AOT_27A3185_00[1].txt

ALL OPERATORS TELEX - ALL OPERATORS TELEX

SUBJECT: ATA 27 – SPOILER SERVO CONTROLS – LOSS OF THE HYDRAULIC LOCKING 

FUNCTION

OUR REF: AOT A330-27A3185 dated 04 January 2012

1. AIRCRAFT AFFECTED

All A330-300 in-service aircraft fitted with MZ-type Spoiler Servo Controls 

(SSC), Part Number (PN) MZ4339390-12 or PN MZ4306000-12.

2. REFERENCED DOCUMENTATION

- Ref.1: Liebherr Component Maintenance Manual (CMM) 27-64-52 Figure 4 

Item 210 – Blocking Valve

- Ref.2: Liebherr CMM 27-64-52 Figure 4 Item 140 – Maintenance Operator 

Mechanism

- Ref.3: Liebherr CMM 27-64-52 Figure 4 Item 190 – Seal

- Ref.4: Airbus Service Bulletin (SB) A330-27-3110 - Flight Controls - 

Spoiler - Introduce operator mechanism cover

- Ref.5: EASA Airworthiness Directive (AD) 2008-0160 – Flight Controls – 

Spoiler Servo Control Maintenance Cover – Identification / Modification

- Ref.6: FAA AD 2009-18-20

- Ref.7: Aircraft Maintenance Manual (AMM) Task 27-64-00-710-802 – 

Operational Test of the Hydraulic Locking Function on the Spoiler Servo 

Control

- Ref.8: AMM 27-64-52 PB 401 – Servo Control – Spoiler 2,3,4,5,6 – Removal 

/ Installation

- Ref.9: AMM 27-64-51 PB 401 – Servo Control – Spoiler 1 – Removal / 

Installation 

- Ref.10: Master Minimum Equipment List (MMEL) item 29-09-01 – HYD G(B)(Y) 

ELEC PUMP FAULT Alert, dated 16 December 2011

- Ref.11: MMEL item 29-20-04 – Yellow Auxiliary Hydraulic power 

(Electrical Pump), dated 16 December 2011

- Ref.12: Airbus Reporting Sheet RS-SEEL6-2011-686000

- Ref.13: Liebherr-Aerospace Information Notice reference AER/CS/1107-13

- Ref.14: Airbus Technical Follow Up (TFU) 27.64.00.013 – Spoiler SC MZ 

type – Loss Of Hydraulic Locking Function

3. REASON

3.1. FACTS

Two operators have reported several spoilers not remaining in the retracted 

position after manual depressurization of the corresponding hydraulic 

circuit during test flights.

Subsequent checks on ground confirmed that, for each affected spoiler 

surface:

- The spoiler was fitted with one MZ-type SSC (PN MZ4339390-12 or PN 

MZ4306000-12)

- The maintenance operator mechanism of the SSC was confirmed in the 

‘O’ (Operation) position (hydraulic locking function operative). 

Nevertheless, the spoiler surface could be manually extended.

3.2. SYSTEM DESCRIPTION

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Each aircraft is fitted with six pairs of spoilers, identified from 

position 1 (inboard) to 6 (outboard). 

Each SSC is controlled by a single flight control computer and supplied by 

one hydraulic circuit:

- Positions 1 (13CS1/13CS2) and 5 (17CS1/17CS2) supplied by Green (G) 

circuit.

- Positions 2 (14CS1/14CS2) and 3 (15CS1/15CS2) supplied by Blue (B) 

circuit.

- Positions 4 (16CS1/16CS2) and 6 (18CS1/18CS2) supplied by Yellow (Y) 

circuit.

SSCs installed in position 1 are not interchangeable with the remaining 2 

to 6 SSC positions since the length of the stroke is different.

Each SSC is fitted with a blocking valve ref.1, whose purpose is to ensure 

the hydraulic locking function. This prevents the extension of the spoiler 

in case of hydraulic depressurization:

- If the depressurization occurs when the spoiler is retracted, the SSC 

remains locked in position.

- If the depressurization occurs when the spoiler is extended, the 

blocking valve allows the retraction under aerodynamic loads.

In addition to the blocking valve ref.1, the SSC is fitted with a 

maintenance operator mechanism ref.2, which allows the de-activation of the 

locking function for maintenance purposes. 

During normal operation, the maintenance operator mechanism is set to the 

‘O’ (Operation) position, and the hydraulic locking function is operative. 

When the maintenance operator mechanism is set to the ‘M’ (Maintenance) 

position, the hydraulic locking function is de-activated, and the spoiler 

can be manually extended for maintenance purposes.

3.3. INVESTIGATIONS

3.3.1 SHOP FINDINGS

The investigation of the affected SSCs at Liebherr revealed that the loss 

of the hydraulic locking function was due to an internal leakage caused by 

a sheared seal ref.3. This seal is installed at the left end of the 

blocking valve ref.1.

3.3.2 PREVIOUS MODIFICATION

From 2008 to 2010, all MZ-type SSCs were modified to the current PN 

MZ4339390-12 (position 1) and PN MZ4306000-12 (position 2 to 6) as per 

ref.4 Airbus SB. This modification was mandated by ref.5 and ref.6 ADs.

