Narrative:

At FL350 we experienced the loss of our yellow hydraulic system reservoir. We isolated the system, declared an emergency, and eventually diverted to chicago a few mins after I turned back toward pit, my departure point. The descent, approach and landing were uneventful. Upon clearing the runway, I instructed the first officer to terminate the emergency, and I taxied the aircraft to the gate. No injuries or aircraft damage were sustained. The aircraft was repaired overnight and returned to revenue service the next day. I elected to declare an emergency and divert because of the potential seriousness of losing a main hydraulic system. After discussing possible courses of action with dispatch and my crew, including an airbus qualified air carrier check airman who I requested come forward and occupy my jump seat, we concluded the most suitable divert location was chicago, which lay approximately 135 NM northwest of my position. Chicago offered us maintenance, passenger rebooking, large choice of runway and approach selections, plus it was relatively close. The crew was unaware we developed a leak until the reservoir lever was below usable level. We were unable to prevent further loss due to the nature of the leak -- a seal in a fitting of a line supplying hydraulic fluid to the autobrake system. Our only recourse was to land and make the necessary repairs.

Related reports:

Google
 

Original NASA ASRS Text

Title: AN AIRBUS 319 IN CRUISE AT FL350 DECLARED AN EMER AND DIVERTED DUE TO LOSS OF YELLOW SYS HYD PRESSURE AND QUANTITY CAUSED BY A FAILED AUTOBRAKE MODULE SEAL.

Narrative: AT FL350 WE EXPERIENCED THE LOSS OF OUR YELLOW HYD SYS RESERVOIR. WE ISOLATED THE SYS, DECLARED AN EMER, AND EVENTUALLY DIVERTED TO CHICAGO A FEW MINS AFTER I TURNED BACK TOWARD PIT, MY DEP POINT. THE DSCNT, APCH AND LNDG WERE UNEVENTFUL. UPON CLRING THE RWY, I INSTRUCTED THE FO TO TERMINATE THE EMER, AND I TAXIED THE ACFT TO THE GATE. NO INJURIES OR ACFT DAMAGE WERE SUSTAINED. THE ACFT WAS REPAIRED OVERNIGHT AND RETURNED TO REVENUE SVC THE NEXT DAY. I ELECTED TO DECLARE AN EMER AND DIVERT BECAUSE OF THE POTENTIAL SERIOUSNESS OF LOSING A MAIN HYD SYS. AFTER DISCUSSING POSSIBLE COURSES OF ACTION WITH DISPATCH AND MY CREW, INCLUDING AN AIRBUS QUALIFIED ACR CHK AIRMAN WHO I REQUESTED COME FORWARD AND OCCUPY MY JUMP SEAT, WE CONCLUDED THE MOST SUITABLE DIVERT LOCATION WAS CHICAGO, WHICH LAY APPROX 135 NM NW OF MY POS. CHICAGO OFFERED US MAINT, PAX REBOOKING, LARGE CHOICE OF RWY AND APCH SELECTIONS, PLUS IT WAS RELATIVELY CLOSE. THE CREW WAS UNAWARE WE DEVELOPED A LEAK UNTIL THE RESERVOIR LEVER WAS BELOW USABLE LEVEL. WE WERE UNABLE TO PREVENT FURTHER LOSS DUE TO THE NATURE OF THE LEAK -- A SEAL IN A FITTING OF A LINE SUPPLYING HYD FLUID TO THE AUTOBRAKE SYS. OUR ONLY RECOURSE WAS TO LAND AND MAKE THE NECESSARY REPAIRS.

Data retrieved from NASA's ASRS site as of July 2007 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.