit serial-number ranges (AT-400 family and AT-500 family; serial numbers specified)","Differentiated inspection rules for mounts with and without gussets (Requirement A and B)","Separate schedule for AT-502A with its own thresholds (Requirement B)","Multiple time/usage thresholds (less than 5,000 hours vs 5,000 hours or more; also a 1,300 hours threshold for AT-502A)","Mixed interval metrics: calendar-based (12 months) and flight-time-based (100 hours, 300 hours)","Staged initial-time conditions tied to dates and prior inspections (e.g. within next 12 months after 3 July 2008; within 10 hours after 30 July 2009; or within 100 hours from last inspection, whichever is later)","Reference to an external inspection standard (Snow Engineering Co. SL No. 253 Rev C) and to FAA ADs, creating cross-jurisdictional and document dependencies","Conditional terminating action history (previously-fitting gussets was treated as terminating in an earlier AD, but this amendment reintroduces inspections even for gusseted mounts)"],"plain_english_summary":"**What this directive does (mechanics)**\n\n- This airworthiness directive (AD) requires specific inspections of the engine mount on a set of Air Tractor aircraft models (AT-400 series and AT-500 series, with limited serial-number ranges as listed). The inspections must follow the procedures in Snow Engineering Co. Service Letter No. 253, Revision C (dated 17 April 2008).\n\n- Inspections are required both for engine mounts that have *no gusset* fitted and for mounts that *do have a gusset*. The inspections are periodic and the timing depends on the aircraft model and the hours the aircraft has accumulated (see “timing” below).\n\n- If an inspection finds a crack in the engine mount, the owner/operator must either replace the engine mount with a new one or repair it. If choosing repair, the AD requires contacting Air Tractor, Inc. for repair instructions (Requirement, last paragraph).\n\n- The AD sets different initial and repetitive inspection schedules depending on:\n  - whether the mount has gussets or not (Requirement A and B);\n  - the model variant (AT-400 family, AT-500 family, or AT-502A has separate timings);\n  - whether the aircraft has accumulated less than 5,000 hours time-in-service (TIS) or 5,000 hours or more; and\n  - in one case (AT-502A) an earlier 1,300-hour threshold applies for starting periodic (less frequent) inspections.\n\n- Typical inspection intervals used in the directive are:\n  - Annual (every 12 months) inspections for mounts on aircraft under certain hours thresholds; or\n  - Frequent inspections every 100 hours TIS after 5,000 TIS (or soon after specified dates); or\n  - For some AT-502A schedules a 300-hour repetitive interval applies for mid-life inspections (Compliance section).\n\n- The AD became effective on 30 July 2009 and references FAA AD 2009-11-05 and earlier FAA ADs that prompted these requirements (Background).\n\n**Who this affects**\n\n- Aircraft owners, operators, and maintenance providers for the listed Air Tractor models and serial numbers. The directive is prescriptive — it creates a mandatory inspection and repair obligation tied to specific aircraft by model and serial number (Applicability table; Requirement and Compliance sections).\n\n- Repair suppliers and Air Tractor, Inc., because the AD directs operators to contact Air Tractor for repair instructions when a repair is chosen (Requirement).\n\n- Regulators and approved maintenance organisations who must record compliance and ensure inspections meet the required Service Letter procedures.\n\n**Why it matters (official rationale and mechanical effect)**\n\n- The stated purpose is to detect and correct cracking in the engine mount tubes/ring weld area. Undetected cracks could lead to engine mount failure and possible separation of the engine from the aircraft (Background).\n\n- Mechanically, the AD enforces regular inspections at intervals tied to aircraft usage and age. It removes any previous assumption that installing gussets completely removes the need for future inspections — this amendment requires inspections even on mounts with gussets because of at least one reported failure where the gusset itself cracked (Background; Amendment 1 explanation).\n\n**Costs, incentives and trade-offs (practical effects)**\n\n- Who pays: aircraft owners/operators pay for the inspections, any subsequent repairs or replacements, and aircraft downtime while work is done (Requirement; Compliance).\n\n- Who decides: the regulator (via this AD) decides the inspection standard and timing; the owner/operator decides whether to replace or repair a cracked mount, but if repairing they must follow Air Tractor repair instructions (Requirement).\n\n- Behaviour changes required: schedule and do the mandated inspections at the specified intervals; if cracks are found, either replace the mount or obtain and follow repair instructions from the manufacturer; keep maintenance records showing compliance.\n\n- Direct financial costs: inspection labour and parts costs, potential need to source replacement engine mounts, and operational downtime. These costs are concentrated on the owners/operators of the affected aircraft (Applicability; Requirement).\n\n- Potential supply and implementation risks: if a large number of aircraft require replacement mounts or manufacturer-authorised repairs at once, there could be temporary supply constraints for parts or qualified repair instructions. The AD points operators to Air Tractor for repairs, which centralises the repair route (Requirement).\n\n- Compliance burden and frequency: complexity of compliance rises with the more frequent inspection intervals (every 100 hours TIS) after 5,000 hours in service for many models, and a separate 300-hour cycle for intermediate inspections on some models (Compliance A & B). This creates ongoing recurring operational costs rather than a one-off fix.\n\n- Effect on private choice and market outcomes: owners retain choice between replacing and repairing the mount, but the AD constrains repair options by requiring that repairs follow Air Tractor instructions (Requirement). That can concentrate demand for sanctioned repair procedures and possibly parts or authorised service providers.\n\n- Trade-offs and opportunity costs: the AD trades operator cost and downtime (inspections/repairs) for reduced risk of catastrophic engine-mount failure. The timing thresholds (e.g. annual vs 100-hour cycles) reflect a risk-management decision by the regulator.\n\n**Implementation risks and administrative discretion**\n\n- The AD specifies the inspection standard (Snow Engineering SL No. 253 Rev C) and thus limits discretion in how the inspection is done (Requirement). Discretion remains with the operator when choosing replace vs repair, but repairs must follow manufacturer guidance (Requirement).\n\n- The effectiveness of the safety outcome depends on timely inspections, accurate crack detection during inspections, availability of replacement mounts/approved repairs, and correct implementation of repair instructions.\n\n**Source claims vs mechanical facts**\n\n- The directive’s background states that it responds to reported cracks — including a crack through a previously fitted gusset — and that the amendment restores mandatory inspections even where gussets were fitted (Background). That is stated as the reason for the requirement; the AD implements inspections and repair-or-replace obligations accordingly (Requirement, Compliance)."},"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"}},"importantCases":[],"_links":{"self":"/api/acts/ad-at-29-amdt-1-engine-mount","history":"/api/acts/ad-at-29-amdt-1-engine-mount/history","analysis":"/api/acts/ad-at-29-amdt-1-engine-mount/analysis","conflicts":"/api/acts/ad-at-29-amdt-1-engine-mount/conflicts","importantCases":"/api/acts/ad-at-29-amdt-1-engine-mount/important-cases","documents":"/api/acts/ad-at-29-amdt-1-engine-mount/documents"}}