{"id":"F2006B11386","name":"AD/MU-2/56 - Underspeed Governor Minimum Stop","slug":"ad-mu-2-56-underspeed-governor-minimum-stop","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":57287,"registerId":"commonwealth-F2006B11386-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/MU-2/56 - Underspeed Governor Minimum Stop","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)  \nMitsubishi MU-2 Series Aeroplanes\n\nAD/MU-2/56 Underspeed Governor Minimum Stop 9/94 DM\n\nApplicability: All MU-2B-26A, \\-36A, \\-40 and \\-60 aircraft and any MU-2B-36 aircraft previously modified in accordance with FAA Supplemental Type Certificate SA2413SW.\n\nRequirement: 1. Action in accordance with the technical requirements of paragraphs (a) (b) (c) (d) & (e) of FAA AD 94-11-04 Amdt 39-8920.\n\n2. Amend the Limitations Section of the Aircraft Flight Manual (AFM) to include the minimum engine idle speed of 76.5%.\n\nNote: The applicable Green Page amendment to the AFM will be available from Civil Aviation Authority District Offices.\n\nCompliance: Unless previously carried out within 25 hours time in service from 29 June 1994.\n\nNote: CAO 107 AD/PHZL/64 mandates inspection of the propeller hub arms.\n\nBackground: During investigation following a fatal accident it was discovered that a reduction in the fatigue strength of the propeller hub could occur because of high vibration frequencies during ground idle speed.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":true,"description":"This directive imposes a new operational limitation (minimum engine idle speed 76.5%) and mandates actions from FAA AD 94-11-04 on the listed MU-2 variants (Requirement 1 & 2; Applicability). It broadens mandatory maintenance/operational requirements for affected aircraft and creates an immediate compliance obligation (Compliance)."},"complexity_factors":["Cross-reference to FAA AD 94-11-04 (Requirement 1) — operator must obtain and follow another instrument's technical paragraphs (a)-(e), adding procedural and interpretive steps.","Mandatory AFM amendment to set minimum idle speed 76.5% (Requirement 2) — requires flight manual revision, distribution and record‑keeping by operators.","Tight short compliance window (25 hours TIS from 29 June 1994) (Compliance) — creates operational scheduling pressure for affected aircraft.","Narrow model applicability but includes FAA STC-modified aircraft (Applicability) — need to check modification status of individual airframes, increasing administrative verification.","Related mandatory inspection referenced separately (CAO 107 AD/PHZL/64) (Note) — operators must coordinate multiple directives and inspections.","Administrative support: Green Page AFM amendment availability via CASA District Offices (Note) — introduces dependency on regulator for official AFM text."],"plain_english_summary":"Requires owners/operators of specified Mitsubishi MU-2B-26A, -36A, -40 and -60 aeroplanes (and MU-2B-36s modified under FAA STC SA2413SW) to carry out the corrective actions set out in FAA AD 94‑11‑04 and to add a minimum engine idle speed of 76.5% to the Aircraft Flight Manual. Compliance is required within 25 hours time in service from 29 June 1994. The directive responds to propeller‑hub fatigue risk from high vibration at ground idle."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific technical failure mode identified through accident investigation. It has not expanded beyond its original purpose of preventing propeller hub fatigue through minimum idle speed requirements."},"complexity_factors":["Single specific aircraft type and limited model variants (5 specific models)","Requires cross-reference to external US FAA technical document (FAA AD 94-11-04) for actual implementation details","Contains one substantive technical requirement plus administrative action (flight manual amendment)","Short document (approximately 200 words) with clear structure","Single compliance condition with straightforward time-in-service calculation","No nested definitions or conditional exceptions within the directive itself"],"plain_english_summary":"This mandatory CASA Airworthiness Directive requires certain Mitsubishi MU-2 models to have their underspeed governor modified and the Aircraft Flight Manual updated to prohibit engine idle below 76.5% Np. It affects MU-2B-26A, -36A, -40, -60 and some MU-2B-36s modified under FAA STC SA2413SW.\n\nThe action responds to a fatal accident where low ground idle caused high‑frequency vibration and propeller‑hub fatigue that can lead to failure; compliance was required within 25 flight hours after 29 June 1994."}},"importantCases":[],"_links":{"self":"/api/acts/ad-mu-2-56-underspeed-governor-minimum-stop","history":"/api/acts/ad-mu-2-56-underspeed-governor-minimum-stop/history","analysis":"/api/acts/ad-mu-2-56-underspeed-governor-minimum-stop/analysis","conflicts":"/api/acts/ad-mu-2-56-underspeed-governor-minimum-stop/conflicts","importantCases":"/api/acts/ad-mu-2-56-underspeed-governor-minimum-stop/important-cases","documents":"/api/acts/ad-mu-2-56-underspeed-governor-minimum-stop/documents"}}