1) Several airlines have reported failures of the blue elevator servocontrol servovalves on various Airbus aircraft models. 2) The failures have resulted in loss of one elevator but the elevator remains controllable by the adjacent servocontrol. 3) Investigations found wear in the servovalve spring ball could induce a bias in the servoloop and lack of robustness in the standby servocontrol monitoring were contributing factors. A software update and servovalve design improvement are being implemented.

1. BLUE ELEVATOR SERVOCONTROL SERVOVALVE
FAILURES
Reference: 27.34.51.014 First Issue Date: 30-APR-2009 Last Publication Date:
18-JUN-2015 Status: Open
ATA: 27-34 A/C Type : A318 ; A319 ; A320 ; A321
Affected Part Number:
A68793-002
Supplier : MOOG CONTROLS LIMITED;
GOODRICH ACTUATION SYSTEMS SAS
FIN : 34CE3 ; 34CE4
Potential Impact: Operational Reliability
Linked Documentation: SB 27-1234 ; SB 27-1238 ; VSB 394512B-27-025 ; VSB 394512B-27-030
Engineering Support

2. First Issue Date: 30-APR-2009 Last Publication Date: 18-JUN-2015 Status: Closed
Fault Code/ECAM Warning: ELAC1-COM OR WIRING TO L B ELEV SERVO VLV 34CE3 ; ELAC2-COM
OR WIRING TO L G ELEV SERVO VLV 34CE1 ; ELAC1-COM OR WIRING TO R B ELEV SERVO VLV
34CE4 ; ELAC2-COM OR WIRING TO R Y ELEV SERVO VLV 34CE2 ; ELAC1-COM OR WIRING TO L
B ELEV SERVO VLV 34CE3 ; ELAC2-COM OR WIRING TO L G ELEV SERVO VLV 34CE1 ; ELAC1-COM
OR WIRING TO R B ELEV SERVO VLV 34CE4 ; ELAC2-COM OR WIRING TO R Y ELEV SERVO VLV
34CE2
Issue Description
An increasing number of Airlines have reported the following failures:
- F/CTL ELAC 1 PITCH FAULT associated with ELAC1 - COM OR WIRING TO L(R)
B ELEV SERVO VLV 34CE3(4)
- F/CTL ELEV SERVO FAULT associated with ELAC1 - COM OR WIRING TO L(R) B
ELEV SERVO VLV 34CE3(4) or SEC1 - COM OR WIRING TO L(R) B ELEV SERVO
VLV 34CE3(4) or L(R) B ELEV SERVO VLV 34CE3(4)
In almost all the cases, servovalves (or complete servocontrol) replacements
have enabled to fix the fault.
Consequence
Loss of one elevator servocontrol, which remains in damping mode. The elevator
is still controlled with the adjacent servocontrol.
Investigation Status
The tests performed at Airbus laboratory with removed servocontrol or
servovalves did not allow to reproduce the failure as experienced by airlines on
aircraft. Nevertheless, the examinations performed by UTAS and Moog on
several servovalves have shown non-conform wear of the spring ball, which
induces a bias in the servoloop. Considering the results, such a defect alone, out
of the aircraft environment, does not lead to the system fault detection and
other contributors to the bias monitored by ELAC have been considered.
ELAC functioning has been reviewed and specifically the servovalve monitoring
on blue system by ELAC 1.
- The inhibition of the servovalve natural bias compensation (as per today
design) on the blue system has been identified as a potential contributing factor
to the fault detection.
- A drift of setting of the standby servocontrol LVDT with regard to the active
one was suspected to be a contributor to the bias in the servoloop. However,
recent flight tests on MSN001 and in lab have shown that the servocontrols
misrigging did not permit to trigger the monitoring.

