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CUSTOMER SERVICES DIRECTORATE 2 ROND POINT EMILE DEWOITINE 31700 BLAGNAC FRANCE TELEPHONE + 33 (0)5 61 93 33 33
ALERT OPERATORS TRANSMISSION - AOT AOT ref: A71L018-21 Rev 00 Page 1 of 5 Date: 29-MAR-2021 © AIRBUS S.A.S. 2021. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT SUBJECT: ATA 71 – A330 Trent 700 Engine - Inspection of the Hydraulic Pressure Switch Harnesses AIRCRAFT TYPE: A330 OUR REF.: A71L018-21 Rev 00 dated 29-MAR-2021 EFFECTIVITY DATE: 11th of April
1. AIRCRAFT AFFECTED A330 aircraft fitted with Trent-768, Trent-772, Trent 772B and Trent-772C engines affected (list available in the NMSB Ref.1).
A330 aircraft fitted with Trent-768, Trent-772, Trent 772B and Trent-772C engines non-affected (not listed in the NMSB Ref.1). AOT application is requested before affected engines can be fitted on these aircraft.
2. REFERENCED DOCUMENTATION
2.1 APPENDIX None
2.2 REFERENCES Ref.1 – Rolls-Royce NMSB 71-AK677 – Engine – Inspection of the pressure switch hydraulic harnesses Ref.2 – AMM TASK 71-13-00-010-805-A - Open the Fan Cowl Doors Ref.3 – AMM TASK 78-31-00-040-805-A - Deactivation of the Thrust Reverser for Maintenance Ref.4 – AMM TASK 29-31-00-710-803-A – Operational Test of the Hydraulic-System Pressure Indicating Ref.5 – Airbus OIT 999.0097/16 Rev 00, 08th Sep 2016.
3. REASON
3.1 FACTS One A330 family aircraft equipped with Trent 700 engines experienced an In-Flight Turn Back due to loss of Green and Blue hydraulic systems in cruise.
On the Green hydraulic system, HYD G ENG 2 PUMP LO PR and G SYS LO PR ECAM warnings were triggered leading to Green hydraulic systems loss.
On the Blue hydraulic system, HYD B ENG 1 PUMP LO PR ECAM warning was triggered, and the Flight Crew selected the Blue EDP OFF as per FCOM procedure.
Subsequent inspections of engine 1 revealed that during a previous maintenance shop visit, and following
ALERT OPERATORS TRANSMISSION - AOT AOT ref: A71L018-21 Rev 00 Page 2 of 5 Date: 29-MAR-2021 © AIRBUS S.A.S. 2021. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT hydraulic harnesses partial re-routing, the Blue and Green EDP pressure switch electrical connectors (4001JG2-A and 4001JG1-A) were cross connected.
This swap had as a consequence to declare the Blue hydraulic system faulty in flight when in reality the Green hydraulic system was failed with low pressure. According to the incorrect ECAM Warning HYD B ENG 1 PUMP LO PR, the flight crew followed the FCOM procedure leading to depressurize the blue hydraulic system while the Green system was actually faulty. As a consequence, two hydraulic systems were lost in flight (Blue and Green) instead of only one (Green).
3.2 CONSEQUENCES The Green hydraulic system is supplied by two EDPs. One is installed on engine 1 and one is installed on engine 2. Blue hydraulic system is supplied by one EDP installed on engine 1. Yellow hydraulic system is supplied by one EDP fitted on engine 2. Refer to Figure 1.
In case of EDP pressure switches being cross connected on one engine, the loss of one hydraulic system will result in incorrectly triggering the EDP low pressure condition ECAM warning on the second EDP installed on the same engine.
An incorrect hydraulic EDP low pressure ECAM warning (HYD G ENG 1 (2) PUMP LO PR, HYD Y ENG 2 PUMP LO PR and/or HYD B ENG 1 PUMP LO PR) can lead to setting to OFF the healthy hydraulic pump and not the faulty pump. The consequence is the loss of the two hydraulic systems on one engine while only one is faulty.
The worst case scenario (which is remote and not reported today) would occur with a Green Hydraulic System loss and a hydraulic EDP pressure switch harnesses cross connection on both engines. ECAM warning Hydraulic Low Pressure would be erroneously displayed for Blue and Yellow Hydraulic EDPs.
This can lead to setting OFF the blue and yellow hydraulic systems, resulting in the loss of all hydraulic systems (Green which is failed, Blue and Yellow set to OFF). The Figure 1 hereafter details this scenario.
Figure 1 - Two engines cross wired and loss of green system
ALERT OPERATORS TRANSMISSION - AOT AOT ref: A71L018-21 Rev 00 Page 3 of 5 Date: 29-MAR-2021 © AIRBUS S.A.S. 2021. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT
3.3 AIM The aim of this AOT is to require the inspection of the hydraulic pump pressure switch harnesses on all Trent 700 engines defined in the NMSB Ref.1. This inspection will remove potential cross-connections of the engine mounted hydraulic harnesses and prevent associated incorrect display in the cockpit. If harness routing and/or pressure switch connections are found incorrect, this AOT includes instructions to rectify the harness installation.
4. SHORT TERM ACTION NOTE: This AOT is classified mandatory or expected to be classified mandatory by an Airworthiness Directive (AD). The accomplishment instructions marked as Required for Compliance (RC) must be done to comply with the AD. “RC” is indicating these paragraphs accordingly.
NOTE: The accomplishment instructions of this AOT include procedures given in other documents or in other sections of the AOT. When the words ’refer to’ are used and the operator has a procedure accepted by the local authority he belongs to, the accepted alternative procedure can be used. When the words ’in accordance with’ are used then the given procedure must be followed.
