{"id":"F2006B02487","name":"AD/AS 355/33 Amdt 1 - Tail Rotor Front Drive Shaft","slug":"ad-as-355-33-amdt-1-tail-rotor-front-drive-shaft","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41743,"registerId":"commonwealth-F2006B02487-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AS 355/33 Amdt 1 - Tail Rotor Front Drive Shaft","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 355/33\n\nAmdt 1\n\n  \nTail Rotor Front Drive Shaft 5/89\n\nApplicability: All model AS 355 fitted with forward drive shaft P/N 355A34-1037-00. Requirement: Action in accordance with Aerospatiale Service Bulletin No 05-20 Revision 2.\n\nCompliance: 1. Within 50 hours TIS after 7 December 1988 or by 31 December 1988, whichever occurs first. Thereafter, reinspect at intervals not exceeding 100 hours time in service.\n\n    2. Before removal and after installation of the following components:\n\n    \\- forward drive shaft elements,\n\n    \\- oil cooler,\n\n    \\- fan,\n\n    \\- oil cooler or fan support.\n\n    3. If abnormal vibration is noted in the fan assembly,\n\n    4. If a crack is found on one of the oil cooler or fan supports.\n\nBackground: The manufacturer has advised of a forward drive shaft failure caused by excessive unbalance of a main gearbox oil cooler fan assembly. A further revision of the requirement document requires the compliance requirements to be expanded.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"The AD expands the original requirement document by broadening compliance actions: it adds recurring inspections at ≤100‑hour intervals and explicit inspection triggers tied to component removal/installation, abnormal vibration, and discovered cracks, per the revised service bulletin."},"complexity_factors":["Reference to an external technical document (Aerospatiale Service Bulletin No 05-20 Rev 2) that operators must obtain and follow","Multiple time-based compliance triggers (initial: within 50 hours TIS or by a calendar date; recurrent: every ≤100 hours TIS)","Conditional inspection triggers (before removal and after installation of specified components; on abnormal vibration; on discovery of cracks)","Specific applicability limited to AS 355 helicopters fitted with forward drive shaft P/N 355A34-1037-00","Regulatory formality (issued under Civil Aviation Regulations Part 39 as an Airworthiness Directive)"],"plain_english_summary":"This airworthiness directive requires operators of Eurocopter AS 355 helicopters fitted with forward drive shaft P/N 355A34-1037-00 to follow Aerospatiale Service Bulletin No 05-20 Rev 2. It imposes an initial inspection within a short hours-or-date window, recurring inspections at set intervals, and inspections tied to removal/installation or evidence of vibration or cracking. The Civil Aviation Safety Authority mandates compliance; operators pay for the additional inspections and must change maintenance scheduling to address a risk from an unbalanced oil‑cooler fan assembly."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is Amendment 1 to an existing Airworthiness Directive. The amendment expands compliance requirements based on a revised manufacturer service bulletin, but remains tightly focused on the original safety issue (drive shaft failure due to fan unbalance). The scope has not grown beyond the specific mechanical defect it was designed to address."},"complexity_factors":["Single discrete safety issue addressed (one helicopter model, one specific part)","Only 4 defined compliance triggers (time-based, maintenance event, vibration symptom, crack detection)","No nested exceptions or conditional logic — requirements are straightforward 'if X, then inspect'","Short document (approximately 200 words)","Single cross-reference to manufacturer service bulletin (Aerospatiale Service Bulletin No 05-20 Revision 2)","Clear applicability criteria (specific part number)"],"plain_english_summary":"This AD requires operators of Eurocopter AS355 helicopters fitted with forward drive shaft P/N 355A34-1037-00 to inspect the tail-rotor front drive shaft because an unbalanced oil cooler fan can cause shaft failure. An initial inspection is required within 50 flight hours (or by 31 Dec 1988) and then every 100 flight hours; extra inspections follow removal/installation of the shaft/cooler/fan/supports, abnormal fan vibration, or discovered cracks.\n\nThe inspections aim to prevent loss of tail-rotor control and potential catastrophic accidents by catching damage early."}},"importantCases":[],"_links":{"self":"/api/acts/ad-as-355-33-amdt-1-tail-rotor-front-drive-shaft","history":"/api/acts/ad-as-355-33-amdt-1-tail-rotor-front-drive-shaft/history","analysis":"/api/acts/ad-as-355-33-amdt-1-tail-rotor-front-drive-shaft/analysis","conflicts":"/api/acts/ad-as-355-33-amdt-1-tail-rotor-front-drive-shaft/conflicts","importantCases":"/api/acts/ad-as-355-33-amdt-1-tail-rotor-front-drive-shaft/important-cases","documents":"/api/acts/ad-as-355-33-amdt-1-tail-rotor-front-drive-shaft/documents"}}