{"id":"F2006L03876","name":"AD/AT 600/6 - Upper Rudder Hinge","slug":"ad-at-600-6-upper-rudder-hinge","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":60805,"registerId":"commonwealth-F2006L03876-current","compilationNumber":null,"startDate":"2026-04-02","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 600/6 | Upper Rudder Hinge | 1/2007 |\n| ----------- | ------------------ | ------ |\n\n| Applicability: | Model AT-602 aircraft, serial numbers 602-0337 through 602-1138.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |\n| -------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement:   | 1. Visually inspect the rudder and vertical hinge attachment for loose fasteners; and inspect the rudder and vertical fin skins, spars, hinges, and brackets for cracks and/or corrosion, in accordance with Snow Engineering Co. Service Letter (SL) No. 247 dated 14 August 2005, revised 17 May 2006.2. If damage is detected during any inspection, replace any damaged parts with new parts, and install the external doubler at the upper rudder hinge, in accordance with SL No. 247 and Snow Engineering Co. Process Specification No. 145 dated 6 December 1991.3. Install the external doubler at the upper rudder hinge in accordance with SL No. 247 and Snow Engineering Co. Process Specification No. 145.As of the effective date of this Directive, no rudder is to be installed unless the external doubler at the upper rudder hinge is incorporated.Note 1: Installation of the external doubler at the upper rudder hinge is terminating action for the Requirement 1 inspection requirements.Note 2: FAA AD 2006-23-14 Amdt 39-14826 refers. |\n| Compliance:    | 1. Unless the initial inspection is already accomplished, upon the accumulation of 3,500 hours time in service or within 100 hours time in service after 18 January 2007, whichever occurs later. Thereafter, inspect at intervals not to exceed 100 hours time in service.2. Before further flight.3. Upon the accumulation of 5,000 hours time in service or within 100 hours time in service after 18 January 2007, whichever occurs later; unless already accomplished.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |\n|                | This Airworthiness Directive becomes effective on 18 January 2007.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |\n\n| Background: | The FAA received two reports of in-flight rudder separation from the vertical fin at the upper attach hinge area, and other reports of aircraft with loose hinges, skin cracks, or signs of repairs to the affected area. Hinge failure adversely affects ability to control yaw and has led to the rudder folding over in flight. This condition could allow the rudder to contact the elevator and affect ability to control pitch, with subsequent loss of control. |\n| ----------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n\n![](image.001.png)  \nDavid Villiers  \nDelegate of the Civil Aviation Safety Authority\n\n23 November 2006","sortOrder":0},{"sectionNumber":"AD/AT 600/6","sectionType":"part","heading":"AD/AT 600/6","content":"## AD/AT 600/6","sortOrder":1},{"sectionNumber":"Upper Rudder Hinge","sectionType":"part","heading":"Upper Rudder Hinge","content":"## Upper Rudder Hinge","sortOrder":2},{"sectionNumber":"1/2007","sectionType":"part","heading":"1/2007","content":"## 1/2007","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"This directive stays within the original safety objective: address upper rudder-hinge failures on a specific subset of AT-602 aircraft. It does not expand the affected fleet, add unrelated obligations, or extend regulatory reach beyond inspection, repair and installation of the external doubler. The measure replaces recurring inspection with a terminating modification but does not materially change the original purpose of remedying hinge separation and preventing loss of control."},"complexity_factors":["Single-model, limited serial-number applicability (narrow scope)","Three primary mandatory actions (inspect; replace and install doubler if damage; install doubler regardless)","Simple compliance timeline but with conditional phrasing (“whichever occurs later”)","Recurring inspection interval specified (every 100 hours) until terminating action","References to two external Snow Engineering documents (SL No.247 and Process Specification No.145) and an FAA AD (adds cross-reference complexity)","No extensive defined-terms section or nested exceptions"],"plain_english_summary":"**What this directive does (mechanical effect)**\n\n- Applies to Airtractor Model AT-602 aeroplanes, serial numbers 602-0337 through 602-1138.\n- Requires operators to visually inspect the rudder and the upper rudder hinge area (fasteners, skins, spars, hinges, brackets) following Snow Engineering Co. Service Letter No. 247 (14 Aug 2005, rev. 17 May 2006).\n- If any damage (including loose fasteners, cracks or corrosion) is found, damaged parts must be replaced with new parts and an external doubler must be installed at the upper rudder hinge in accordance with Snow Engineering Co. Process Specification No. 145 (6 Dec 1991) and SL No. 247.\n- Requires installation of the external doubler at the upper rudder hinge as a mandated modification; after the doubler is fitted, the recurring inspection requirement for the upper hinge is ended (i.e. installation is the terminating action).\n- Prohibits installing a rudder on an affected aeroplane unless the external doubler is incorporated.\n- Cross-references FAA Airworthiness Directive (AD 2006-23-14).\n\n**When inspections and actions must occur (compliance timing)**\n\n- Initial inspection: at 3,500 hours time-in-service, or within 100 hours time-in-service after 18 January 2007, whichever is later (unless already done).