3. To date, two main contributors are considered:
- Lack of robustness of the stand-by servocontrol monitoring (L B and R B
servocontrols) performed by the ELAC1 is considered as the primary contributor
to the servovalve fault detections.
- Wear of the servovalve spring ball part has been identified. This wear, notably
observed on servovalve Moog PN A68793-002, leads to a biais in the elevator
servoloop, thus contributing to the servovalve fault detection if combined with
the stand-by servocontrol monitoring described above.
Moog will provide the shop report of the servovalves returned for repair upon
request by the customer (to be mentioned in the PO).
Mitigation / Interim Plan
In case of F/CTL ELEV SERVO FAULT associated with ELAC1 - COM OR WIRING
TO L(R) B ELEV SERVO VLV 34CE3(4) or SEC1 - COM OR WIRING TO L(R) B
ELEV SERVO VLV 34CE3(4) or L(R) B ELEV SERVO VLV 34CE3(4)x, the
servovalve shall be replaced directly.
In case of "F/CTL ELAC 1 PITCH FAULT" ECAM warning triggered ON GROUND
associated with ELAC1 - COM OR WIRING TO L(R) B ELEV SERVO VLV 34CE3(4),
an ELAC reset can clear the fault if it is due to particular conditions (cold
temperature, surface position at engine start).
Nevertheless, if the same fault reoccurs within the next two days, the
replacement of the servovalve is necessary to fix the fault.
Maintenance Information
Replace, as a first action, the servovalve (LRU) instead of the complete
servocontrol.
It is even advised to replace the servovalve before replacing the ELAC.
Repercussion on A/C Dispatch
"F/CTL ELEV SERVO FAULT" : No dispatch.
"F/CTL ELAC 1 PITCH FAULT" : Refer to MMEL 27-93-01.
Solution
1- ELAC software modification:
An improvement of the elevator stand-by servocontrol monitoring has been
developed. This will avoid numerous detections on blue actuators.
The ELAC monitoring modification is available in the ELAC standard L97 which is
compatible with sharklet (L95 standard being cancelled).

4. The In Service Evaluation (ISE) has been successfully completed. A fleetwide
ELAC L97 retrofit has been launched from June 2014.
This retrofit is supported by a RIL (Retrofit Information Letter) and associated
Airbus SB A320-27-1234 (for ELAC B-dl with dataloading capability) and A320-
27-1238 (for ELAC B without dataloading capability).
ELAC B / B-dl L97 retrofit has been superseded by ELAC L97+ retrofit
from March 2015.
Since March 2015, the ELAC A/A' are also replaced by ELAC B-dl with
L97+ operational software loaded. Refer to RIL for exact commercial
conditions.
2- Servovalve improvement:
Studies at UTAS and Moog (servovalve supplier) are still in progress to correct
the main identified failure modes affecting the spool position: null position bias
out of tolerance, loose ball fit and LVT faults.

5. Retrofits Monitoring
First Issue Date: 04-DEC-2014 Last Publication Date: 04-DEC-2014 Status:
Open
Retrofit Information Letter: YES

6. This modification is subject to an AIRBUS Monitored Retrofit.
Airbus Retrofit Information Letter is available.
It details retrofit process and material ordering.
For a complete list of monitored retrofits applicable to your fleet, please contact
monitored.retrofit@airbus.com.
© Airbus SAS, 2014. All rights reserved. Confidential and proprietary document.The technical
information provided in this article is for convenience and information purposes only. It shall in
no case replace the official Airbus technical or Flight Operations data which shall remain the sole
basis for aircraft maintenance and operation. These recommendations and information do not
constitute a contractual commitment, warranty or guarantee whatsoever. They shall not
supersede the Airbus technical nor operational documentation; should any deviation appear
between this article and the Airbus or airline's official manuals, the operator must ensure to
cover it with the appropriate document such as TA, FCD, RAS. Access to WISE is supplied by
Airbus under the express condition that Airbus hereby disclaims any and all liability for the use
made by the user of the information contained in WISE. It shall be used for the user's own
purposes only and shall not be reproduced or disclosed to any third party without the prior
consent of Airbus.