{"id":"F2006B02492","name":"AD/AS 355/38 - Tail Rotor Drive Shaft Bearings","slug":"ad-as-355-38-tail-rotor-drive-shaft-bearings","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41748,"registerId":"commonwealth-F2006B02492-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AS 355/38 - Tail Rotor Drive Shaft Bearings","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 355/38 Tail Rotor Drive Shaft Bearings 11/91\n\nDM\n\nApplicability: All AS 355 helicopters versions E, F, F1, F2 and N equipped with P/N P.9107.NPP7 FAFNIR tail rotor drive shaft bearings not marked with an “X” on the seal flange.\n\nRequirement: Action in accordance with the Technical Requirements of DGAC AD 91-158-044 (B) for all aircraft acceptance tested by Aerospatiale Marignane between 15 May 1991 and 20 July 1991 or prior to 15 May 1991 and have operated less than 100 hours time in service.\n\nNote: Aerospatiale Telex Service No. 01-35 refers.\n\nCompliance: By 30 August 1991 or prior to issue of Australian C of A, whichever occurs first. Background: Corroded bearings which could seize may have been fitted to the tail rotor drive shaft.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive's scope is limited and specific: it applies only to AS 355 E/F/F1/F2/N helicopters fitted with P/N P.9107.NPP7 FAFNIR tail rotor drive shaft bearings not marked with an \"X\" and further limited by acceptance-test dates or accumulated hours (Applicability; Requirement). There is no indication in the text that the directive broadens or narrows its own applicability beyond those stated criteria, so the scope has not changed from the described intent in the AD."},"complexity_factors":["Narrow, well-defined applicability tied to part number and a visible mark on the seal flange (Applicability).","Compliance requires following a separate foreign airworthiness directive (DGAC AD 91-158-044 (B)), adding a cross-reference dependency (Requirement).","Applicability further restricted by aircraft acceptance-test date ranges and an hours-in-service threshold, creating multi-factor eligibility (Requirement).","Fixed compliance timing (calendar date or prior to issue of Australian C of A) creates operational scheduling pressure (Compliance).","Technical detail delegated to an Aerospatiale telex, so implementers must access external technical documentation (Note)."],"plain_english_summary":"This AD requires operators of certain Eurocopter AS 355 E/F/F1/F2/N helicopters with bearing P/N P.9107.NPP7 FAFNIR (without an \"X\" on the seal flange) to inspect and, if needed, replace tail-rotor drive-shaft bearings because corrosion could cause seizure. It affects owners/operators and maintenance providers by imposing inspection/repair actions (per referenced DGAC/Aerospatiale guidance), potential grounding or C of A delays, and the direct costs and logistical burdens of compliance."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-limited safety directive addressing a specific manufacturing defect in a specific helicopter model. It has not expanded beyond its original purpose of grounding/inspecting aircraft with potentially defective bearings."},"complexity_factors":["Very short document (approximately 150 words)","Only 2 defined applicability criteria (manufacture date range OR pre-May 1991 with low hours)","Single technical reference to external French aviation authority document (DGAC AD 91-158-044 (B))","No nested exceptions or conditional logic beyond the two-part applicability test","Clear, single compliance deadline","No cross-references to other Australian legislation beyond basic mention of Civil Aviation Regulations 1998 Part 39"],"plain_english_summary":"**What this is:** This is an **Airworthiness Directive (AD)** — essentially a mandatory safety notice issued by Australia's Civil Aviation Safety Authority (CASA). Think of it like a compulsory recall notice for aircraft, but with legal force.\n\n**What it does:** It orders owners and operators of specific Eurocopter AS 355 helicopters (nicknamed \"Twin Ecureuil\") to inspect or replace certain tail rotor drive shaft bearings. These bearings (part number P.9107.NPP7 FAFNIR) were made without a special \"X\" mark on the seal flange and could be corroded. Corroded bearings can seize up (freeze solid), which would cause the tail rotor to stop working — a catastrophic failure that could make the helicopter crash.\n\n**Who it affects:** \n- **Aircraft:** All AS 355 model helicopters (versions E, F, F1, F2, and N) that have these specific bearings installed\n- **Specific timeframe:** Only helicopters that were factory-tested by Aerospatiale Marignane between 15 May 1991 and 20 July 1991, OR tested before 15 May 1991 but with less than 100 hours of flight time\n- **Operators:** Anyone flying these helicopters in Australia must comply before getting their Australian Certificate of Airworthiness (like a registration safety certificate)\n\n**What must be done:** Follow the technical instructions in a French aviation safety document (DGAC AD 91-158-044 (B)) to check or fix the bearings.\n\n**Deadline:** 30 August 1991, or before the helicopter gets its Australian safety certificate — whichever comes first.\n\n**Why it matters:** This is a **critical safety fix**. The tail rotor keeps the helicopter from spinning uncontrollably. If the bearing seizes due to corrosion, the pilot could lose control and crash. The directive forces immediate action before the aircraft can legally fly in Australia."}},"importantCases":[],"_links":{"self":"/api/acts/ad-as-355-38-tail-rotor-drive-shaft-bearings","history":"/api/acts/ad-as-355-38-tail-rotor-drive-shaft-bearings/history","analysis":"/api/acts/ad-as-355-38-tail-rotor-drive-shaft-bearings/analysis","conflicts":"/api/acts/ad-as-355-38-tail-rotor-drive-shaft-bearings/conflicts","importantCases":"/api/acts/ad-as-355-38-tail-rotor-drive-shaft-bearings/important-cases","documents":"/api/acts/ad-as-355-38-tail-rotor-drive-shaft-bearings/documents"}}