AD/MU-2/56 - Underspeed Governor Minimum Stop

Overview

The Civil Aviation Regulations 1998, particularly Part 39 - 105, encompasses the Civil Aviation Safety Authority’s schedule of airworthiness directives, addressing specific safety concerns associated with certain aircraft types. One such directive, AD/MU-2/56, focuses on Mitsubishi MU-2 series aeroplanes, specifically addressing the issue of underspeed governor minimum stop. This directive was enacted to ensure that all MU-2B-26A, -36A, -40, and -60 aircraft, as well as any MU-2B-36 aircraft previously modified under FAA Supplemental Type Certificate SA2413SW, adhere to stringent safety requirements to prevent a reduction in the fatigue strength of the propeller hub, which could occur due to high vibration frequencies during ground idle speed. The directive was introduced following an investigation into a fatal accident, highlighting the importance of timely compliance to mitigate such risks. The objective of this legislation, as enacted by the Commonwealth of Australia, is to mandate specific actions and amendments to aircraft manuals to ensure operational safety. The Civil Aviation Safety Authority, under the authority of the Civil Aviation Act 1988, ensures that these directives are enforced to maintain high safety standards within the aviation industry. Compliance with these directives is critical, as failure to adhere to the specified timelines and technical requirements can lead to significant safety hazards.

Scope and Application

The Civil Aviation Regulations 1998, specifically Part 39 - 105 and the Civil Aviation Safety Authority Schedule of Airworthiness Directives, apply to Mitsubishi MU-2 Series aeroplanes, including MU-2B-26A, -36A, -40, and -60 aircraft as well as MU-2B-36 aircraft that have been previously modified in accordance with FAA Supplemental Type Certificate SA2413SW. This legislation mandates adherence to the technical requirements detailed in FAA AD 94-11-04 Amendment 39-8920, which encompasses several specified actions. Additionally, operators are required to amend the Limitations Section of the Aircraft Flight Manual (AFM) to include the minimum engine idle speed of 76.5%, with the updated Green Page amendment available from Civil Aviation Authority District Offices. Compliance with these directives is necessary unless the required actions have already been executed within 25 hours of time in service from 29 June 1994. Furthermore, CAO 107 AD/PHZL/64 mandates inspection of the propeller hub arms. These regulations were enacted following an investigation into a fatal accident, which revealed that high vibration frequencies during ground idle speed could lead to a reduction in the fatigue strength of the propeller hub.

Key Provisions

The Civil Aviation Regulations 1998, particularly under Part 39 - 105, include specific directives aimed at ensuring the safety and airworthiness of certain aircraft. In this context, AD/MU-2/56 pertains to Mitsubishi MU-2 series aeroplanes and mandates compliance with the technical requirements outlined in FAA AD 94-11-04 Amdt 39-8920 (section 1). Specifically, the directive requires operators to implement actions corresponding to paragraphs (a) to (e) of the mentioned amendment, which likely involve specific maintenance or modification procedures for the underspeed governor and other related components to prevent a reduction in the fatigue strength of the propeller hub due to high vibration frequencies during ground idle speed. Additionally, section 2 of AD/MU-2/56 requires operators to amend the Limitations Section of the Aircraft Flight Manual (AFM) to reflect the minimum engine idle speed of 76.5%. Operators of the affected MU-2B-26A, -36A, -40, and -60 aircraft, as well as any MU-2B-36 aircraft previously modified in accordance with FAA Supplemental Type Certificate SA2413SW, are subject to these requirements. The compliance timeline stipulates that these actions must be carried out unless they have already been completed within 25 hours of time in service from 29 June 1994. The directive also references CAO 107 AD/PHZL/64, which mandates an inspection of the propeller hub arms. This underscores the comprehensive approach taken by the Civil Aviation Safety Authority to mitigate safety risks associated with the identified issue. Failure to comply with the provisions of AD/MU-2/56 could result in significant consequences. Operators who do not adhere to the mandated actions and amendments may face regulatory penalties. The exact nature of these penalties is not explicitly stated in the directive, but it is likely that non-compliance could lead to enforcement actions by the Civil Aviation Safety Authority, which may include fines, mandatory corrective actions, or even grounding of the aircraft until compliance is achieved. The regulatory oversight ensures that all operators maintain the highest standards of safety and airworthiness for their Mitsubishi MU-2 series aeroplanes.