{"id":"F2006B09909","name":"AD/F50/79 Amdt 4 - Control Surfaces Leading Edge Attachment","slug":"ad-f50-79-amdt-4-control-surfaces-leading-edge-attachment","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":55104,"registerId":"commonwealth-F2006B09909-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F50/79 Amdt 4 - Control Surfaces Leading Edge Attachment","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 revokes Airworthiness Directive (AD) AD/F50/79 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\n![](image.001.png)  \n\nFokker F50 (F27 Mk 050) Series Aeroplanes\n\nAD/F50/79\n\nAmdt 4\n\n  \nControl Surfaces Leading Edge Attachment 11/2002\n\nApplicability: Model F27 Mk 050, Mk 0502, and Mk 0604 aircraft, all serial numbers.\n\nRequirement: 1. Check the torque value of the elevator leading edge attachment screws and take corrective action, as necessary, in accordance with the Accomplishment Instructions of Fokker Service Bulletin (SB) F50-55-007 Revision 2, dated 17 June 2002.\n\n    2. Check the torque value of the rudder leading edge section attachment screws and take corrective action, as necessary, in accordance with the Accomplishment Instructions of Fokker SB F50-55-009 Revision 2, dated 17 June 2002.\n    3. Check the torque value of the aileron leading edge sections attachment screws and take corrective action, as necessary, in accordance with the Accomplishment Instructions of Fokker SB F50-57-020 Revision 2, dated 17 June 2002.\n    4. Modify the flight control surface leading edge section attachments by installing additional locking devices as follows:\n\n    for the rudder; in accordance with Fokker SB F50-55-010 Revision 2, dated 17 June 2002.\n\n    b. for the ailerons; in accordance with Fokker SB F50-57-021 Revision 2, dated 17 June 2002.\n\n    c. for the elevators; in accordance with Fokker SB F50-55-008 Revision 3, dated 17 June 2002.\n\nNote 1: Compliance with Requirement 4 constitutes terminating action for the actions required by Requirements 1, 2, and 3.\n\nNote 2: Netherlands CAA AD 2000-131/2 refers.\n\nCompliance: 1. Within the next 6 months after 31 October 2002 or at the expiry of the 12 calendar months interval as required by the previous issue of this Directive, whichever occurs first, and thereafter at intervals not to exceed 6 calendar months; until compliance with Requirement 4.\n\n    2. Within the next 12 months after 31 October 2002 or at the expiry of the 4,000 flight hours or 24 calendar months interval as required by the previous issue of this Directive, whichever occurs first, and thereafter at intervals not to exceed 12 calendar mont hs; until compliance with Requirement 4.\n\n    3. Within the next 6 months after 31 October 2002 or at the expiry of the 12 calendar months interval as required by the previous issue of this Directive, whichever occurs first, and thereafter at intervals not to exceed 6 calendar months; until compliance with Requirement 4.\n    4. Within the next 24 calendar months after 31 October 2002 or 15 years time- since-new of the aircraft, whichever occurs first.\n\nThis Amendment becomes effective on 31 October 2002.\n\nBackground: The RLD received an operator’s report of an incident where, after landing, the elevator control was found to be binding in the fully “up” position. Subsequent investigation revealed that an attachment screw had come loose, moving out of the elevator leading edge section against the horizontal stabiliser. This condition could lead to further incidents of elevator binding, possibly resulting in loss of control.\n\nAmendment 1 expanded the AD inspection to include attachment screws of the rudder and aileron leading edges.\n\nAmendment 2 expanded the compliance requirements for the rudder leading edge attachment screws; as a result of a recent evaluation which concluded that the rudder is of less airworthiness concern than originally envisaged, and the requirement for rudder removal to accomplish the task.\n\nAmendment 3 required modification action by installing additional locking devices; which terminates the on- going repetitive check requirements.\n\nAmendment 4 is issued in response to a new issue of the related CAA-NL AD which reduces the intervals for inspection and re-tightening of the flight control surfaces leading edge attachment screws, as well as introduce a new limit for compliance with the required modification. The AD was prompted by an operator report of in- flight vibration and subsequent finding of a loose elevator leading edge section that had been inspected 7 months previously.\n\nAmendment 3 of this Airworthiness Directive became effective on 22 March 2001.\n\nAmendment 2 of this Airworthiness Directive became effective on 30 December 1999.\n\nAmendment 1 of this Airworthiness Directive became effective on 12 August 1999.