Narrative:

It was day 2 of 4 and the second leg of 3. We swapped aircraft. The previous inbound crew had written the aircraft up for a 'feel dif' light. Maintenance was performed on the aircraft draining the elevator feel pitots and the replacement of a check valve in the hydraulic system. The aircraft was returned to service and we departed. About 1 hour into the flight; the 'feel dif' light illuminated. The captain/pilot monitoring pulled out the QRH and we ran the checklist. After running the checklist we observed that the 'a' system hydraulic quantity was indicating 66% and the 'B' 94%. The hydraulic pressures indicated normal but the quantities were dropping about 1% every 5 mins. I was the first officer and PF had continued to handle the aircraft and radios while the captain/pilot monitoring contacted dispatch and maintenance control. A joint decision was made between all parties that the best course of action was to divert to ZZZ. We landed at ZZZ at 700 pounds overweight without incident. After the captain completed all the write-ups; we handed the aircraft over to maintenance. We walked across the hall to another aircraft and continued our trip.

Related reports:

Google
 

Original NASA ASRS Text

Title: B737 ENROUTE EXPERIENCED A HYD FLUID QUANTITY DECREASE; DECLARED AN EMERGENCY AND DIVERTED FOR AN UNEVENTFUL OVERWEIGHT LANDING.

Narrative: IT WAS DAY 2 OF 4 AND THE SECOND LEG OF 3. WE SWAPPED ACFT. THE PREVIOUS INBOUND CREW HAD WRITTEN THE ACFT UP FOR A 'FEEL DIF' LIGHT. MAINT WAS PERFORMED ON THE ACFT DRAINING THE ELEVATOR FEEL PITOTS AND THE REPLACEMENT OF A CHK VALVE IN THE HYD SYS. THE ACFT WAS RETURNED TO SVC AND WE DEPARTED. ABOUT 1 HR INTO THE FLT; THE 'FEEL DIF' LIGHT ILLUMINATED. THE CAPT/PLT MONITORING PULLED OUT THE QRH AND WE RAN THE CHKLIST. AFTER RUNNING THE CHKLIST WE OBSERVED THAT THE 'A' SYS HYD QUANTITY WAS INDICATING 66% AND THE 'B' 94%. THE HYD PRESSURES INDICATED NORMAL BUT THE QUANTITIES WERE DROPPING ABOUT 1% EVERY 5 MINS. I WAS THE FO AND PF HAD CONTINUED TO HANDLE THE ACFT AND RADIOS WHILE THE CAPT/PLT MONITORING CONTACTED DISPATCH AND MAINT CTL. A JOINT DECISION WAS MADE BTWN ALL PARTIES THAT THE BEST COURSE OF ACTION WAS TO DIVERT TO ZZZ. WE LANDED AT ZZZ AT 700 LBS OVERWT WITHOUT INCIDENT. AFTER THE CAPT COMPLETED ALL THE WRITE-UPS; WE HANDED THE ACFT OVER TO MAINT. WE WALKED ACROSS THE HALL TO ANOTHER ACFT AND CONTINUED OUR TRIP.

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.