{"id":"F2006B02480","name":"AD/AS 355/25 - MGB Suspension Bars","slug":"ad-as-355-25-mgb-suspension-bars","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41736,"registerId":"commonwealth-F2006B02480-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AS 355/25 - MGB Suspension Bars","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)  \nEurocopter AS 355 (Twin Ecureuil) Series Helicopters\n\nAD/AS 355/25 MGB Suspension Bars 6/87 DM\n\nApplicability: All models AS 355E, F, F1 and F2.\n\nRequirement: Action in accordance with Aerospatiale SB NO 05.16.\n\nNote: Bureau Veritas AD T87-038-032(B) refers.\n\nCompliance: Within 25 hours time in service after 3 April 1987 and thereafter at each daily inspection.\n\nNote: The daily inspection may be accomplished by the pilot-in-command, in which case the precise AD reference shall be entered in a certification made on the Maintenance Release coincident with that for the daily inspection. A copy of the Reference Document is to be carried in the aircraft.\n\nBackground: The manufacturer has had reports including Australian MDR’s of the MGB suspension bar end bearings being displaced in the tube ends.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The AD applies to the specified AS 355 variants and prescribes inspection actions and timing. Nothing in the text indicates a change from an earlier or different original scope; the instrument sets an initial inspection window and an ongoing daily inspection requirement for those models (Applicability; Compliance)."},"complexity_factors":["Narrow applicability (only AS 355E/F/F1/F2 models) reduces scope complexity.","Short, prescriptive compliance timing (initial 25 hours TIS, then daily) is simple to operationalise but creates high frequency of required action.","Dependence on an external technical document (Aerospatiale SB NO 05.16) requires access to and interpretation of manufacturer guidance.","Administrative detail allowing pilot-in-command to perform inspections adds procedural complexity (certification on Maintenance Release and carrying the reference document).","Cross-reference to another AD (Bureau Veritas AD T87-038-032(B)) adds a minor additional compliance linkage."],"plain_english_summary":"What this instrument changes mechanically\n\n- It requires specific inspection action for the main gearbox (MGB) suspension bar end bearings on certain Eurocopter AS 355 helicopter models. The mandatory action is to be carried out \"in accordance with Aerospatiale SB NO 05.16.\" (Requirement)\n\nWho is affected\n\n- Owners, operators and pilots of Eurocopter AS 355E, AS 355F, AS 355F1 and AS 355F2 helicopters (Applicability).\n\nWhat must be done and by whom\n\n- An inspection must be performed within 25 hours time-in-service after 3 April 1987 and then at every daily inspection thereafter (Compliance).\n- The daily inspection may be carried out by the pilot-in-command. If the pilot performs it, the exact AD reference must be entered on the aircraft's Maintenance Release at the same time as the daily inspection certification, and a copy of the referenced service document must be kept on board (Note under Compliance).\n- The mandated inspection procedure is the one specified in the manufacturer’s Service Bulletin (Aerospatiale SB NO 05.16) (Requirement). The AD also notes a related Bureau Veritas airworthiness directive (Note under Requirement).\n\nWhy the AD was issued (source statement)\n\n- The stated reason is that the manufacturer reported incidents, including Australian Mandatory Defect Reports, of MGB suspension bar end bearings being displaced in the tube ends (Background).\n\nPractical effects, incentives and costs (mechanics, not judgement)\n\n- Who pays: aircraft operators (owners or lessees) bear the direct costs of carrying out the initial inspection and the recurring daily inspections, including any follow-up maintenance if the SB identifies defects (Requirement; Compliance).\n- Who decides: the Civil Aviation Safety Authority issues the AD; the operator or maintenance provider decides how to resource and schedule the inspections, subject to the AD timing (Applicability; Compliance). A pilot-in-command may perform the daily inspection and certify it, shifting performance and record-keeping to flight crew when they choose to do so (Note under Compliance).\n- Compliance burden and administrative steps: operators must (a) obtain and follow Aerospatiale SB NO 05.16, (b) perform the initial check within 25 hours TIS and repeated daily checks, (c) keep a copy of the reference document on the helicopter, and (d) record the AD reference on the Maintenance Release when a pilot carries out the inspection (Requirement; Compliance; Note).