3.3.3 SUSPECTED ROOT CAUSE

Most MZ-type SSCs were modified on-wing. During this on-wing modification, 

the ref.2 maintenance operator mechanism was removed, allowing a possible 

untimely migration of the ref.1 blocking valve out of its groove.

It is suspected that this untimely migration is the root cause for the 

sheared ref.3 seal events.

3.4. CONSEQUENCES

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As long as the corresponding hydraulic circuit is pressurized, this failure 

has no impact on the operation of the spoilers.

Nevertheless, in case of loss of the hydraulic locking function, the SSC is 

no longer able to remain in the retracted position in the event of a 

depressurization of the related hydraulic circuit. Therefore, the spoiler 

surface would extend up to the zero-hinge moment position, which mainly 

depends on the aircraft speed and on the Flap/Slat configuration.

This failure mode (internal leakage) cannot be detected by the flight 

control computers monitoring, and will remain as hidden until the 

associated hydraulic system is depressurized in flight. Should an untimely 

deflection in flight occur, this is announced to the crew via the ECAM 

warning F/CTL SPLR FAULT and the F/CTL Page on the System Display.

On ground, only the application of the test of the hydraulic locking 

function as per AMM ref.7 ensures the identification of faulty SSCs.

3.5. AIM

The aim of this AOT is to confirm the reliable functioning of the MZ-type 

SSCs currently installed on aircraft by means of a one-time test as per the 

new ref.7 AMM task.

It is anticipated that this AOT will be rendered mandatory by an EASA AD.

4. REQUIRED ACTION

4.1. PLANNING AND MANPOWER

The following corrective plan needs to be performed, as per paragraph 4.2, 

on all in-service affected aircraft:

- Within 90 days from receipt of this AOT:

* Identification of the concerned aircraft

* Test of the MZ-type SSC(s)

- In case of findings:

* Corrective actions to be accomplished before further flight on the 

SSCs related to the Blue hydraulic circuit

* Corrective actions to be accomplished within 24 months on the SSCs 

related to the Yellow and Green hydraulic systems

- Reporting within 30 days after accomplishment of the corrective 

actions

Spare units are not affected by the requirements of this AOT, because the 

hydraulic locking function is tested after any shop repair prior to EASA 

Form 1 issuance. 

Consequently:

- This AOT is only applicable to MZ-type SSC(s) already installed on 

in-service aircraft at the time of issuance of this AOT

- Aircraft which are not fitted with any MZ-type SSC are not affected 

by this AOT

The application of this AOT requires:

- Five man-hours and one hour elapsed time for the application of the 

ref.7 AMM task 

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- Additional three man-hours per SSC replacement.

4.2. DESCRIPTION

4.2.1. IDENTIFICATION/TEST OF AFFECTED AIRCRAFT

Within 90 days from receipt of this AOT:

1.Identify all aircraft fitted with at least one MZ-type SSC. Note that:

- PN MZ 4339390-12 is installed in positions 1 only.

- PN MZ 4306000-12 is installed in positions 2 to 6.

The two following procedures are approved for the identification:

- Use the data from operator approved records.

- Read the data by visual inspection on aircraft.

On aircraft which are not fitted with any MZ-type SSC, no further action 

is required by this AOT.

2.At each position fitted with a MZ-type SSC, perform the test of the 

hydraulic locking function as per ref.7 AMM.

4.2.2 CORRECTIVE ACTIONS

1.On Blue hydraulic circuit, for MZ-type SSC in position 2 and 3 (14CS1, 

14CS2, 15CS1, 15CS2):

- If the test is successful: No further action is required

- If the test fails: BEFORE FURTHER FLIGHT, interchange with a 

successfully tested unit from another circuit or replace with a spare 

part the faulty SSC(s), as per ref.8 AMM.

2.On Green hydraulic circuit, for MZ-type SSC in position 1 and 5 (13CS1, 

13CS2, 17CS1, 17CS2):

- If the test is successful: No further action is required

- If the test fails, or if an unsuccessfully tested SSC is installed in 

position 5 after interchange with Blue circuit: Within 24 months from 

AOT receipt, replace the faulty SSC(s) with a spare part as per ref.8 

or ref.9 AMM.

3.On Yellow hydraulic circuit, for MZ-type SSC in position 4 and 6 (16CS1, 

16CS2, 18CS1, 18CS2):

- If the test is successful: No further action is required

- If the test fails, or if an unsuccessfully tested SSC is installed 

after interchange with Blue circuit:

* Within 24 months from AOT receipt, replace the faulty SSC(s) with 

a spare part as per ref.8 AMM provided that, before replacement of 

the faulty SSC(s), the affected aircraft is not dispatched with 

the Yellow Electric Motor Pump (Y EMP) inoperative as per ref.10 

and ref.11 MMEL.

* Once all the faulty MZ-type SSC(s) are removed from the Yellow 

hydraulic circuit:

- Dispatch capability with the Y EMP inoperative is restored 

as per ref.10 and ref.11 MMEL.

