AD/AC-SNOW/17 - Outer Wing Huck Bolts

Overview

The Civil Aviation Regulations 1998, enacted by the Parliament of Australia, serve as the primary regulatory framework for civil aviation within the country, addressing various safety and operational aspects. Part 39, specifically, includes a series of airworthiness directives aimed at ensuring that aircraft meet necessary safety standards. One such directive, AD/AC-SNOW/17, pertains to the Ayres Thrush (Snow) Commander Series Aeroplanes and focuses on the replacement of outer wing Huck bolts. This directive was introduced to address a significant safety concern identified by a local operator, which reported instances of sheared Huck bolts and structural damage to the wing spars. The policy objective of this directive is to prevent catastrophic failure by mandating repetitive inspections and timely replacement of the identified faulty components, ensuring the continued airworthiness of the affected aircraft models. The directive requires compliance with specific timelines and procedures, as outlined in Ayres Corporation Service Bulletin SB-AG-33, ensuring that the necessary actions are taken within defined intervals of flight hours. The directive aims to mitigate the risk of progressive fastener failure by enforcing the replacement of existing aluminium Huck bolts with more durable steel Huck bolts or NAS bolts. This legislative instrument underscores the importance of continuous monitoring and maintenance to uphold the safety standards required by Australian civil aviation regulations.

Scope and Application

The Civil Aviation Regulations 1998, under Part 39 - 105, specifically mandate the application of the Civil Aviation Safety Authority (CASA) Schedule of Airworthiness Directives for Ayres Thrush (Snow) Commander Series Aeroplanes, with a focus on the outer wing Huck bolts as detailed in AD/AC-SNOW/17. This legislation applies to specific models and serial numbers of the Ayres Thrush (Snow) Commander Series Aeroplanes, and its scope is to ensure the airworthiness of these aircraft by mandating compliance with the Service Bulletin SB-AG-33 from the Ayres Corporation. The directive applies nationally within the Commonwealth of Australia and is enforceable by CASA. The legislation specifies that compliance must be achieved through two parts: Part I requires inspections to be conducted within 10 hours of service after 18 March 1993, and then at intervals not exceeding 100 hours of service until Part II is fulfilled. Part II demands inspections to be carried out within 500 hours of service following the same date. This regulatory framework is intended to mitigate the risk of catastrophic failure due to progressive fastener failure in the outer wing sections.

Key Provisions

The Civil Aviation Regulations 1998, specifically Part 39 - 105, mandates the implementation of the Civil Aviation Safety Authority's Airworthiness Directive (AD) concerning the Ayres Thrush (Snow) Commander Series Aeroplanes, particularly focusing on the outer wing Huck bolts (AD/AC-SNOW/17). This directive applies to specific models and serial numbers outlined in the Requirement Document (section 1). The core requirement is compliance with Ayres Corporation Service Bulletin SB-AG-33, including Accomplishment Instructions Parts I and II (section 2). In terms of compliance, for Part I, operators must conduct inspections within 10 hours of service following 18 March 1993 and subsequently at intervals not exceeding 100 hours of service until Part II is fulfilled (section 3). For Part II, inspections must occur within 500 hours of service after the same date (section 4). These provisions aim to address the critical safety concern identified in a recent report of sheared Huck bolts on the outer section of both wing upper spar caps, with the left-hand spar web also found creased at WS 183 upper (section 5). The manufacturer has deemed progressive fastener failure from the wing tip towards the root as catastrophic, necessitating continuous inspections to prevent such failures by replacing existing aluminium Huck bolts with steel Huck bolts or NAS bolts (section 6). The Act imposes several obligations on the operators of the specified Ayres Thrush aircraft. Primarily, operators must adhere to the inspection and replacement schedule outlined in the directive (section 7). They must ensure that inspections are conducted as required and that any identified issues are promptly addressed in accordance with the instructions provided by Ayres Corporation (section 8). Moreover, operators must maintain records of all inspections and actions taken to comply with the directive, as this documentation may be required for audits or inspections by the Civil Aviation Safety Authority (section 9). Failure to comply with these obligations can result in significant safety risks, potentially leading to catastrophic failures in flight. Failure to comply with the requirements of the Airworthiness Directive may result in civil and criminal consequences. Under the Civil Aviation Act 1988, non-compliance can lead to enforcement actions by the Civil Aviation Safety Authority, including fines and other administrative penalties (section 10). Additionally, the severity of the non-compliance could result in the grounding of the aircraft until the necessary actions are taken to meet the directive's requirements (section 11). In cases where the non-compliance leads to an accident or incident, the operator could face criminal charges, including potential imprisonment, as the directive is designed to prevent catastrophic failures that could endanger lives (section 12). The maximum penalties for such offences can vary, but they are intended to enforce strict adherence to the safety directives issued by the Civil Aviation Safety Authority (section 13).