Date: 201209
Local time of day: 0001-0600
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Night
Aircraft: A330
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance
Detector: Automation Aircraft Other Automation
When detected: In-flight
Result: Flight Crew Returned To Departure Airport; General Declared Emergency; General Maintenance Action
Contributing factors: Aircraft; Procedure
Primary problem: Aircraft

Narrative: Our aircraft for the flight was towed from the maintenance hangar; and arrived at the departure gate approximately two hours after scheduled departure time. We learned after the event that Maintenance had had the aircraft 'most of the day;' and had replaced the nose landing gear actuator. Push-back; engine start; taxi out; takeoff; climb; and initial cruise were normal. Approximately one hour into the flight and at level cruise; the Master Caution activated and ECAM indicated a Green Hydraulic System leak. Following our non-normal procedures we turned off the pumps pressurizing the Green System thereby deactivating the Green Hydraulic System. We were in ARTCC airspace at the time and informed the Controller that we had a hydraulic problem; needed to return to our departure airport; were not declaring an emergency at that time but would do so when entering Approach Control airspace. The Controller issued an initial heading; and then subsequently issued a new clearance directly to an intersection on a STAR to the airport. The Captain called the Lead Flight Attendant to the cockpit and briefed her on our situation; time remaining; etc. I made the PA to the passengers that we had a mechanical issue that required our return to our departure airport. When the Relief Pilot returned the Captain directed him to establish SATCOM communications with Dispatch; Maintenance Control and Airport Operations. In addition he was to contact our departure ATC facility by VHF to let them know of our return; that we would be an emergency; and to request CFR to be standing by. As a result of the loss of the Green Hydraulic System; among a lengthy list of inoperative systems; we would not have nose wheel steering or normal brakes; slats/flaps would be slow to extend and we would have to gravity extend the landing gear. Enroute we reviewed and briefed the QRH procedures for the gravity gear extension including field landing length requirements and approach speed increases; developed a plan for when and how we would configure the aircraft for approach and landing; discussed that the gear doors would be open; and whether they would drag on the runway. We also reviewed and briefed our STAR and expected ILS approach. Finally; we planned to stop on the runway; shut the engines down; and be towed to the passenger terminal. The Captain made a PA explaining that we had a hydraulic problem; that they may hear sounds and noises that they may not be accustom to; the landing would be normal; airport emergency vehicles follow and surround our aircraft; and that we would be towed back to the gate. When in communication with our destination Center we were advised the airport had been informed; and that 'they were ready.' When we switched to Approach Control we declared the emergency and received vectors for the ILS. We extended the gear in accordance with QRH procedures so that we were fully configured prior to glide slope intercept. The landing was smooth; in the touch down zone and rollout was normal as we stopped in the first three quarters of the runway. We shut down the engines; and were shortly thereafter towed to gate. The flight was subsequently canceled. While we were waiting for the hookup and tow I selected the Hydraulic page on the System Display (SD). The Green System showed full and normal quantity. Once at the gate a Mechanic came in and said that the system had been 'over-serviced.'




Synopsis: An A330 returned to its departure airport after receiving a Green Hydraulic System Leak ECAM message. Maintenance later advised the system had been 'over serviced'