NOTE: The access and close-up instructions, not comprising return to service tests, in this AOT do not constitute or affect the technical intent of the AOT. Operators can therefore, as deemed necessary, omit or add access and/or close-up steps to add flexibility to their maintenance operations as long as the technical intent of the AOT is met within the set parameters.
4.1 PLANNING AND MANPOWER
4.1.1 RC - ACCOMPLISHMENT TIMESCALE Do the inspection of the hydraulic pump pressure switches installation following instructions from Rolls- Royce NMSB Ref.1 on all Trent 700 engines defined in the NMSB Ref.1.
The inspections of the hydraulic pressure switch harnesses are to be done within 1000 Flight Hours and not after the 30th of June.
For Aircraft parked and / or under long term storage with no operation within 3 months after release of this AOT, inspection and harness re-routing – if needed - can be postponed to the end of the parking / long term storage period and prior to returning to flight.
In case the procedure detailed in RR NMSB Ref. 1 is performed on both engines at the same time, Airbus recommends all Operators to take into consideration the best practices for simultaneous maintenance on redundant items detailed in Airbus OIT Ref. 5.
4.1.2 MANPOWER Once access to the engine is obtained, the estimated time to perform the inspection is 0.5 Man-Hour per engine.
ALERT OPERATORS TRANSMISSION - AOT AOT ref: A71L018-21 Rev 00 Page 4 of 5 Date: 29-MAR-2021 © AIRBUS S.A.S. 2021. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT The time to perform the harnesses removal and installation, in case incorrect wiring is identified, is estimated to be up to 8 Man-Hours per engine.
4.2 DESCRIPTION
4.2.1 ACCESS To get/close access to the engine, perform the procedures as per Airbus AMM Ref.2 and Ref.3.
4.2.2 RC - INSPECTION REQUIREMENTS The hydraulic pressure harnesses inspections have to be performed as per Rolls-Royce NMSB Ref.1.
NOTE: When an engine is installed on an aircraft, the AMM TASK 71-00-00-400-805-A - Installation of the Demountable Power Plant has to be followed. This task will be updated at AOT release date to include the AMM TASK 29-31-00-710-803-A – Operational Test of the Hydraulic-System Pressure Indicating. Refer to paragraph 4.2.3 for details regarding AMM Task Ref.4 application.
4.2.3 RC - FINDINGS If any incorrect harness routing and connections are observed during the inspection, rectify the installation by following the re-routing instructions in accordance with Rolls-Royce NMSB Ref.1 before next flight.
Rectification on engine 1:
If harness routing rectification was performed on engine 1, a test of the hydraulic system as per the AMM Task 29-31-00-710-803-A subtask 29-31-00-710-051-D Ref.4, as detailed in the RR NMSB Ref.1 is required. Apply the AMM Task Ref.4 procedure for engine 1 Green Hydraulic pressure switch first and then for engine 1 Blue Hydraulic pressure switch secondly, one at a time and check correct system reaction after each step of the procedure. Do not apply the procedure for both circuits at the same time.
Rectification on engine 2:
If harness routing rectification was performed on engine 2, a test of the hydraulic system as per the AMM Task 29-31-00-710-803-A subtask 29-31-00-710-051-D Ref.4, as detailed in the RR NMSB Ref.1 is required. Apply the AMM Task Ref.4 procedure for engine 2 Green Hydraulic pressure switch first and then for engine 2 Yellow Hydraulic pressure switch secondly, one at a time and check correct system reaction after each step of the procedure. Do not apply the procedure for both at the same time.
For engines off-wing, Airbus requires to perform this test at the engine installation on-wing.
Report all findings of incorrect harness routing or pump pressure connection to both Airbus and Rolls- Royce.
For any finding not covered by this AOT, please contact Rolls-Royce prior to the next flight for instructions.
4.3 SPARES AND TOOLING No specific spare parts or tooling are required to perform this inspection.
ALERT OPERATORS TRANSMISSION - AOT AOT ref: A71L018-21 Rev 00 Page 5 of 5 Date: 29-MAR-2021 © AIRBUS S.A.S. 2021. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT Nevertheless, if specific spare parts are required following this AOT inspection, please contact Airbus or Rolls-Royce for further assistance.
5. FURTHER INFORMATION
5.1 FOLLOW-UP PLAN This inspection is expected to be mandated by the Airworthiness Authorities.
Further technical follow-up, if needed, will be provided through Airbus In-Service Information (ISI) ref.
71.00.00078.
5.2 IMPACTED DOCUMENTATION AMM TASK 71-00-00-400-805-A - Installation of the Demountable Power Plant AMM TASK 29-11-17-400-803-A - Installation of the Engine-Pump Pressure Switch AMM TASK 29-11-17-400-804-A - Installation of the Engine-Pump Pressure Switch AMM TASK 29-31-00-710-803-A – Operational Test of the Hydraulic-System Pressure Indicating
6. AOT APPROVAL The technical content of this document is approved under the authority of the DOA ref.EASA.21J.031.
7. REPORTING Questions about this AOT are to be addressed to Airbus Customer Services through TechRequest on Airbus World, selecting Maintenance & Engineering Domain, Engineering Support Section and ATA
71-00.
As per latest reporting policy (Ref to OIT 999.0018/16), inspection results (with or without findings) are to be addressed to Airbus Customer Services through the generic e-mail address:
inspection.results@airbus.com.
Best Regards, Christian FREMONT
VICE PRESIDENT ENGINEERING SUPPORT
CUSTOMER SERVICES Pilar ALVAREZ