{"id":"F2006B09591","name":"AD/ENST 28/34 - Main Rotor Shaft","slug":"ad-enst-28-34-main-rotor-shaft","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54300,"registerId":"commonwealth-F2006B09591-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/ENST 28/34 - Main Rotor 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)  \nEnstrom F-28 Series Helicopters\n\nAD/ENST 28/34 Main Rotor Shaft 10/93 TX\n\nApplicability: Models F-28A, F-28C, F-28C2, F-28F, 280, 280C, 280F, and 280FX equipped with composite-wrapped main rotor shaft, part number 28-13183.\n\nRequirement: 1. Inspect the main rotor shaft in accordance with Enstrom Service Directive Bulletin No. 0083, dated 16 July 1993. If the shaft is found with separations in the composite wrappings, corrosion, red-coloured residue or cracks, retire the shaft from service and replace with main rotor shaft part number 28-13140-11 or 28- 13104-1.\n\n2. Retire the main rotor shaft from service and replace with main rotor shaft part number 28-13140-11 or 28-13104-1.\n\nNote: FAA Priority Letter AD 93-15-10, issued 3 August 1993, refers.\n\nCompliance: 1. Inspect the main rotor shaft before further flight after 6 August 1993.\n\n2. Retire the main rotor shaft not later than 10 hours component time in service after 6 August 1993, but immediately if main rotor vibrations develop which cannot be corrected by normal track and balance procedures, or if the vibrations return soon after correction.\n\nBackground: This AD is prompted by a report of a large crack in a composite- wrapped main rotor shaft. The crack was immediately below the upper radius and was concealed by the composite wrap. Main rotor track and balance problems that arise suddenly, or those that do not respond to normal corrective actions, could be caused by a cracked shaft. This condition, if not corrected, could result in failure of the shaft, loss of the main rotor, and subsequent loss of control of the helicopter.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"The directive addresses a specific, reported defect in the composite-wrapped main rotor shaft for listed F‑28 variants and mandates inspection and replacement of that part. It does not broaden applicability beyond the stated models and part number or add unrelated regulatory obligations; it implements corrective action limited to the identified component and its direct operational consequences."},"complexity_factors":["Narrow applicability to specific models and a single composite-wrapped part number (Applicability).","Two distinct compliance actions with tight timing: an immediate inspection requirement and mandatory retirement within 10 hours after 6 August 1993 (Requirement; Compliance).","Conditional immediate retirement trigger based on persistent or recurrent main-rotor vibrations (Compliance).","Mandatory replacement limited to two specified part numbers, creating a procurement constraint for operators (Requirement).","Dependence on an external service bulletin for inspection procedures and a referenced FAA Priority Letter AD (Requirement; Note).","Inspection difficulty due to concealed cracks under composite wrap, increasing detection risk and technical inspection burden (Background).","Short compliance window and potential for immediate grounding impose operational disruption and cost on owners/operators (Compliance)."],"plain_english_summary":"This Airworthiness Directive requires operators of specified Enstrom F‑28 helicopters fitted with the composite‑wrapped main rotor shaft P/N 28‑13183 to inspect that shaft using Enstrom Service Directive Bulletin No. 0083 and to retire and replace it with P/N 28‑13140‑11 or 28‑13104‑1. Inspections must occur before the next flight after 6 August 1993, and the shaft must be removed within 10 hours of service after that date—or immediately if main rotor vibrations persist or recur."},"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"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a targeted safety directive addressing a specific mechanical defect in a specific helicopter part. It has not expanded beyond its original purpose of mandating inspection and replacement of defective main rotor shafts."},"complexity_factors":["Single, specific mechanical component targeted (main rotor shaft)","Only 2 compliance requirements with clear deadlines","Limited applicability (8 specific helicopter models, 1 part number)","No nested exceptions or conditional logic beyond standard aviation safety triggers (vibration warnings)","Short document with minimal cross-referencing (only references one FAA directive and one manufacturer bulletin)","Plain language background section explaining the safety rationale"],"plain_english_summary":"This CASA Airworthiness Directive applies to specified Enstrom helicopter models fitted with composite-wrapped main rotor shaft P/N 28-13183 and requires immediate inspection before further flight (per Enstrom Service Directive Bulletin No. 0083) following discovery of a crack hidden under the wrap.  \n\nEven if the shaft passes inspection, it must be replaced with an approved part within 10 flight hours after 6 August 1993, and must be replaced immediately if wrapping separation, corrosion, red residue, cracks, or unresolved vibration are found."}},"importantCases":[],"_links":{"self":"/api/acts/ad-enst-28-34-main-rotor-shaft","history":"/api/acts/ad-enst-28-34-main-rotor-shaft/history","analysis":"/api/acts/ad-enst-28-34-main-rotor-shaft/analysis","conflicts":"/api/acts/ad-enst-28-34-main-rotor-shaft/conflicts","importantCases":"/api/acts/ad-enst-28-34-main-rotor-shaft/important-cases","documents":"/api/acts/ad-enst-28-34-main-rotor-shaft/documents"}}