Federal Register of Legislation - Australian Government

Primary content

AD/MAKILA/9 Airworthiness Directives/Pt 106 — Engines as made
Engine Control Unit - Comparator/Selection Board
Administered by: Infrastructure and Transport
Exempt from sunsetting by the Legislative Instruments Act 2003 s 54(2) item 9
Registered 07 Jun 2007
Tabling HistoryDate
Tabled HR13-Jun-2007
Tabled Senate13-Jun-2007
Date of repeal 20 Jun 2008
Repealed by AD/MAKILA/9 Amdt 1 - Engine Control Unit - Comparator/Selection Board



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.

Turbomeca Turbine Engines - Makila Series


Engine Control Unit - Comparator/Selection Board




Makila 1A and Makila 1A1 turbo-shaft engines.


Note 1:  These engines are known to be installed in, but not limited to, AS 332 B, B1, C, C1, F1, L and L1 Super Puma helicopters.


Replace the Engine Control Unit (ECU) Selector-Comparator board with one incorporating Turbomeca modification TU250.  Replacement of the Selector-Comparator board and return of the Modification Compliance Certificate to Turbomeca must be performed in accordance with Turbomeca Mandatory Service Bulletin 298 73 0250 dated 23 March 2007.


Note 2:  A post-TU250 ECU and a pre-TU250 ECU can be installed in the same helicopter.


Note 3:  EASA AD 2007-0144 refers.


Before 30 June 2008.


This Airworthiness Directive becomes effective on 5 July 2007.


Modification TU203, applicable to Makila 1A and Makila 1A1 engines, introduced a control system backup law that fixes N1 (gas generator speed) at 65% when at least two of the three N2 (power turbine speed) signals are lost.  The intent is to limit the maximum speed attainable by the power turbine in the event of a failure of the shaft between the Engine and the Main Gearbox that could result in collateral damage to the N2 speed probes.

Recent occurrences of 65% N1 backup activation remain unexplained despite detailed investigation.  Although not substantiated, it is postulated that the events may have been due to corruption of the engine N2 speed signals by short perturbations, for example by EMI.  The potential therefore exists for a hazardous condition in which both engines on the same helicopter are simultaneously affected.





This Airworthiness Directive requires a hardware modification to the ECU that allows recovery from the 65% backup mode if the loss of N2 speed signals is determined to be temporary.  The modification applies to the Selector-Comparator board in the ECU.

Charles Lenarcic
Delegate of the Civil Aviation Safety Authority

25 May 2007