{"id":"F2006B09886","name":"AD/F50/58 Amdt 4 - MLG Sliding Member Out-Stop Assembly","slug":"ad-f50-58-amdt-4-mlg-sliding-member-out-stop-assembly","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":55021,"registerId":"commonwealth-F2006B09886-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F50/58 Amdt 4 - MLG Sliding Member Out-Stop Assembly","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nFokker F50 (F27 Mk 50) Series Aeroplanes\n\nAD/F50/58\n\nAmdt 4\n\n  \nMLG Sliding Member Out-Stop Assembly 6/98\n\nApplicability: All model F27 Mk 50 aircraft, all serial numbers, equipped with Dowty Aerospace MLG legs P/N 201017001, 201017002 and P/N 201020001 not incorporating Dowty Aerospace SB F50-32-27 R4.\n\nRequirement: 1. Inspect all main landing gear legs for correct installation in accordance with Part A of Messier Dowty SB F50-32-48 R4 dated June 21, 1995.\n\nNote: Fokker SB F50-32-025 dated September 23, 1992 also refers.\n\n    2. Inspect and measure the extension of each sliding member when the landing gear is fully extended in accordance with Part B of Messier Dowty SB F50-32-48 R4 dated June 21, 1995.\n\n    3. If while inspecting the MLG in accordance with Requirements (1) or (2) parts are found missing or damaged, action in accordance with Dowty Aerospace SB F50-32-27 R2 or SB F50-32-49, as applicable.\n\nNote: MLG legs previously modified in accordance with Dowty Aerospace SB F50- 32-27 R2 and R3 are exempt from the inspections of Requirement 1 and 2 .\n\n    4. Modify main landing gear leg in accordance with Dowty Aerospace SB F50-32-27 R4 dated December 18, 1992.\n\nNote: RLD AD 1996-159 (A) dated December 31, 1996, supersedes and cancels RLD AD 92-118/3 (A).\n\nCompliance: 1. Unless previously carried out, within 30 days from 27 March 1997.\n\n    2. Unless previously carried out, within 30 days from 27 March 1997. Thereafter reinspect at intervals not exceeding 500 flight cycles until requirement 4 has been complied with.\n\n    3. Before further flight.\n\n    4. Unless previously carried out, within 5000 flight cycles or 30 calendar months, whichever occurs first, after 27 March 1997.\n\nThis Amendment becomes effective on 21 May 1998.\n\nBackground: A report was received of an accident during landing in which an F50 aircraft left the runway sideways and was severely damaged. This event has been attributed to a MLG sliding member inadvertently overextending and allowing the torque links to move to an overcentre position, with the subsequent failure of the torque link centre joint pin.\n\nAmendment 1 was issued in response to a new RLD AD which advised that modification is now accepted as a terminating action for the current inspection.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\nAmendment 2 was issued to reflect the latest issue of the Requirement Document which list the affected MLG serial numbers, and introduces an alternative terminating action for an inspection requirement.\n\nAmendment 3 was raised on receipt of RLD AD 1996-159 (A) dated December 31, 1996, which mandates terminating action.\n\nThis amendment being raised to rectify Service Bulletin numbers referred to in Amendment 3.\n\nAmendment 3 of this Airworthiness Directive became effective on 27 March 1997 Amendment 2 of this Airworthiness Directive became effective on 31 March 1994\\. Amendment 1 of this Airworthiness Directive became effective on 4 April 1993.\n\nThe original issue of this Airworthiness Directive became effective on 7 February 1993.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":true,"description":"The Directive’s scope evolved through amendments: initially imposing inspections and corrective actions, later accepting a Dowty modification as a terminating action, adding an alternative terminating action and specifying affected MLG serial numbers, and correcting service bulletin references. These changes narrowed operational burden over time by allowing modification as an end-state while adding detailed serial-number applicability and procedural clarifications."},"complexity_factors":["Multiple technical actions: inspect installation, measure extension, immediate repairs for missing/damaged parts, and a modification as terminating action (Requirements 1–4).","References several external service bulletins (Dowty SB F50-32-48 R4; SB F50-32-27 R2/R3/R4; SB F50-32-49) and a Fokker SB, requiring operators to follow manufacturer documents.","Applicability limited to specific aircraft models and specified Dowty MLG part numbers, with exemptions for legs already modified (Applicability; Note).","Staggered compliance timelines and recurring inspections: 30-day initial inspections, 500 flight-cycle reinspection intervals until modification, and up to 5000 cycles or 30 months for terminating modification (Compliance).","Amendment history and cross-references to RLD ADs and previous amendments require readers to track superseded and current service bulletin numbers.","Operational impact: immediate 'before further flight' corrective action for discovered damage creates urgent logistical and maintenance burdens on operators and maintenance organisations."],"plain_english_summary":"Mechanically, this Airworthiness Directive requires operators of Fokker F50 (F27 Mk 50) aeroplanes fitted with specified Dowty main landing gear legs to inspect and measure the MLG sliding member/out-stop assembly, repair or replace missing or damaged parts before further flight, and ultimately install a Dowty modification that ends recurring inspections. The Directive targets those aircraft because an accident was attributed to sliding-member overextension; it imposes short inspection deadlines, recurring checks until modification, and a longer-term compliance window for the terminating modification."},"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 legislation maintains its original scope. Amendment 4 is purely administrative — it corrects Service Bulletin reference numbers that were erroneous in Amendment 3. The substantive safety requirements (inspections, measurements, modifications, and compliance timeframes) remain unchanged from the original 1993 directive. The scope has not expanded beyond the specific Fokker F50 landing gear safety issue."},"complexity_factors":["Multiple cross-references to external technical documents (Service Bulletins F50-32-48 R4, F50-32-27 R2/R3/R4, F50-32-49, and Fokker SB F50-32-025)","Nested conditional logic: exemptions apply if previous modifications done (\"MLG legs previously modified... are exempt\")","Multiple compliance deadlines with different triggers (calendar days vs flight cycles vs calendar months)","Four distinct requirements with interdependencies (inspections must continue until modification completed)","Historical amendment trail (4 amendments) creating layered context that must be understood for full compliance","Specific part number applicability filtering (three specific Dowty Aerospace P/Ns)"],"plain_english_summary":"This Airworthiness Directive mandates inspection and a permanent design modification to the main landing gear on certain Fokker F50 aircraft after failures of the sliding member out-stop led to an accident. It affects Fokker F50 operators and maintenance providers and aims to prevent overextension and runway departures.\n\nAmendment 4 only corrects reference numbers to technical service bulletins; it does not change the safety requirements."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f50-58-amdt-4-mlg-sliding-member-out-stop-assembly","history":"/api/acts/ad-f50-58-amdt-4-mlg-sliding-member-out-stop-assembly/history","analysis":"/api/acts/ad-f50-58-amdt-4-mlg-sliding-member-out-stop-assembly/analysis","conflicts":"/api/acts/ad-f50-58-amdt-4-mlg-sliding-member-out-stop-assembly/conflicts","importantCases":"/api/acts/ad-f50-58-amdt-4-mlg-sliding-member-out-stop-assembly/important-cases","documents":"/api/acts/ad-f50-58-amdt-4-mlg-sliding-member-out-stop-assembly/documents"}}