{"id":"F2006B09599","name":"AD/ENST 28/9 Amdt 4 - Main Rotor Mast","slug":"ad-enst-28-9-amdt-4-main-rotor-mast","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54323,"registerId":"commonwealth-F2006B09599-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Enstrom F-28 Series Helicopters","sectionType":"part","heading":"Enstrom F-28 Series Helicopters","content":"# Enstrom F-28 Series Helicopters\n\nAD/ENST 28/9 Amdt 4 (continued)\n\n    (c) If the transmission is part number 28-13101-1 or \\-1-R, or part number 28- 13101-3 or \\-3-R:\n    (i) Dye-penetrant inspect the shaft upper fillet for a crack, a nick, or a scratch.\n\n    (ii) Polish out nicks or scratches less than 0.005- inch deep.\n\n    (iii) If the shaft is cracked or has a nick or scratch 0.005- inch or more deep, replace the transmission with a serviceable transmission having a large radius shaft fillet before further flight.\n    (d) Replace transmission, part number 28-13101-1 or \\-1-R, or 28-13101-3 or \\-3- R with a serviceable transmission having a large radius shaft fillet.\n\nNote 1: Installing a serviceable transmission with a shaft, part number 28-13104-1 or -1-R, Revision K, L, M, N, P, R, or S, or part number 28-13140-1 or -1-R, is terminating action for the requirements of this Directive.\n\nNote 2: FAA AD 2002-08-03 Amdt 39-12710 refers.\n\nCompliance: 1. Before further flight after 28 August 2002, unless already accomplished.\n\n    2. Before further flight after 28 August 2002, unless already accomplished.\n\n    3. a. Before further flight after 28 August 2002, unless already accomplished.\n\n    b. Unless the initial inspection is already accomplished, before further flight after 28 August 2002. Thereafter at intervals not to exceed 25 hours time in\n\nservice.\n\n    c. Unless the initial inspection is already accomplished, within 5 hours time in service after 28 August 2002. Thereafter at intervals not to exceed 100 hours time in service.\n    d. Unless already accomplished, within 300 hours time in service after 28 August 2002 or at the next overhaul, whichever occurs first.\n\nThis Amendment becomes effective on 28 August 2002.","sortOrder":0}],"analysis":{"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"},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":true,"description":"Yes. Amendment 4 expands the Directive by adding additional main rotor gearbox part numbers to the mandatory inspections/replacement requirement (Background). Earlier amendments also altered inspection intervals and removed unmodified shafts from service, so the affected population and obligations have increased since the original emergency AD."},"complexity_factors":["Multiple specific part numbers affected (e.g. transmissions 28-13101-1/-1-R and 28-13101-3/-3-R) creating targeted applicability (see c and d).","Technical inspection and defect threshold: dye‑penetrant inspection and 0.005‑inch depth dividing polishable defects from mandatory replacement (see c(i)–(iii)).","Varied and short compliance timings: before further flight, within 5 hours, and recurring intervals of 25, 100 and 300 hours depending on the clause (see Compliance).","Terminating action requires installing specific replacement shaft/transmission part numbers and listed revisions (Note 1), which may have supply or installation costs.","Cross-reference to FAA AD and prior amendments creates dependency on external regulatory action and historical changes (Note 2; Background).","Operational impact choices: polish versus replace, and replacement before next overhaul or within 300 hours, impose differing downtime and cost trade-offs.","Amendment history shows successive scope and interval changes, increasing interpretive complexity for compliance tracking (Background: Amendments 1–4)."],"plain_english_summary":"This Airworthiness Directive requires owners/operators of Enstrom F‑28 helicopters fitted with specified main rotor transmission or shaft part numbers to inspect the upper shaft fillet for cracks, nicks or scratches (dye‑penetrant), polish out nicks/scratches under 0.005 inch, and replace transmissions or shafts if defects meet thresholds. It imposes short compliance times (before further flight; within 5 hours) and recurring intervals (25/100/300 hours) and allows a terminating action by installing specified large‑radius fillet parts (Note 1) (see c–d; Compliance)."},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":true,"description":"The original directive (Emergency FAA AD 76-17-08) addressed repetitive inspections of shoulder radius defects. Through four amendments, the scope has expanded significantly: Amendment 1 reduced inspection intervals; Amendment 2 mandated removal of unmodified shafts; Amendment 3 added previously unaffected helicopter models after a fatigue crack failure; and Amendment 4 (this version) expanded coverage to additional main rotor gearbox part numbers. The directive has evolved from inspection-only to mandatory replacement requirements, growing from a narrow safety inspection to a comprehensive airworthiness mandate covering multiple transmission variants."},"complexity_factors":["Multiple amendment history (Amendments 1-4) creating layered requirements that must be read together","Precise part number references with revision suffixes (-1, -1-R, -3, -3-R) and specific acceptable replacement revisions (K, L, M, N, P, R, S)","Nested conditional logic: different actions required depending on which transmission part number is installed","Multiple compliance deadlines with conditional triggers ('unless already accomplished', 'whichever occurs first')","Technical measurement threshold (0.005-inch depth) determining repair vs. replace decisions","Cross-reference to US FAA AD 2002-08-03 for additional context","Terminating action concept requires understanding of prior inspection requirements"],"plain_english_summary":"This CASA Airworthiness Directive affects Enstrom F‑28 helicopters and addresses fatigue cracking in the main rotor mast fillet that could lead to catastrophic rotor separation. It mandates dye‑penetrant inspections, polishing for very minor damage, and replacement of affected gearboxes with an improved large‑radius shaft as the terminating action, with short flight‑hour or before‑next‑flight deadlines. The AD prevents rotor failure and harmonises with the FAA directive."}},"importantCases":[],"_links":{"self":"/api/acts/ad-enst-28-9-amdt-4-main-rotor-mast","history":"/api/acts/ad-enst-28-9-amdt-4-main-rotor-mast/history","analysis":"/api/acts/ad-enst-28-9-amdt-4-main-rotor-mast/analysis","conflicts":"/api/acts/ad-enst-28-9-amdt-4-main-rotor-mast/conflicts","importantCases":"/api/acts/ad-enst-28-9-amdt-4-main-rotor-mast/important-cases","documents":"/api/acts/ad-enst-28-9-amdt-4-main-rotor-mast/documents"}}