Narrative:

Passing through FL270; received hydraulic Y low quantity ECAM. Accomplished ECAM procedures. Noted 95% of fluid gone and accumulator pressure dropping slowly. Contacted maintenance and dispatch and all concurred return to ZZZ most prudent course. First officer coordination return ZZZ during call. We completed flight manual items including overweight landing checklist. Dispatch backed up our calculations. Return ZZZ uneventful with touchdown about 4000 pounds overweight. Touchdown less than 200 FPM and no inspection required. Maintenance advised us confirmed yellow hydraulic quantity zero due unknown failure.

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Original NASA ASRS Text

Title: AN A320 'HYD Y LO QTY' ECAM ANNUNCIATED. AN EMER WAS DECLARED WITH A RETURN TO LAND OVERWEIGHT.

Narrative: PASSING THROUGH FL270; RECEIVED HYD Y LOW QUANTITY ECAM. ACCOMPLISHED ECAM PROCS. NOTED 95% OF FLUID GONE AND ACCUMULATOR PRESSURE DROPPING SLOWLY. CONTACTED MAINT AND DISPATCH AND ALL CONCURRED RETURN TO ZZZ MOST PRUDENT COURSE. FO COORD RETURN ZZZ DURING CALL. WE COMPLETED FLT MANUAL ITEMS INCLUDING OVERWT LNDG CHKLIST. DISPATCH BACKED UP OUR CALCULATIONS. RETURN ZZZ UNEVENTFUL WITH TOUCHDOWN ABOUT 4000 LBS OVERWT. TOUCHDOWN LESS THAN 200 FPM AND NO INSPECTION REQUIRED. MAINT ADVISED US CONFIRMED YELLOW HYD QUANTITY ZERO DUE UNKNOWN FAILURE.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.