A SLOW B717 HYD LEAK INITIALLY INDICATED A LOW QTY; THEN A NORMAL QTY. AFTER LNDG GEAR EXTENSION; QTY CONTINUOUSLY DECREASED TO .6 UPON GATE ARR.

Narrative

NORMAL TKOF AND CLB TO FL340. IN CRUISE ABOUT 45 MINS INTO FLT WE GOT A 'HYD R QUANTITY LOW' INDICATION. WE PULLED OUT THE QRH AND RAN THE CHKLIST. SHORTLY AFTER RUNNING THE CHKLIST WE NOTICED THE HYD QUANTITY INCREASING FROM THE LOW OF 3.8 UP TO 8.5. WE CALLED MAINT ON VHF TOLD THEM ABOUT OUR INDICATIONS. THEY SAID IT MIGHT BE AN INDICATION PROB SINCE THE QUANTITY INCREASED. I TOLD THEM THAT I WAS ON THE ARR INTO ZZZ AND THAT I WOULD TRY TURNING THE PUMPS ON AND LOWERING THE GEAR WHEN I WAS CLOSER. ABOUT THIS TIME ATC TOLD ME TO EXPECT HOLDING. WE WERE DSNDING THROUGH 13000 FT. AT THIS POINT WE DECLARED AN EMER. I DID NOT WANT TO BURN MORE FUEL NOT KNOWING MY HYD STATUS. I WANTED TO TRY EXTENDING MY GEAR AND SEE WHAT WE HAD. ATC VECTORED US IN. 25 MI OUT WE EXTENDED OUR GEAR. GEAR AND FLAPS EXTENDED NORMALLY BUT HYD QUANTITY BEGAN DROPPING RAPIDLY. WE EXTENDED FLAPS 40 DEGS. WE CALLED OUT EMER EQUIP AS A PRECAUTION. WE TOLD ATC THAT WE HAD NORMAL GEAR AND LNDG CONFIGN. LNDG WAS UNEVENTFUL WITH NORMAL NOSE GEAR STEERING. WE HAD NORMAL HYD PRESSURE DURING THE WHOLE FLT. I TURNED OFF THE R ENG HYD PUMP AS SOON AS WE CLRED THE RWY. QUANTITY HAD CONTINUED TO DROP TO ABOUT .6 AS WE PARKED. MAINT TOLD US THERE WAS A HYD PUMP LEAK ON THE R SIDE. I AM SPECULATING; BUT I BELIEVE AIR MAY HAVE GOTTEN INTO THE SYS CAUSING FALSE QUANTITY READINGS. FLUID WAS APPARENTLY IN THE COWLING TRAPPED AND NOT FOUND UNTIL MAINT INSPECTED THE AIRPLANE FURTHER. WE DID NOT SEE ANY FLUID ON INITIAL POSTFLT INSPECTION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER STATED THAT DURING HIS AIRBORNE CONVERSATION WITH HIS ACR MAINTENANCE; A SUGGESTION WAS MADE THAT AIR MAY HAVE BEEN INTRODUCED INTO THE SYSTEM. DURING TROUBLESHOOTING AFTER LNDG; IN FACT LOW HYD QTY WAS OBSERVED BUT THE LEAK WAS VERY DIFFICULT TO DETECT BECAUSE IT WAS SO SMALL. EVENTUALLY; THE LEAK WAS FOUND; BUT THE CAUSE OF THE HYD QTY INCREASE COULD NOT BE DETERMINED.