\n- Implementation risk and substitution effects: the AD mandates inspection frequency rather than a specific replacement schedule; operators may choose to increase maintenance action beyond the AD if the service bulletin requires it. Allowing pilots to perform the daily inspection reallocates some inspection workload from maintenance organisations to flight crew; that changes who is responsible for detection and record entry but does not change the AD’s substantive inspection requirement (Compliance; Note).\n- Reliance on external technical material: the AD makes compliance contingent on following a manufacturer-issued service bulletin (Aerospatiale SB NO 05.16) and references another AD from Bureau Veritas; operators must have access to and follow those documents to meet the AD (Requirement; Note).\n\nTrade-offs and implementation considerations\n\n- The AD imposes a recurring inspection duty that can be met by pilots or maintenance personnel; this can lower short-term maintenance labour costs if pilots perform inspections, but shifts record-keeping and responsibility to flight crew (Compliance; Note).\n- The AD’s geographic and model applicability is narrow (specific AS 355 variants) and the procedure is externalised to a manufacturer service bulletin. That concentrates direct compliance costs on a defined group of operators and concentrates the technical-specification reliance on the manufacturer’s document (Applicability; Requirement).\n\nSource citations\n\n- Applicability: \"All models AS 355E, F, F1 and F2.\" (Applicability)\n- Requirement: \"Action in accordance with Aerospatiale SB NO 05.16.\" (Requirement)\n- Compliance: \"Within 25 hours time in service after 3 April 1987 and thereafter at each daily inspection.\" (Compliance)\n- Pilot inspection and documentation: \"The daily inspection may be accomplished by the pilot-in-command ... the precise AD reference shall be entered in a certification made on the Maintenance Release ... A copy of the Reference Document is to be carried in the aircraft.\" (Note under Compliance)\n- Background: \"The manufacturer has had reports including Australian MDR’s of the MGB suspension bar end bearings being displaced in the tube ends.\" (Background)\n"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a discrete, single-issue airworthiness directive addressing a specific mechanical defect in a specific aircraft type. It has not expanded beyond its original safety purpose."},"complexity_factors":["Single technical requirement referencing an external document (Aerospatiale SB NO 05.16) rather than spelling out the procedure","Simple applicability clause covering four specific model variants","Straightforward compliance timeline (25 hours + recurring daily)","One conditional provision regarding pilot-performed inspections and associated paperwork requirements","Minimal defined terms (only standard aviation acronyms like MGB, TIS)","No nested exceptions or complex cross-referencing beyond a single note referencing a French regulatory equivalent (Bureau Veritas AD)"],"plain_english_summary":"**What this is:** This is an Airworthiness Directive (AD) — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for specific helicopters.\n\n**Which aircraft:** All Eurocopter AS 355 series helicopters (models E, F, F1, and F2), also known as the \"Twin Ecureuil.\"\n\n**The safety problem:** The manufacturer received reports (including from Australia) that the bearings at the ends of the Main Gearbox (MGB) suspension bars were slipping out of their tubes. This is a serious mechanical fault that could affect flight safety.\n\n**What must be done:**\n- **Follow the manufacturer's Service Bulletin:** Operators must comply with Aerospatiale Service Bulletin No. 05.16 (this document contains the technical instructions for inspection and repair).\n- **When:** First inspection within 25 flight hours after 3 April 1987, then **every day the aircraft flies** (at each daily inspection).\n- **Who can do it:** The daily inspection can actually be done by the pilot-in-command (the pilot flying the aircraft), rather than requiring a licensed aircraft mechanic.\n- **Paperwork:** If the pilot does the check, they must write the specific Airworthiness Directive reference number (AD/AS 355/25) on the Maintenance Release (the aircraft's official logbook) at the same time they sign off the daily inspection. Also, a copy of the reference document (the Service Bulletin) must be kept on board the aircraft.\n\n**Why it matters:** This directive prevents potential catastrophic failure of the helicopter's main gearbox mounting system. The repetitive daily inspection requirement reflects the serious nature of the defect and the need for constant vigilance."}},"importantCases":[],"_links":{"self":"/api/acts/ad-as-355-25-mgb-suspension-bars","history":"/api/acts/ad-as-355-25-mgb-suspension-bars/history","analysis":"/api/acts/ad-as-355-25-mgb-suspension-bars/analysis","conflicts":"/api/acts/ad-as-355-25-mgb-suspension-bars/conflicts","importantCases":"/api/acts/ad-as-355-25-mgb-suspension-bars/important-cases","documents":"/api/acts/ad-as-355-25-mgb-suspension-bars/documents"}}