AD/T53/19 - N2 Accessory Drive

Overview

The Civil Aviation Regulations 1998, as amended by the legislative instrument F2006B07248, address critical safety concerns related to the operation of AlliedSignal (formerly Textron Lycoming) T53 Series turbine engines. Enacted by the Commonwealth of Australia, this legislation aims to mitigate the risk of uncommanded engine acceleration due to the disengagement of the N2 accessory drive assembly, which can occur if the N2 spur gear nut retainers separate from the engine. This problem was identified through reports of retainer separations, which could lead to potentially hazardous situations during aircraft operation. The policy objective of the regulation is to ensure the safety of civil aviation by enforcing compliance with specific maintenance requirements for these engines, as detailed in the AlliedSignal Aerospace Service Bulletins. This airworthiness directive became effective on 17 July 1997, mandating compliance within 300 hours of service or before 17 July 1999, whichever comes first.

Scope and Application

The Civil Aviation Regulations 1998, specifically Part 39 – 106 Civil Aviation Safety Authority Schedule of Airworthiness Directives, pertains to the AlliedSignal (Lycoming) Turbine Engines - T53 Series and mandates the removal of N2 spur gear nut retainers to mitigate the risk of uncommanded engine acceleration. This directive applies to engines such as the T5311, T5313, T5317, T53-L-11, T53-L-13, and T53-L-703 series manufactured by AlliedSignal (formerly Textron Lycoming). The requirement is to prevent possible uncommanded engine acceleration that may result from the disengagement of the N2 accessory drive assembly due to the separation of the N2 spur gear nut retainers, specifically part number 1-070-066-01. Compliance with this directive must be achieved within 300 hours of time in service or before 17 July 1999, whichever comes first, and it became effective on 17 July 1997. The directive references FAA Airworthiness Directive 97-07-05 and specifies different AlliedSignal Aerospace Service Bulletins for different engine types to guide the compliance process.

Key Provisions

The main operative sections of this airworthiness directive (AD/T53/19) pertain to the removal of specific parts from certain AlliedSignal (Lycoming) T53 series turbine engines to prevent uncommanded engine acceleration. Section 1 details the applicability of the directive, specifying that it applies to AlliedSignal T5311, T5313, T5317, T53-L-11, T53-L-13, and T53-L-703 series engines. Section 2 outlines the requirement, which involves the removal of N2 spur gear nut retainers (lock cups) part number 1-070-066-01 to prevent potential disengagement of the N2 accessory drive assembly and subsequent uncommanded engine acceleration. Compliance must be achieved within 300 hours of time in service or before 17 July 1999, whichever comes first. The directive became effective on 17 July 1997. The obligations imposed by this directive on the parties and entities it governs include the necessity to remove the specified N2 spur gear nut retainers from the applicable engines. Operators and owners of these engines must ensure that the directive is complied with within the specified timeframes. The directive references specific AlliedSignal Aerospace Service Bulletins (SB) that detail the procedures for the removal of the parts. These bulletins provide the necessary guidance and instructions to properly conduct the removal and ensure the safety of the engines. The consequences of non-compliance with this airworthiness directive can include significant safety risks, such as uncommanded engine acceleration, which could lead to severe incidents. Although the Civil Aviation Regulations 1998 do not explicitly state maximum penalties for non-compliance with this directive, failure to adhere to airworthiness directives can result in serious civil or criminal consequences. These may include fines, suspension or revocation of airworthiness certificates, and potential criminal charges if the non-compliance leads to accidents or incidents. The Civil Aviation Safety Authority (CASA) has the authority to enforce compliance and take appropriate action against entities that fail to adhere to airworthiness directives.