Overview

The Civil Aviation Safety Authority (CASA) introduced the Airworthiness Directive (AD) AD/APU/16 under subregulation 39.1(1) of the Civil Aviation Regulations 1998 (CAR 1998) to address the problem of uncontained compressor wheel failures in specific models of Hamilton Standard Power Systems Auxiliary Power Units (APU). This AD, which became effective on 31 October 2002, mandates the replacement of cast steel and wrought steel compressor wheels in the T-62T-2C, T-62T-25, T-62T-29, and T-62T-39 APU models with part numbers 100636-1, to prevent potential failures that could lead to damage to the aircraft. The directive was issued to ensure the continued safety of these aircraft by imposing specific cycle limits and replacement timelines for the affected compressor wheels, as identified by their serial numbers and casting lot vendor identification numbers.

Scope and Application

The Airworthiness Directive (AD) issued by the Civil Aviation Safety Authority (CASA) applies specifically to Hamilton Standard Power Systems (formerly Sundstrand Power Systems, Turbomach, and Solar) models T-62T-2C, T-62T-25, T-62T-29, and T-62T-39 Auxiliary Power Units (APU) that have compressor wheel part number 100636-1 installed. This directive mandates that the specified compressor wheels be replaced under certain conditions to ensure the airworthiness and safety of the aircraft. The AD specifies that cast steel compressor wheels identifiable by a four digit casting lot vendor identification number used as a prefix to the serial number, must be replaced with P/N 4503164, 4504174, or M4504174. Similarly, wrought steel compressor wheels identifiable by a serial number beginning with the letter “W” must also be replaced with the same part numbers. The replacement is required at specific cycle limits and within certain timeframes after the effective date of the directive. This AD is applicable within the Commonwealth of Australia and was published in the Commonwealth of Australia Gazette on 9 October 2002, becoming effective on 31 October 2002.

Key Provisions

The main operative sections of this Airworthiness Directive (AD) concern the replacement of specific compressor wheels in certain models of Hamilton Standard Power Systems (formerly Sundstrand Power Systems, Turbomach, and Solar) auxiliary power units (APU). Section (a) of the applicability section specifies the models and parts affected, namely the T-62T-2C, T-62T-25, T-62T-29, and T-62T-39 APUs with a cast steel compressor wheel part number (P/N) 100636-1 installed. Similarly, section (b) applies to APUs with a wrought steel compressor wheel P/N 100636-1. The requirement section (1) mandates that these cast steel compressor wheels be replaced with P/N 4503164, 4504174, or M4504174, and similarly, section (2) mandates that wrought steel compressor wheels be replaced with the same part numbers. The compliance section outlines the specific cycle limits for these replacements based on the number of cycles since new. The AD imposes obligations on the owners and operators of the affected aircraft to ensure that the specified compressor wheel replacements are carried out in accordance with the directive. For cast steel compressor wheels, if the aircraft has accumulated more than 2,350 cycles since new, the replacement must occur within 250 cycles in service (CIS) after the directive's effective date, or before reaching 2,600 cycles. If the aircraft has fewer than 2,350 cycles since new, the replacement must occur before reaching 2,600 cycles. For wrought steel compressor wheels, if the aircraft has accumulated more than 3,600 cycles since new, the replacement must occur within 500 CIS after the directive's effective date, or before reaching 4,100 cycles. If the aircraft has fewer than 3,600 cycles since new, the replacement must occur before reaching 4,100 cycles. Failure to comply with these obligations could result in uncontained compressor wheel failures and subsequent damage to the aircraft. The AD does not explicitly outline specific offences, penalties, or consequences for non-compliance. However, the directive is issued under the authority of the Civil Aviation Safety Authority (CASA) and failure to comply with an Airworthiness Directive can lead to enforcement actions under the Civil Aviation Act 1988. This could include fines, the grounding of non-compliant aircraft, and other regulatory actions. The exact penalties would depend on the specific circumstances of the non-compliance and any relevant regulations or acts under which CASA can take action.