\n\nThe original issue of this Airworthiness Directive became effective on 10 September 1999.\n\n![](image.002.png)  \n\nDavid Charles Punshon\n\nDelegate of the Civil Aviation Safety Authority 19 September 2002\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 9 October 2002.","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":4,"scope_assessment":{"changed":true,"description":"The AD has expanded in scope since the original issue. The original directive addressed an elevator leading edge attachment issue; subsequent amendments (1–3) extended the inspection requirements to include rudder and aileron attachment screws and added a modification (additional locking devices) as a terminating action. Amendment 4 further tightened inspection intervals and imposed a firm limit (24 months after 31 Oct 2002 or 15 years time‑since‑new) by which the mandatory modification must be carried out. In short: from a single‑surface inspection the instrument evolved into a multi‑surface inspection regime plus a mandated modification with a defined compliance deadline, broadening both the technical scope and the operational burden on operators."},"complexity_factors":["Four distinct mandatory actions (Requirements 1–4) with different technical tasks (inspection/retorque vs modification).","Multiple referenced Fokker Service Bulletins with specific revision numbers and dates (6 SB references across Requirements 1–4).","Different compliance timing for each Requirement with conditional phrasing (first due dates defined relative to 31 Oct 2002 or previous inspection intervals, and recurring intervals until modification).","Terminating action (Requirement 4 / Note 1) that cancels repetitive requirements, creating procedural dependency.","Cross‑reference to Netherlands CAA AD and several earlier amendments (historical layering of requirements).","An upper time‑since‑new limit for mandatory modification (15 years) that interacts with calendar‑based deadlines.","Applicability limited to specific models and all serial numbers (narrow scope but requires fleet‑level tracking)."],"plain_english_summary":"**What this directive does (mechanically)**\n\n- Requires operators of Fokker F50 (F27 Mk 050, Mk 0502 and Mk 0604) aeroplanes to inspect and, where necessary, correct the torque of the attachment screws that secure the leading edge sections of the elevator, rudder and ailerons (Requirements 1–3).  \n- Requires a one‑time modification to the flight control leading edge attachments by installing additional locking devices for rudder, ailerons and elevators (Requirement 4).  \n- States that once the modification in Requirement 4 is done, the repetitive inspections and re‑torque requirements (Requirements 1–3) are no longer required (Note 1).\n\n**Who it affects**\n\n- Aircraft operators and owners of the specified Fokker F50 models (Applicability).  \n- Maintenance organisations and licensed aircraft maintenance engineers who must carry out the inspections, corrective actions and the modification following the detailed procedures in the referenced Fokker Service Bulletins (Requirements 1–4 and the referenced SBs).  \n- Parts suppliers and logistics providers who supply the locking devices and any replacement screws or hardware needed to carry out the modification and corrective work.\n\n**Why it matters (safety and operational mechanism)**\n\n- The directive responds to incidents where a leading edge attachment screw came loose and caused elevator binding after landing and to an in‑flight vibration incident associated with a loose elevator leading edge section (Background).  \n- Loose attachment screws can cause control surface binding, which can impair control of the aircraft. The inspections detect and correct screw torque; the modification installs additional locking devices intended to prevent recurrence.\n\n**How compliance works (timing, reference documents, and termination of repetitive checks)**\n\n- Inspections / re‑torque intervals: the AD sets specific timelines for the first inspections and recurring intervals for each control surface (see Compliance paragraphs 1–3). Those intervals are shorter than in earlier versions (Amendment 4).  \n- Modification deadline: the additional‑locking modification must be completed within 24 calendar months after 31 October 2002 or by the aircraft reaching 15 years time‑since‑new, whichever is earlier (Compliance 4).  \n- The detailed step‑by‑step technical procedures to perform the checks, corrective actions and the modifications are contained in the cited Fokker Service Bulletins (each Requirement refers to a specific SB revision and date).  \n- Once the modification is completed per the SBs, the recurring inspections are no longer required (Note 1).