AD/TPE 331/45 - Third Stage Stator Assembly

Overview

The Civil Aviation Regulations 1998, enacted by the Parliament of the Commonwealth of Australia, form a comprehensive body of rules that govern the operation and maintenance of aircraft within Australian airspace. This particular legislation, specifically within Part 39, addresses the airworthiness of aircraft components and is instrumental in ensuring that aircraft meet the necessary safety standards. The Civil Aviation Regulations were introduced to fill the need for a robust regulatory framework that maintains high safety standards in civil aviation, thereby protecting the public and promoting the safe, efficient, and orderly development of air navigation facilities. The policy objective of these regulations is to safeguard lives and property by ensuring that all aspects of civil aviation operations are conducted in a manner that minimises risk.

Scope and Application

The Civil Aviation Regulations 1998, specifically Part 39 - 106, issued by the Civil Aviation Safety Authority, governs the airworthiness directives for certain AlliedSignal (Garrett/AiResearch) turbine engines. This legislation applies to the TPE 331 series engines, particularly those with third stage stator assemblies repaired at National Flight Services (USA) between 20 February 1990 and 6 April 1992, and identified by serial numbers listed in National Flight Services Alert Bulletin NF331-A72-11921 dated 9 November 1992. The directive mandates the replacement of these specific third stage stator assemblies to mitigate the risk of uncontained engine failure due to material fatigue. Compliance with this airworthiness directive is mandatory for operators of affected aircraft, requiring replacements within specified cycles post 24 December 1992, depending on the engine's cycle count at the time of the directive's issuance. The regulation extends to all aircraft within the Commonwealth of Australia, ensuring adherence to national safety standards.

Key Provisions

The Civil Aviation Regulations 1998, specifically Part 39 - 106, include an Airworthiness Directive (AD) pertaining to the AlliedSignal (Garrett/AiResearch) Turbine Engines - TPE 331 Series. This AD, numbered AD/TPE 331/45, mandates the replacement of certain third stage stator assemblies. According to section (2/93), the directive applies to TPE 331-1,-2,-2UA,-3U,-3UW,-5,5A,-6 and 6A Turboprop and TSE331-3U Turboshaft engines that have third stage stator assemblies part number 868379-3 repaired at National Flight Services (USA) between 20 February 1990 and 6 April 1992. These assemblies must be identified by the serial numbers listed in the National Flight Services Alert Bulletin NF331-A72-11921 dated 9 November 1992. Under section (a), the requirement is to replace the identified third stage stator assemblies with serviceable assemblies. Compliance with this directive involves a specific schedule based on the number of cycles the assemblies have accumulated since the repair by National Flight Services. For assemblies with 900 or more cycles, the replacement must occur within 50 cycles from 24 December 1992. For those with 450 to 899 cycles, the replacement must happen within 150 cycles in service from 24 December 1992, but not to exceed 950 cycles. Assemblies with less than 450 cycles must be replaced before they accumulate 600 cycles. In cases where the number of cycles cannot be determined, it is calculated by multiplying the third stage stator assembly hours in service by 1.5. The AD also notes that the Federal Aviation Administration (FAA) has issued Priority Letter AD 92-26-08, which refers to this directive. The background information provided by the FAA indicates that a Hastelloy S material inner seal support in the third stage stator assembly may fatigue crack, move aft, and make contact with the third stage turbine wheel, potentially leading to an uncontained engine failure. Reports indicate that some of these assemblies were repaired using Hastelloy S material instead of the approved Haynes 25 material, leading to a significantly reduced fatigue life. The FAA has determined that Hastelloy S has approximately one-sixth of the expected fatigue life in this application, and if not removed from service, it can result in uncontained failure of the third stage turbine wheel. Failure to comply with these AD requirements could result in severe operational risks, including engine failure and potential accidents. Under the Civil Aviation Act 1988, non-compliance with airworthiness directives can lead to civil penalties, including fines and potential prosecution. In the event of an accident caused by non-compliance, the operator or individual responsible could face criminal charges, leading to imprisonment. The specific penalties are not detailed in the AD but are governed by the broader legislative framework within which these regulations operate.