Overview

The Airworthiness Directive AD/T53/21, issued in 2002 by the Civil Aviation Safety Authority (CASA) delegate, addresses the problem of vibrations within the reduction gearbox of AlliedSignal (Lycoming) Turbine Engines - T53 Series, which can cause failure of the tachometer drive spur gear. This failure has the potential to result in overspeed of the engine and loss of power turbine speed indication. The directive was enacted to ensure the safety of these aircraft by requiring special vibration tests to detect potential issues and mandate timely replacement of the reduction gearbox or the entire engine, as necessary. This legislative instrument aims to maintain the airworthiness of the specified engines by implementing stringent testing and replacement protocols to prevent unsafe conditions arising from gearbox failures.

Scope and Application

The Airworthiness Directive (AD) issued under the Civil Aviation Regulations 1998 applies specifically to certain models of AlliedSignal (Lycoming) T53 Series turbine engines, including T5311A, T5311B, T5313B, T5317A, T5317B, T53-L-11, T53-L-11A, T53-L-11B, T53-L-11C, T53-L-11D, T53-L-11A S/SA, T53-L-13B, T53-L-13B S/SA, T53-L-13B S/SB and T53-L-703. This directive mandates that specific actions be taken to address an unsafe condition identified in the tachometer drive spur gear of these engines. The directive requires initial and repetitive special vibration tests as well as replacement of the reduction gearbox assembly or the entire engine if the tests indicate a failure. The directive is issued by the delegate of the Civil Aviation Safety Authority (CASA) and is effective from 5 September 2002, with specific compliance timelines for the tests and replacements. The directive is applicable across the Commonwealth of Australia, and its requirements are detailed in the AD, which was also published in the Commonwealth of Australia Gazette on 14 August 2002.

Key Provisions

The Airworthiness Directive (AD) AD/T53/21 issued under subregulation 39.1(1) of the Civil Aviation Regulations 1998 mandates specific actions to address the safety concerns associated with certain AlliedSignal (Lycoming) Turbine Engines. The AD applies to engines such as the T5311A, T5311B, T5313B, T5317A, T5317B, T53-L-11, T53-L-11A, T53-L-11B, T53-L-11C, T53-L-11D, T53-L-11A S/SA, T53-L-13B, T53-L-13B S/SA, T53-L-13B S/SB, and T53-L-703. The directive requires the performance of special vibration tests as outlined in Table 1 of the requirement section, which specifies the service bulletins to be followed for different engine models. If an engine fails the special vibration test, it mandates either the replacement of the reduction gearbox assembly or the entire engine, followed by another special vibration test. Operators of the affected engines must comply with the AD by conducting initial and repetitive special vibration tests at specified intervals. The initial inspection must be completed within 100 hours of aircraft time in service from the effective date of the directive, which is 5 September 2002. For engines with tachometer drive spur gear part number 1-070-062-04, the repetitive test must occur at 500 flight hour intervals since the last test. For those with part number 1-070-062-06, the repetitive test must occur at 1000 flight hour intervals. Replacement of the engine or gearbox must be completed before further flight if the engine fails the test. Failure to comply with the AD may result in serious safety risks, including potential engine overspeed and loss of power turbine speed indication. The directive is a legal requirement, and non-compliance could have severe consequences for airworthiness and safety. The Civil Aviation Safety Authority (CASA) enforces these regulations, and any breaches may lead to enforcement actions, penalties, or other legal consequences as prescribed by relevant laws and regulations.