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- Report the retrofit completion as per paragraph 4.2.3.

CAUTION: In order to prevent the installation of faulty units on nonaffected aircraft, only the interchange between positions of the same 

aircraft is acceptable.

ADVICE: Due to spare restriction (refer to 4.3): 

- It is acceptable to interchange with a unit successfully tested from 

another circuit of the same airplane, or to replace with a spare part, 

the faulty SSC(s) identified in positions 2 and 3 (14CS1, 14CS2, 15CS1, 

15CS2).

- It is acceptable to install or to keep installed unsuccessfully tested 

SSC(s) in positions 1, 4, 5, and 6. This approach allows:

* Up to two SSCs PN MZ4339390-12 without hydraulic locking capability 

per aircraft.

* Up to six SSCs PN MZ4306000-12 without hydraulic locking capability 

per aircraft.

4.2.3 DATA REPORTING

Step 1

For all aircraft fitted with at least one MZ-type SSC, within 30 days after 

accomplishment of the test as per paragraph 4.2.1, report the test results 

to the Airbus contact given in paragraph 7 by means of the Reporting Sheet 

ref.12.

Step 2

For all aircraft fitted with at least one unsuccessfully tested SSC on the 

Yellow hydraulic circuit, within 30 days after replacement of the faulty 

SSC(s) of the Yellow circuit as per paragraph 4.2.2, report the retrofit 

completion to the Airbus contact given in paragraph 7 by means of Reporting 

Sheet ref.12.

4.3. MATERIAL - TOOLING

No specific tooling is required for the inspection.

Concerning spares, Liebherr-Aerospace is currently facing a difficult 

supply chain situation on SSC PN 1386x and 1387x –current production 

standard– due to the fire damage suffered by Liebherr-Aerospace 

manufacturing plant in Brazil (ref.13).

Airbus and Liebherr-Aerospace will increase the spares stock, planned to 

reach 60 units by June 2012. Nevertheless, the current number of available 

spares remains insufficient to provide advanced spare parts to all 

operators prior to application of this AOT. 

Consequently, spare units will be supplied on AOG basis to operators if and 

only if more than six SSCs PN MZ4306000-12 are found faulty on the same 

aircraft and no spares are available at the operator’s warehouse.

Spare units have been positioned in Singapore, Europe and the USA in order 

to reduce the delivery lead-time. AOG orders should be addressed to:

Region: Europe, Africa, Middle East

Liebherr-Aerospace Lindenberg GmbH (LLI) 

Phone: +49 8381 46 4868

e-mail: spares.lli@liebherr.com 

24 Hrs/7 Days Spares AOG Hotline: +49 171 852 7304

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Region: Americas

Liebherr-Aerospace Saline, Inc (LSL)

Phone: +1 734 944 6378

e-mail: keith.turczyn@liebherr.com

24 Hrs/7 Days Spares AOG Hotline: +1 313 580 7262

Region: Asia-Pacific

Liebherr-Aerospace Singapore Pte. Ltd. (LSI)

Phone: +65 6265 2305

e-mail: charles.loke@liebherr.com

24 Hrs/7 Days Spares AOG Hotline: +65 9625 1607

According to the feedback as per paragraph 4.2.3, Airbus and LiebherrAerospace will establish a replacement plan of the faulty SSCs fitted on 

Green and Yellow hydraulic circuits.

Throughout this AOT campaign, loan units will be used to cover the spare 

needs during the turnaround time of the faulty SSC(s) in-shop repair. 

Process will be monitored by Airbus and planned in accordance with 

operators’ situation and availability. 

5. FURTHER ACTION

Follow-up of this AOT will be ensured by means of ref.14 TFU that will be 

issued by the end of January, 2012.

6. AOT APPROVAL

The technical content of this AOT has been approved under EASA Design 

Organization Approval EASA.21J.031.

The content of this AOT is expected to be rendered mandatory by the 

Airworthiness Authorities.

7. REPORTING / ACKNOWLEDGEMENT

Operators are requested to acknowledge receipt of this AOT within 48 hours 

after receipt to:

Mlle Laetitia BONNET, SEEL

Phone number: +33 (0)5 67 19 24 40

Fax number: +33 (0)5 61 93 32 73

E-mail: laetitia.bonnet@airbus.com

This acknowledgement can be made through the Airbus RCSR office when 

available.

Questions about the technical content of this AOT, and inspection results, 

with or without findings, are to be sent to Airbus Customer Services, 

Engineering and Technical Support, attention of:

Mr. Daniel LOPEZ FERNANDEZ, SEEL6

Phone number: +33 (0)5 61 93 04 52

Fax number: +33 (0)5 61 93 32 73

E-mail: daniel.lopez-fernandez@airbus.com

Best Regards,

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P.GOURDON

VICE PRESIDENT A330/A340 PROGRAMME

CUSTOMER SERVICES DIRECTORATE

If you do not need to receive AOT any more, or if other people in your 

organization need to be added to the distribution, please advise your 

Airbus Customer Services contact accordingly. 

AOT’s attachments (if any) can be downloaded from AirbusWorld via AirN@v / 

Engineering.

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