AD/A330/54 Elevator Servocontrols (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.

Airbus Industrie A330 Series Aeroplanes

AD/A330/54 Elevator Servocontrols 12/2005 DM

Applicability:

AIRBUS A330-200 and A330-300 aircraft.

Requirement:

1.    Perform the periodic test of the elevator servo-loops in accordance with paragraph 4.2.1 of All Operator Telex (AOT) A330-27A3138 or later DGAC approved revision.

2.    Repeat the test defined in requirement 1 of this Airworthiness Directive (AD).

3.    If during the initial or repetitive inspection the test fails, carry out rectification as detailed in AOT A330-27A3138 or later DGAC approved revision, and report the findings to Airbus.

Note 1:  The additional periodic test detailed in this Directive does not supersede the existing CMR task.

Note 2:  DGAC AD UF-2005-171 EASA Approval No. 2005-6349 dated 3 October 2005 refers.

Compliance:

1.    Within 200 flight hours (FH), following the effective date of this AD.

2.    At intervals not exceeding 140 FH since the last check or eight days since last check whichever occurs first.

3.    Before further flight after the effective date of this AD.

This Airworthiness Directive becomes effective on 18 October 2005.

Background:

Each elevator is equipped with two servocontrols having three operating modes: Active mode, Damping mode, and Centering mode.  In normal operation each elevator is actuated by one servocontrol in Active mode, while the other is in Damping mode.

The mode change from Active to Damping is achieved by a Mode-Selector Spool Valve installed inside each servocontrol.  The position of this spool valve is commanded by a rod which slides through a guide.

Some operators have reported cases of elevator servocontrol removals due to warning “FCTL ELEV SERVO FAULT”.  During the shop repairs, some of these servocontrols installed at the active position were found with the guide broken.  The broken guides resulted in the inability for the affected servocontrols to change their operating mode.

The investigation has revealed that the root cause of the broken guides is a fatigue rupture induced by successive pressure cycles inside the servocontrol resulting in a progressive decrease of the tightening torque of the plug.

This situation, if not corrected, could result at worst in an unannounced loss of the elevator to the flight crew during take off roll phase, and in the extreme case reduce the controllability of the aircraft, which is potentially critical.

The aim of this AD is to mandate an additional periodic test of the elevator servo-loops in order to check the servocontrols ability to change their operating mode.

Jayaprakashan Ambali
Delegate of the Civil Aviation Safety Authority

12 October 2005