AD/AC-SNOW/14 Amdt 4 - Wing Spar and Wing Attachments

Overview

The Civil Aviation Regulations 1998, under Part 39, Section 105, mandates Airworthiness Directives to ensure the safe operation of aircraft, including the Ayres Thrush (Snow) Commander Series Aeroplanes. This particular amendment, AD/AC-SNOW/14 Amendment 4, focuses on the inspection and maintenance of wing spar and wing attachment hardware. It was introduced to address the identified issues of potential structural integrity in certain aircraft models, specifically the S2D, S2R, S2R-R1820, S2R-T15, and S2R-T34, through detailed visual inspections and hardware retirement. This was enacted by the Civil Aviation Safety Authority (CASA) to mitigate risks associated with structural fatigue and fuel leakage, ensuring compliance with safety standards. The objective is to maintain the airworthiness of these aircraft by adhering to the specified inspection intervals and hardware retirement timelines, thereby enhancing overall aviation safety.

Scope and Application

The Civil Aviation Regulations 1998, under Part 39 - 105, mandates specific airworthiness directives for the maintenance and inspection of Ayres Thrush (Snow) Commander Series Aeroplanes. This regulation applies to all models S2D, S2R, S2R-R1820, S2R-T15, and S2R-T34, ensuring compliance with specified safety standards. The directives focus on critical areas such as the lower wing spar centre section, wing main spar, and wing attachment hardware, requiring visual inspections and specific maintenance actions to ensure airworthiness. Compliance with these directives is mandatory for all relevant aircraft within the specified timeframes and intervals, with additional considerations for aircraft equipped with certain wing tip extensions. The directive is effective as of 14 September 1995, and the inspection and maintenance requirements are designed based on fatigue and fail-safe analyses conducted by the manufacturer.

Key Provisions

The Civil Aviation Regulations 1998, particularly Part 39 - 105, contain specific Airworthiness Directives (AD) for certain aircraft models. For the Ayres Thrush (Snow) Commander Series Aeroplanes, AD/AC-SNOW/14 Amendment 4 outlines requirements concerning the wing spar and attachments. Section 1 mandates a visual inspection of the lower wing spar centre section in accordance with Ayres Corporation Service Letter SL-AG-97. Section 2 requires a more detailed inspection of the wing main spar and attachment hardware for specific aircraft models, as per Ayres Corporation Service Bulletin SB-AG-23. This inspection also involves checking the lower surface of the wing for fuel leakage, and if detected, inspecting the forward face of the wing main spar web for cracks. Section 3 directs the retirement of the wing main spar lower cap assembly from service. Compliance with these requirements is critical, with specific timelines and intervals provided for initial and recurring inspections, and retirement. The obligations imposed by these regulations are stringent and time-bound. Operators of the affected aircraft models must ensure that the specified inspections are conducted within the stipulated timeframes. For instance, the initial inspection of the lower wing spar centre section must occur before 2500 hours' time in service or before 100 hours' time in service after 14 September 1995, whichever is later. For other inspections, the initial check must be completed before 250 hours' time in service after 14 September 1995 or before 14 September 1996, whichever is earlier. Recurring inspections must then be performed at intervals not exceeding 500 hours' time in service. Additionally, the wing main spar lower cap assembly must be retired before 25000 hours' time in service. Aircraft equipped with FAA STC SA 1463 NM (46.5 inch wing tip extensions) must adhere to halved threshold and interval values unless the Civil Aviation Safety Authority lifts the limitation based on fatigue and fail-safe substantiation data. Failure to comply with these ADs can lead to severe consequences. The regulations do not explicitly state the penalties for non-compliance; however, non-compliance with airworthiness directives is a serious matter under Australian aviation law. Potential consequences may include enforcement actions by the Civil Aviation Safety Authority, such as fines, suspension, or revocation of the aircraft's certificate of airworthiness. Such actions could result in the grounding of the aircraft, leading to significant operational disruptions and financial losses for the operator. Additionally, non-compliance could potentially result in criminal charges if it is deemed that the failure to adhere to the ADs contributed to an aviation accident or incident.