{"id":"F2006B04712","name":"AD/BELL 47/90 - Hydraulic Servo Cylinders","slug":"ad-bell-47-90-hydraulic-servo-cylinders","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44476,"registerId":"commonwealth-F2006B04712-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BELL 47/90 - Hydraulic Servo Cylinders","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)  \nBell Helicopter Textron 47 (All Variants) Series Helicopters\n\nAD/BELL 47/90 Hydraulic Servo Cylinders 1/84\n\nApplicability: All Bell 47 models equipped with hydraulic servo cylinders part number 103650-3, 103650-5 and 47-691-273-1.\n\nRequirement: Part 1: (a) Gain access to hydraulic servo cylinders.\n\n    (b) Inspect for corrosion and verify freedom of input lever pivot bolts by rotating each by hand. If stiffness or binding is felt, spray bolts with WD- 40 or equivalent.\n\n    (c) If condition persists, remove servo from service and return to overhaul facility for repair, upgrade and/or overhaul as required.\n\nPart 2: Inspect and if necessary modify, each servo in accordance with Flight Accessory Services, Service Bulletin 004 Part A.\n\nNote 1: Part 2 does not apply to servo part number 47-691-273-1.\n\nNote 2: Bell Alert SB 47-83-9 and Flight Accessory Services SB 004 refer.\n\nCompliance: Part 1: At the next daily inspection after 28 November 1983 and each daily inspection thereafter. For aircraft maintained in accordance with ANO 100.5.1 this Directive shall be entered on the Maintenance Release as maintenance required. The inspection Part 1 Para (a) and (b) may be performed by the pilot in command, in which case certification is not required. In all other cases certification may be made on the Maintenance Release. This inspection may also be performed and certified by any Licensed Aircraft Maintenance Engineer.\n\nPart 2: Within the next 100 hours time in service after 28 November 1983 but no later than 31 March 1984.\n\nBackground: The manufacturer advises a recent failure of the servo valve input rod assembly, due to corrosion and binding within the assembly linkage and has recommended the above inspection to eliminate this condition.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific mechanical defect in identified helicopter models. It has not expanded beyond its original purpose of addressing the corroded servo cylinder issue identified by the manufacturer."},"complexity_factors":["Multiple part numbers in applicability create conditional coverage","Two distinct compliance regimes (Part 1 ongoing vs Part 2 one-time deadline)","Nested exception: Part 2 does not apply to one specific part number (47-691-273-1)","Dual performer pathway: pilot-performed inspection without certification vs engineer-performed with certification","Cross-references to external documents (Bell Alert SB 47-83-9, Flight Accessory Services SB 004) that are not reproduced in the directive","Date-based and flight hours-based compliance triggers (28 November 1983, 100 hours TIS, 31 March 1984)"],"plain_english_summary":"This CASA Airworthiness Directive mandates inspections and corrective action on hydraulic servo cylinders of Bell 47 helicopters fitted with part numbers 103650-3, 103650-5, and 47-691-273-1 after corrosion was found to cause binding and potential loss of control. It requires daily checks (pilots may perform a basic check) and a one‑time modification/inspection by licensed engineers within the specified compliance window.\n\nIt affects Bell 47 owners/operators, LAMEs, and pilots and aims to prevent in‑flight servo failures."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive limits action to Bell 47 helicopters with the listed servo part numbers and prescribes inspection, remedial removal/overhaul, and modification timelines. It does not broaden scope to other components or aircraft types; it implements the original safety objective to address corrosion and binding in the specified servo assemblies."},"complexity_factors":["Technical specificity: directive applies only to three exact part numbers (PNs).","Two-part compliance regime: immediate recurring daily inspection (Part 1) and a later modification requirement (Part 2).","Exception handling: one listed PN is excluded from Part 2, adding a conditional branch.","Multiple authorised certifiers: pilot-in-command may perform/certify daily checks, otherwise Licensed Aircraft Maintenance Engineer or maintenance release required.","Dependency on external documents: compliance with referenced service bulletins and overhaul actions (Bell Alert SB 47-83-9; Flight Accessory Services SB 004).","Operational timing constraints: daily inspection frequency and a hard modification compliance window (100 hours or specific calendar date)."],"plain_english_summary":"This airworthiness directive requires Bell 47 helicopters fitted with hydraulic servo cylinders (PNs 103650-3, 103650-5, 47-691-273-1) to have the servos checked for corrosion and binding, to free or remove/overhaul any units that stick, and for most units to be modified per a service bulletin within a set flight-hours window. Owners/operators pay for inspections and repairs; pilots may perform and certify the daily check or a licensed engineer may certify. The rule changes routine maintenance actions and timing for the specified parts."},"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-bell-47-90-hydraulic-servo-cylinders","history":"/api/acts/ad-bell-47-90-hydraulic-servo-cylinders/history","analysis":"/api/acts/ad-bell-47-90-hydraulic-servo-cylinders/analysis","conflicts":"/api/acts/ad-bell-47-90-hydraulic-servo-cylinders/conflicts","importantCases":"/api/acts/ad-bell-47-90-hydraulic-servo-cylinders/important-cases","documents":"/api/acts/ad-bell-47-90-hydraulic-servo-cylinders/documents"}}