ACFT EQUIP PROBLEM CAUSES A SELECTION OF ANOTHER ARPT FOR LNDG BUT CLOSE TO DEST ARPT.

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SCHEDULED FLT FROM DEN-LGA. SHORTLY AFTER PASSING ORD AT FL330; A 'B' SYS LOW PRESSURE LIGHT ILLUMINATED. PRESSURE AND QUANTITY HELD STEADY; AND THE FE RAN THE ABNORMAL CHKLIST. WHILE HE WAS FINISHING; THE OTHER 'B' SYS LOW PRESSURE LIGHT CAME ON AND 'B' SYS PRESSURE FLUCTUATED. QUANTITY HELD STEADY AND SYS 'A' INDICATIONS WERE NORMAL. WE CONSULTED WITH THE FLT MANUAL AND MAINT CTL AND CONCLUDED THAT THERE WAS NO CORRECTIVE ACTION THAT WE COULD TAKE. WE CONSULTED WITH DISPATCH AND INFORMED THEM THAT WE DIDN'T WANT TO GO TO LGA DUE TO THE ABNORMAL FLAP SETTING AND ASSOCIATED HIGHER APCH SPD. WE OPTED TO PROCEED TO EWR; WHICH HAD LONGER RWYS AND BETTER SUPPORT FACILITIES. IN MAKING THIS DECISION; WE OVERFLEW CLE; WHICH WAS PROBABLY THE CLOSEST SUITABLE ARPT AT WHICH WE COULD HAVE LANDED AFTER DETERMINING THE NATURE OF THE PROBLEM AS BEST WE COULD. BY THE TIME WE; AS A CREW; DISCUSSED THE IMPLICATIONS OF AN 'A' SYS FAILURE; HOWEVER REMOTE; WE WERE ALMOST AS CLOSE TO EWR AS CLE AND AFTER CHKING WX FOUND THAT EWR WAS MORE FAVORABLE (PARTICULARLY WITH XWINDS; WHICH WERE A FACTOR IN THE APCH DUE TO PARTIAL RUDDER LOSS). WE DECLARED AN EMER AT THAT TIME AND PROCEEDED TO AN UNEVENTFUL LNDG AT EWR. IT TURNED OUT THAT THERE WAS A LEAK IN SYS 'B.' THE QUANTITY WAS DEPLETED AND THERE MAY HAVE BEEN MORE QUANTITY LOSS IN SYS 'A' THAN IS THEORETICALLY POSSIBLE. THE 'B' SYS QUANTITY GAUGE WAS INOP AND THERE WAS SOMETHING UNUSUAL GOING ON WITH 'A.' LESSONS: 1. WE HAD CONFLICTING INFO WHICH INITIALLY CAUSED ME TO NOT TREAT THE PROBLEM WITH THE SERIOUSNESS THAT IT MERITED. 2. WE OVERFLEW A SUITABLE FIELD; WHICH I WON'T DO AGAIN. THERE WERE A LOT OF FACTORS THAT WENT INTO THAT DECISION. SOME OF THOSE; SUCH AS BETTER SUPPORT FACILITIES FOR BOTH CUSTOMERS AND MAINT; WOULD REALLY BE IRRELEVANT SHOULD 'A' SYS HAVE FAILED; TOO. 3. DECISION MAKING IN A COLLECTIVE ENVIRONMENT AND COORD BTWN US (AND THE CABIN TEAM) WENT EXTREMELY WELL. THUMBS UP FOR COCKPIT CREW COORD CLASSES!