AD/AL 250/61 Amdt 3 - Gas Producer Turbine Assembly and Second Stage Nozzle Seal

Overview

The Civil Aviation Regulations 1998, under the authority of the Civil Aviation Safety Authority (CASA), was enacted to ensure the safety of civil aviation operations in Australia. Among the various regulations, Part 39 specifically addresses airworthiness directives, which are crucial in maintaining the safety standards of aircraft engines and components. The specific legislative instrument F2006B02272 pertains to Allison Turbine Engines - 250 Series, targeting issues related to the gas producer turbine assembly and the second stage nozzle seal. This directive was introduced to address potential safety risks associated with these components, ensuring they meet the necessary safety and operational standards. The policy objective of these regulations is to mitigate risks and maintain the highest safety standards for all civil aviation activities within Australia. The legislation mandates specific inspection and compliance procedures for certain Allison 250-C30/C30S engines used in Sikorsky S-76 aircraft. It requires inspections for evidence of rubbing on the second stage turbine 29-34 labyrinth seal and adjustments to the seal clearance, ensuring these engines operate safely and efficiently. Compliance with these directives is essential to avoid potential mechanical failures and ensure the continued airworthiness of affected aircraft. The regulations also outline the timeline for inspections and adjustments, providing clear guidelines for maintenance personnel to follow in order to meet these safety requirements.

Scope and Application

The Civil Aviation Regulations 1998, specifically Part 39 - 106, pertains to the Civil Aviation Safety Authority’s Schedule of Airworthiness Directives, which includes the Allison Turbine Engines - 250 Series AD/AL 250/61 Amendment 3. This regulation applies to all 250-C30/C30S engines installed in or intended for installation in Sikorsky S-76 aircraft, as well as all C30 series engines with specific serial numbers detailed in the Requirement Document. The scope of this legislation is thus targeted at particular engine models and their installations in specific aircraft types. This directive is applicable on a national level within Australia, governed by the Commonwealth of Australia. The regulation requires two primary actions: inspecting the second stage turbine 29-34 labyrinth seal for rub, and increasing the second stage nozzle 29-34 labyrinth seal clearance. Compliance requirements are stringent, with specific timelines and conditions, such as engines having 100 hours or less time in service since a turbine rotor assembly overhaul, repair, or disassembly. The requirement for inspections and modifications must be adhered to within specified periods post the amendment's issuance date. The regulation also acknowledges compliance with previous versions of the directive as meeting the requirements of this amendment.

Key Provisions

The Civil Aviation Regulations 1998, under Part 39, particularly Section 106, establish the Civil Aviation Safety Authority (CASA) Schedule of Airworthiness Directives, specifically targeting Allison Turbine Engines 250 Series. This directive, AD/AL 250/61 Amendment 3, mandates critical maintenance actions for the gas producer turbine assembly and second stage nozzle seal of certain turbine engines (Section 1). It applies to all 250-C30/C30S engines installed in or intended for installation in Sikorsky S-76 aircraft and all C30 series engines with specific serial numbers (Section 2). The directive requires two primary actions: inspecting the second stage turbine 29-34 labyrinth seal for any rub damage as outlined in Allison CEB-A-72-3127R.3, and increasing the clearance of the second stage nozzle 29-34 labyrinth seal according to Allison CEB-A-72-3131, Revision 1 (Section 3). Compliance with these requirements is structured around the operational hours of the engines. For engines with 100 hours or less since their last overhaul, repair, or disassembly, the inspection of the second stage turbine nozzle interstage seal must occur within the next 50 hours after 5 September 1984 (Section 4). Moreover, the seal clearance adjustments should be made concurrently with the inspection if the engines were assembled following CEB-A-72-3127 Revision 1. For engines assembled according to CEB-A-72-3127 or Allison Message THO-1977W-RMG-84, these adjustments must be completed no later than the next certified overhaul following 28 February 1985 (Section 4). Compliance with the previous version of this directive is considered equivalent to compliance with the current amendment. The obligations imposed by this directive are clear and specific, ensuring the safety and operational integrity of the targeted turbine engines. Aircraft operators and maintenance personnel must adhere to the outlined inspection and maintenance procedures to ensure compliance with the regulations. Failure to comply with these requirements can result in serious safety issues, potentially leading to engine failure or other critical malfunctions during flight. Consequently, the directive underscores the importance of timely and precise maintenance actions to prevent any operational hazards.