Date: 201205
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Weather elements / visibility: Fog
Light: Daylight
Aircraft: A320
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Gear Down Lock
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Airframe; Maintenance Powerplant
Human factors: Communication Breakdown; Confusion; Troubleshooting; Training / Qualification; Situational Awareness
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted; General Maintenance Action
Contributing factors: Company Policy; Equipment / Tooling; Human Factors; Chart Or Publication; Aircraft; Incorrect / Not Installed / Unavailable Part; Weather; Procedure; Manuals
Primary problem: Manuals

Narrative: Aircraft X; an A320; on Final into ZZZ; selected 'Gear Down' and lost Green System hydraulics. Aircraft was towed from runway to Gate. A [hydraulic] leak was noted at the left Main Landing Gear (MLG) Down Lock actuator flex hose; inboard of the two flex lines. A replacement line was shipped in from ZZZ1 and installed per Aircraft Maintenance Manual 32-11-22 'Installation of Lock Stay' actuator hose. After installation; hydraulics was serviced to required level and ran engines and operated flight controls to move hydraulics though Green System. A Functional Test was required AMM 32-31-00; but thought brace tool was gear safety collars and the Functional Test was completed. Green System hydraulics was again serviced to proper level. Aircraft released to service. [I] was called by our ZZZ Maintenance Manager that Aircraft X had lost Green System hydraulics's and was diverting to ZZZ2. [Realized] I misinterpreted a step in the Functional Test. Then looked into what this brace tool was. [Recommend]: 1) Confer with more Aviation Maintenance Technicians AMTs on understanding [AMM] terminology. 2) This job; I have seen been accomplished and no problems occurred as this. 3) When I selected the AMM reference; AMM 32-31-00-710; this reference was right below the one I should have selected; AMM 32-31-00-720.

Callback: Reporter stated he has 29-years of Mechanic experience with two airlines. Many of the misunderstandings in reading Airbus Aircraft Maintenance Manuals (AMM) involve Airbus terminology compared to Boeing AMMs. The purpose of the lock stay brace tool was not explained in the Airbus AMM. Only that a procedure had to be performed involving the Lock Stay Down Lock actuator because the hydraulic hose to the down lock actuator had broken away from the actuator in flight where the flex line attach fitting connects to the hose. The separated hose caused an excessive loss of Green System hydraulic fluid.Reporter stated their Line Station does not have any facilities; no Hangar to do gear swings and did not have a brace tool to accomplish cycling of the lock stay down lock actuator after they had replaced the broken flex hose. He selected one of two alternate procedures in the Airbus AMM that allows for installing gear pins; 'slugging' the main gear and moving the gear handle up and down to check for hydraulic pressure and any leaks at the actuator hose fittings on the down lock actuator; without having to do an actual gear swing. Unfortunately he selected the wrong alternate procedure. Reporter stated that since the broken flex line caused the loss of hydraulic Green System hydraulic fluid; Airbus requires a 'priming' of the Green System by actuating the down lock actuator numerous times with the brace tool installed; which was not done since they did not have a brace tool at their Station. The same hose seems to break or leak fairly often; probably due to the constant flexing of the hose at the actuator connection and the fact that the hose is exposed when the gear is extended. Although they did operate the gear doors; flight controls; run the engines and service the Green System to required levels; the A320 Green System quantity dropped and the flight diverted halfway to their destination. The diversion was not due to actual hydraulic fluid loss. The Green System just required more fluid to replenish the System. They now have a brace tool at their Line Station.



Synopsis: A Line Mechanic reports that misunderstandings of terminology used in Airbus Aircraft Maintenance Manuals (AMM) compared to Boeing AMMs and the lack of an Airbus Brace Tool led to an A320 diversion due to low Green System hydraulic fluid. A hydraulic flex hose to the Lock Stay; Down Lock actuator on the left Main Gear had broken on a previous flight.