\n- Recurring inspections: every 100 hours time-in-service thereafter until the doubler is installed.\n- If damage is found during an inspection: replace damaged parts and install the doubler **before further flight**.\n- Mandatory installation of the external doubler: by 5,000 hours time-in-service, or within 100 hours time-in-service after 18 January 2007, whichever is later (unless already done).\n\n**Why the regulator issued this (stated rationale)**\n\n- The FAA reported cases of the rudder separating from the vertical fin at the upper attach hinge; other reports described loose hinges, skin cracks or repairs in that area. Hinge failure can reduce yaw control, can cause the rudder to fold over and strike the elevator, and may lead to loss of control. The directive aims to prevent these unsafe conditions by detecting damage early and by reinforcing the hinge with an external doubler.\n\n**Who is affected and who pays**\n\n- Affected parties: owners and operators of the specified AT-602 aircraft and the maintenance organisations who service them.\n- Direct costs: operators pay for inspections, any part replacements, labour for installing the external doubler, and aircraft downtime while work is done.\n- After a one-off modification (installation of the external doubler), the recurring inspection burden is removed for that area.\n\n**Implementation mechanics, incentives and operational trade-offs**\n\n- Inspection-and-repair path: operators can choose to continue periodic inspections (every 100 hours) until they complete the specified modification, or they can install the doubler earlier to stop the recurring inspections.\n- Trade-off: the doubler imposes an up-front cost and downtime but eliminates ongoing inspection costs and reduces the immediate risk of hinge failure. Operators decide based on their maintenance schedules, parts availability and cost of aircraft downtime.\n- Compliance depends on access to the Snow Engineering service documents and to the doubler parts and qualified maintenance personnel able to follow Process Specification No. 145.\n\n**Compliance burden and practical risks**\n\n- Administrative and operational burden is moderate: the directive references two external supplier documents (SL No. 247 and Process Specification No. 145) that must be followed exactly, which requires operators and maintainers to obtain and apply those documents.\n- Implementation risks include parts availability, scheduling of maintenance slots, and ensuring replacement parts conform to the specified process. If parts or approved repair capability are scarce, operators may face extended grounding or restricted operations.\n\n**Market effects and distribution of benefits/costs**\n\n- Concentrated benefits: improved safety for operators and their passengers for the affected serial-number range.\n- Concentrated costs: owners/operators of the specified aircraft bear direct costs (inspection, replacement, modification). Maintenance providers may see increased work (inspection and doubler installation revenue).\n- No direct change to aircraft ownership rules, contractual freedoms, or competition law. The directive prescribes technical work and timing; it does not create new taxes, subsidies, or licensing beyond existing maintenance requirements.\n\n**Source claims vs practical consequences**\n\n- The directive’s stated safety justification is supported by reported incidents of hinge separation and associated damage. The mechanical remedy (install external doubler) is presented as both corrective (repair damaged parts) and preventative (mandatory installation).\n- The practical consequence is a one-off mandated modification to reduce future inspection needs for that hinge area at the expense of immediate modification cost and potential downtime.\n\n(Referenced items: “Applicability”, “Requirement”, “Compliance”, and “Background” sections of the directive.)"},"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 is a standard airworthiness directive with a focused, narrow scope: addressing a specific mechanical failure mode in a specific aircraft model. The scope remains tightly constrained to the upper rudder hinge issue as originally identified."},"complexity_factors":["Multiple compliance deadlines with conditional triggers ('whichever occurs later')","Three distinct requirements with different timelines and conditions","Cross-references to external technical documents (Snow Engineering Service Letter 247 and Process Specification 145) that are not reproduced in the directive","Reference to US FAA AD 2006-23-14 for additional context","Nested conditions: Requirement 2 only applies 'if damage is detected', creating a conditional branch","Technical aviation terminology requiring specialist knowledge (time in service, external doubler, terminating action)"],"plain_english_summary":"This AD requires owners/operators of specified Air Tractor AT-602s (S/N 602‑0337–602‑1138) to inspect and repair the upper rudder hinge and nearby structure because hinge failures have led to in‑flight rudder separations and loss of control. Damaged parts must be replaced and an external reinforcing doubler installed; repetitive 100‑hour inspections continue until the doubler is fitted. The doubler must be installed by 5,000 flight hours (or within 100 hours after 18 Jan 2007), and rudders without doublers cannot be newly fitted."}},"importantCases":[],"_links":{"self":"/api/acts/ad-at-600-6-upper-rudder-hinge","history":"/api/acts/ad-at-600-6-upper-rudder-hinge/history","analysis":"/api/acts/ad-at-600-6-upper-rudder-hinge/analysis","conflicts":"/api/acts/ad-at-600-6-upper-rudder-hinge/conflicts","importantCases":"/api/acts/ad-at-600-6-upper-rudder-hinge/important-cases","documents":"/api/acts/ad-at-600-6-upper-rudder-hinge/documents"}}