\n\n**Who pays, who decides, and what behaviour changes**\n\n- Aircraft operators pay for the inspections, any corrective repairs, the cost of parts and the labour to install the locking devices.  \n- Maintenance providers (organisations or licensed engineers) decide the specific execution timing within the AD windows and perform the work in accordance with the Fokker SBs referenced in the AD.  \n- Operators will either: keep up with the repeated inspection/retorque cycle (continuing recurring maintenance cost and scheduling), or invest once in the locking device modification (up‑front cost and downtime) to eliminate the recurring checks.\n\n**Costs, incentives and trade‑offs**\n\n- Shorter inspection intervals (Amendment 4) increase recurring maintenance cost and aircraft downtime until the terminating modification is completed (Compliance 1–3 and Background).  \n- The terminating modification concentrates a one‑time cost on the operator but removes the ongoing cost and scheduling burden of repetitive checks (Requirement 4 and Note 1).  \n- The AD channels technical implementation through Fokker Service Bulletins; operators must have access to the specified SB revisions and any parts they require. This creates dependence on OEM documentation and parts availability (Requirements reference SB F50-55-007 Rev 2, F50-55-009 Rev 2, F50-57-020 Rev 2, F50-55-010 Rev 2, F50-57-021 Rev 2, F50-55-008 Rev 3).\n\n**Implementation risks and compliance burden**\n\n- Operators must track varying intervals for different surfaces and the 15‑year limit for modification; record‑keeping errors could lead to missed inspections or missed modification deadlines (Compliance section).  \n- Availability of replacement hardware and the specific locking devices could affect how quickly operators can comply; until modification is fitted, aircraft remain subject to the shorter recurring inspection windows.  \n- Enforcement is by the Civil Aviation Safety Authority delegate under the CAR (stated in the preamble); the AD imposes mandatory corrective action where the delegate deems it necessary (preamble wording).\n\n**Provenance and stated purpose**\n\n- The AD cites operator reports of loose screws and in‑flight vibration as the factual triggers for the action (Background). The directive and its amendments progressively broadened inspection scope (from elevator to also cover rudder and aileron), adjusted inspection intervals and added a terminating modification (Background and Amendment history).  \n\n**Practical operator choice**\n\n- Operators trade recurring inspection cost and scheduling complexity against a one‑time modification cost. The AD’s mechanics make modification the clear way to remove ongoing inspection obligations (Note 1)."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":true,"description":"The original AD (September 1999) only addressed elevator leading edge attachment issues. Through Amendments 1–4, the scope expanded significantly: Amendment 1 added rudder and aileron inspections; Amendment 2 adjusted rudder compliance intervals; Amendment 3 introduced permanent modification requirements; and Amendment 4 tightened inspection intervals and added new modification deadlines based on further incident reports. The legislation grew from a single-component inspection to a comprehensive flight control surface safety program."},"complexity_factors":["Multiple amendment history (Amendments 1–4) creating layered requirements","Cross-references to external technical documents (Fokker Service Bulletins) which are not reproduced in the text","Complex compliance timing with multiple alternative triggers ('whichever occurs first' logic)","Interdependent requirements where Requirement 4 terminates Requirements 1–3","Specific model and serial number applicability requiring technical verification"],"plain_english_summary":"This CASA safety order targets Fokker F50 series aeroplanes and requires operators to inspect and torque the screws securing the leading edges of elevators, rudder and ailerons, repeating checks periodically until a mandated permanent locking modification is installed. It affects all Fokker F50 owners/operators because loose screws can jam controls and risk loss of control. Operators were given specified deadlines to start checks and complete the modification."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f50-79-amdt-4-control-surfaces-leading-edge-attachment","history":"/api/acts/ad-f50-79-amdt-4-control-surfaces-leading-edge-attachment/history","analysis":"/api/acts/ad-f50-79-amdt-4-control-surfaces-leading-edge-attachment/analysis","conflicts":"/api/acts/ad-f50-79-amdt-4-control-surfaces-leading-edge-attachment/conflicts","importantCases":"/api/acts/ad-f50-79-amdt-4-control-surfaces-leading-edge-attachment/important-cases","documents":"/api/acts/ad-f50-79-amdt-4-control-surfaces-leading-edge-attachment/documents"}}