Ad/APU/19 - Micorturbo - Overspeed Protection Channel (Cth)
AIRWORTHINESS DIRECTIVE
For the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.001(1) of CASR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.
Auxiliary Power Units
| AD/APU/19 | Micorturbo - Overspeed Protection Channel | 11/2005 |
Applicability: | Auxiliary Power Unit (APU) SAPHIR 20 model 095. These APU’s are installed on AS332 and EC225 helicopters. |
Requirement: | Replace the existing ECU and the Drain Valve by an ECU and Drain Valve, modified in accordance with the instructions of MICROTURBO Alert Service Bulletin Note 1: The modified ECU includes the new EGT limit setting. Note 2: DGAC AD F-2005-146 EASA reference No 2005-6137 dated 9 August 2005 refers. |
Compliance: | Prior to the 31 December 2005. |
| This Airworthiness Directive becomes effective on 27 October 2005. | |
Background: | With the existing configuration, a certain failure could cause overspeed of the gas generator rotor resulting in uncontained burst of the turbine, liberating high-energy fragments. The occurrence that the high-energy fragments would be uncontained is considered a potentially dangerous situation which requires imperative corrective action. The purpose of the modification, which has been made mandatory, is to limit gas generator speed during acceleration towards overspeed by installation of a modified Electronic Control Unit (ECU) and Drain Valve. In addition, the modification also renders the EGT control function compliant with the certificated specifications. In operation, if EGT exceeds the certificated limit value, turbine blade shedding could occur. |
James Coyne
Delegate of the Civil Aviation Safety Authority
15 September 2005
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