AD/AL 250/41 Amdt 5 - Third Stage Turbine Wheel - Inspection and RPM Operational Restrictions

Overview

The Civil Aviation Regulations 1998, under Part 39, include specific Airworthiness Directives designed to ensure the safety and reliability of aircraft operations in Australia. One such directive, AD/AL 250/41 Amendment 5, addresses issues related to the Allison Turbine Engines - 250 Series by imposing inspection requirements and operational restrictions on the third stage turbine wheel. This directive was introduced to address safety concerns identified in certain models of the 250 Series engines that were not fitted with solid blade shroud third stage turbine wheels. The objective of this directive, enacted by the Civil Aviation Safety Authority, is to mitigate potential risks associated with these engines through mandatory inspections and operational limitations. Compliance with this directive is enforced through reference to specific manufacturer documents, ensuring that all affected aircraft meet the necessary safety standards. The enactment of this directive by the Commonwealth of Australia’s Civil Aviation Safety Authority underscores the commitment to maintaining high safety standards in the aviation industry. By specifying the need for particular placards and operational restrictions, the directive aims to prevent accidents and ensure the continued airworthiness of affected aircraft. The directive applies to specific models of the Allison Turbine Engines and mandates the replacement of non-solid blade shroud wheels to avoid operational speed restrictions. This proactive approach ensures that any potential hazards are identified and addressed, thereby enhancing overall aviation safety.

Scope and Application

The Civil Aviation Regulations 1998, specifically Part 39 - 106, applies to the Allison Turbine Engines - 250 Series, with a focus on the inspection and operational restrictions for the third stage turbine wheel. This directive is pertinent to all models 250-C20, C20B, C20F, B17, B17B, B17C, and B17D that are not fitted with solid blade shroud third stage turbine wheels. The regulation mandates the installation of specific placards to inform pilots of operational speed restrictions, particularly during ground operations and under certain environmental conditions. The geographic reach of these regulations is national, applying throughout the Commonwealth of Australia. Subordinate instruments may further detail specific compliance requirements and enforcement mechanisms. The regulation does not explicitly state exclusions or thresholds but implies that compliance is mandatory for the specified engine models until all affected turbine wheels are replaced. The directive extends its application by referencing relevant FAA advisories and manufacturer's documents, ensuring alignment with international safety standards.

Key Provisions

The Civil Aviation Regulations 1998, specifically Part 39 - 106, sets forth Airworthiness Directives (AD) that govern the maintenance and operation of certain aircraft components. In this instance, AD/AL 250/41 Amendment 5 focuses on the Allison Turbine Engines - 250 Series, specifically the third stage turbine wheel. The directive applies to all models 250-C20, C20B, C20F, B17, B17B, B17C, and B17D not equipped with solid blade shroud third stage turbine wheels (section 1). The directive references Allison 250-C20, C20B, C20F, CEB-A-1174 Rev. 3 and Allison 250-B17, B17B, B17C, B17D, CEB-A-1146 Rev. 3 as the applicable documents, and notes that FAA AD 83-03-02 R1 is also relevant. The AD mandates that until all affected turbine wheels are replaced with solid blade shroud wheels, a placard must be installed on or adjacent to the aircraft’s installed N2 tacho indicator, prohibiting sustained operation between 90 and 98% N2. For C20, C20B, and C20F powered aircraft, a placard must also be installed clearly visible to the pilot stating that during all ground operations, the engine N1 speed must be maintained at ground idle, except during transient operation, when performing required operational checks, in high or gusty wind conditions, or where safety would be adversely affected (section 3). For B17, B17B, B17C, and B17D powered aircraft, a similar placard must state that during all ground operations, the engine N2 speed must be maintained below 90% N2 RPM, except under the same exceptions (section 4). Compliance with these directives is to be achieved in accordance with the referenced documents. Entities governed by this AD must adhere to several obligations and requirements. Primarily, they must inspect the third stage turbine wheels of the specified engine models and replace any non-solid blade shroud wheels as mandated. They must also install the required placards clearly visible to the pilots, ensuring that all operational instructions are followed meticulously. The directive further requires adherence to the phased replacement schedule for the turbine wheels, prohibiting the re-installation of any superseded wheels. Non-compliance with these directives can lead to serious safety issues and may result in the aircraft being deemed unairworthy. Failure to comply with the AD/AL 250/41 Amendment 5 can lead to significant legal and safety consequences. Civil penalties may be imposed for non-compliance, and the aircraft may be grounded until the necessary modifications and inspections are completed. In severe cases, criminal penalties could apply, especially if non-compliance results in an accident or significant safety risk. The maximum penalties for such violations are determined by the Civil Aviation Safety Authority and can include substantial fines and potential imprisonment for individuals found in breach of the regulations.