{"id":"F2006B09782","name":"AD/F28/48 Amdt 1 - Horizontal Stabilizer Control Unit Cavity Venting","slug":"ad-f28-48-amdt-1-horizontal-stabilizer-control-unit-cavity-venting","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54701,"registerId":"commonwealth-F2006B09782-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F28/48 Amdt 1 - Horizontal Stabilizer Control Unit Cavity Venting","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 F28 Series Aeroplanes\n\nAD/F28/48\n\nAmdt 1\n\n  \nHorizontal Stabilizer Control Unit Cavity Venting 3/86\n\nApplicability: All models with S/Nos. 11003 to 11211, 11213 to 11218, 11222, 11991 and 11992 fitted with Horizontal Stabilizer Control Units P/No. 11100 \\- (all dash numbers below\n\n\\- 39AA) S/Nos \\-001 to \\-386 disregarding all prefixes.\n\nRequirement: Action in accordance with Fokker SB F28/27-161 and subsequent issues, and Menasco SB27-93.\n\nNote 1: Fokker SB F28/27-161 draws the attention of operators to the requirements of Menasco SB27-93.\n\nNote 2: RLD AD 85-36 refers.\n\nCompliance: Before further flight after 30 September 1985.\n\nBackground: Leakage of a clutch piston seal into the cavity between hydraulic systems 1 and 2 can cause increased seal friction which can lead to a decrease in control unit reliability.\n\nTo prevent any hydraulic build up within the cavity the existing closed plugs are replaced with vented plugs. This AD has been amended to remove the prefixes from the Stabilizer Control Unit Serial numbers.\n\nFederal Register of Legislative Instruments F2006B09782","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a narrow, technical airworthiness directive addressing a specific mechanical defect in a specific aircraft type. Amendment 1 made only a minor administrative clarification (removing prefixes from serial numbers) without expanding the scope beyond the original safety purpose."},"complexity_factors":["Highly specific applicability criteria involving multiple serial number ranges and part number ranges with dash number limitations","Cross-references to two separate Service Bulletins (Fokker SB F28/27-161 and Menasco SB27-93) and a Dutch aviation authority directive (RLD AD 85-36)","Technical aviation terminology requiring specialized knowledge (hydraulic systems, clutch piston seals, cavity venting, dash numbers)","Nested conditions: applicability depends on aircraft model AND serial number AND specific part number AND part serial number range"],"plain_english_summary":"This AD mandates replacing sealed plugs with vented (breathing) plugs in the horizontal stabilizer control unit on specified Fokker F28 aircraft and control‑unit serials to prevent hydraulic fluid pressure build‑up between two systems. The change averts seal friction that could render the stabilizer control unreliable and risk loss of pitch control. Compliance was required before the next flight after 30 Sept 1985; Amendment 1 clarified affected serial numbers."},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":true,"description":"The AD was amended to remove prefixes from the Stabilizer Control Unit serial numbers, widening the population of affected units; the mechanical requirement (replace closed plugs with vented plugs per the cited service bulletins) remains unchanged (see 'Applicability' and 'This AD has been amended...' in Background)."},"complexity_factors":["Requires compliance with external service bulletins (Fokker SB F28/27-161; Menasco SB27-93) rather than containing full technical instructions","Applicability defined by part number and a range of serial numbers with an amendment removing prefixes (increases identification work)","Immediate compliance deadline (before further flight after 30 Sept 1985) imposes scheduling/operational constraints","Modification involves parts replacement (closed to vented plugs) with parts identification by dash numbers","Cross-references other ADs and Federal Register entry (RLD AD 85-36; F2006B09782) for context and traceability"],"plain_english_summary":"_This Airworthiness Directive requires replacing closed plugs in the cavity of specified Fokker F28 horizontal stabilizer control units with vented plugs, following Fokker SB F28/27-161 and Menasco SB27-93, to stop hydraulic buildup between systems 1 and 2 (Requirement; Background)._  \n\n_It applies to listed P/No. 11100-series units and serial numbers (prefixes removed), obliges operators to carry out and pay for the work before further flight after 30 Sept 1985, and cross-references RLD AD 85-36 (Applicability; Compliance)._"}},"importantCases":[],"_links":{"self":"/api/acts/ad-f28-48-amdt-1-horizontal-stabilizer-control-unit-cavity-venting","history":"/api/acts/ad-f28-48-amdt-1-horizontal-stabilizer-control-unit-cavity-venting/history","analysis":"/api/acts/ad-f28-48-amdt-1-horizontal-stabilizer-control-unit-cavity-venting/analysis","conflicts":"/api/acts/ad-f28-48-amdt-1-horizontal-stabilizer-control-unit-cavity-venting/conflicts","importantCases":"/api/acts/ad-f28-48-amdt-1-horizontal-stabilizer-control-unit-cavity-venting/important-cases","documents":"/api/acts/ad-f28-48-amdt-1-horizontal-stabilizer-control-unit-cavity-venting/documents"}}