AD/AC-SNOW/12 - Rudder Control Surface Upper Hinge - Inspection and Modification

Overview

The Civil Aviation Regulations 1998, administered by the Civil Aviation Safety Authority, include specific provisions for maintaining aircraft safety, such as the Airworthiness Directives. The particular directive AD/AC-SNOW/12 addresses issues with the rudder control surface upper hinge of Ayres Thrush (Snow) Commander Series aeroplanes, specifically models S-2D and S-2R with rudder assembly P/N 54030-87. This directive was introduced to mitigate the risk of hinge separation, which could potentially compromise flight safety. The problem it was designed to address arose from three reported instances of hinge failure on overseas aeroplanes. The objective of the directive is to ensure that inspections and necessary modifications are carried out to prevent such failures from occurring, thereby maintaining the airworthiness of the affected aircraft. The directive mandates a thorough inspection of the rudder assembly and specifies corrective actions if any cracks are detected in the upper hinge area. Compliance with these requirements must be achieved within set timeframes to ensure the continued safety and operational readiness of the aeroplanes in question. The directive was enacted to ensure that the aeroplanes meet the required safety standards and to provide clear, actionable steps for maintenance personnel to address potential issues proactively.

Scope and Application

The Civil Aviation Regulations 1998, specifically Part 39 - 105, applies to all model S-2D and S-2R Ayres Thrush (Snow) Commander Series Aeroplanes with rudder assemblies featuring a single upper hinge part number 54030-87. This regulation is concerned with ensuring the airworthiness of the specified aircraft by addressing potential structural issues with the rudder control surface upper hinge. The requirement is to inspect and, if necessary, modify the rudder assembly to prevent the possible separation of the upper hinge from the rudder assembly. The regulation applies across the Commonwealth of Australia and mandates compliance with specific inspection and modification procedures within stipulated time frames. Failure to comply with the specified requirements can result in the aircraft not being considered airworthy. The regulation is implemented under the authority of the Civil Aviation Safety Authority and is subject to amendments through subordinate instruments as necessary.

Key Provisions

The Civil Aviation Regulations 1998, specifically Part 39 - 105, contains the Civil Aviation Safety Authority Schedule of Airworthiness Directives, including AD/AC-SNOW/12 concerning the rudder control surface upper hinge for Ayres Thrush (Snow) Commander Series Aeroplanes. This directive applies to all model S-2D and S-2R aeroplanes with rudder assemblies featuring a single upper hinge part number 54030-87 (Section 1). The requirement outlined in Section 2 is to prevent the potential separation of the single upper hinge from the rudder assembly. To achieve this, the rudder assembly must be removed, the fabric and dope around the upper hinge stripped, and the area around the weld head on the upper hinge attachment inspected for cracks using 10X magnification (Section 2(a)-(c)). If cracks are discovered, one of the specified options must be followed: replacing the rudder with part number 54030-987, which has triple upper hinges, modifying the existing rudder using Ayres Custom Kit No. CK-AG-18, or replacing the defective rudder with a serviceable one of the same part number (Section 2(a)-(c)). The obligations imposed by this directive require compliance within specific timeframes. The initial inspection must occur within 100 hours of time in service after 31 July 1979 and then at intervals not exceeding 100 hours until one of the modifications outlined in Section 2(a) or (b) is completed (Section 1). The modification must be carried out no later than 300 hours of time in service after 31 July 1979 (Section 1). This ensures that the potential safety issue is addressed promptly and does not compromise the airworthiness of the aircraft. Failure to comply with the provisions of this airworthiness directive may result in serious safety risks. The potential consequences of non-compliance include the separation of the rudder assembly, which could lead to loss of control and other hazardous situations. The regulations do not explicitly state penalties for non-compliance, but non-compliance with airworthiness directives can lead to enforcement actions by the Civil Aviation Safety Authority, including the grounding of the aircraft, fines, and other legal repercussions. Ensuring adherence to these directives is crucial for maintaining the safety and airworthiness of the aircraft in operation.