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.