NOSEWHEEL STEERING CTL VALVE PROB. FIRST SHIFT MECHS PREPARED FOR GEAR SWING AND SET GEAR TEST VALVE TO GND ONLY POS. SHIFT CHANGE; FIRST SHIFT FORGOT TO INCLUDE POS OF TEST VALVE. NEXT SHIFT USED PROC WHICH DIDN'T CALL FOR TEST VALVE IN GND ONLY. CONSEQUENTLY; NOT DISCOVERED UNTIL ACFT RETURNED WITH GEAR PROB.

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HANGAR LINE MAINT; MYSELF AND ANOTHER MECH WERE ASSIGNED TO CHK OUT A NOSE GEAR STEERING PROB ON ACFT. THE PREVIOUS SHIFT HAD CONFIGURED THE ACFT ON JACKS WITH A HYD MULE CONNECTED TO #1 HYD SYS. THE PREVIOUS SHIFT STATED ON A MAINT TURNOVER FORM THEY HAD CHANGED A STEERING CTL VALVE AND RIGGED THE NOSE GEAR STEERING CTL AND FEEDBACK CABLES; BUT THEY COULD NOT ACHIEVE THE MAINT MANUAL LIMITS FOR NOSE GEAR CTRING. WHEN WE STARTED WE RECHKED ALL NOSE GEAR CABLE RIGGING AND STEERING CTL VALVE INSTALLATION AND RIGGING PER FOKKER MAINT MANUAL. ALL SYS RELATED TO STEERING FELL WITHIN MAINT MANUAL LIMITS EXCEPT CTRING AND WE NOTICED THE STEERING CTL VALVE LEAKING INTERNALLY. WE ORDERED A NEW VALVE. ON JAN/YY/96 THE MECHS STARTED THE NEW VALVE INSTALLATION. AT XA00 HRS; MYSELF AND THE SAME MECH FROM THE PREVIOUS DAY FINISHED THE INSTALLATION PER THE FOKKER MAINT MANUAL. WE STILL COULDN'T ACHIEVE MAINT MANUAL LIMITS PER MAINT MANUAL FOR NOSE GEAR CTRING. WE WERE STILL 1 DEG L AND 1 DEG R OF MAX LIMITS. FOKKER APPROVED DEV FROM MAINT MANUAL LIMITS. WE THEN HAD THE SYS INSPECTED AND PERFORMED SEVERAL GEAR SWINGS WITH THE HYD MULE CONNECTED. NO FAULTS WERE NOTED AND WE LOWERED THE ACFT OFF JACKS; DISCONNECTED THE HYD MULE AND SVCED THE HYD SYS. DURING THIS MAINT PROC FROM JAN/YY/96 TO JAN/YY/96 SOMEONE TURNED THE LNDG GEAR GND MAINT VALVE IN THE R WHEEL WELL; FROM THE NORMAL MODE TO THE GND MODE. THE MOVEMENT OF THIS VALVE WAS NEVER DOCUMENTED. FOKKER MAINT MANUAL TELLS YOU ONLY TO MOVE THIS VALVE WHEN PERFORMING LNDG GEAR SWINGS WITH ACFT HYD ELECTRIC PUMPS. THIS VALVE DOESN'T HAVE TO BE MOVED WHEN USING A HYD MULE. SINCE NOTHING WAS DOCUMENTED IN A MAINT TURNOVER FORM ABOUT THIS VALVE BEING MOVED TO THE MAINT POS; THEN NEITHER MYSELF NOR THE MECH WORKING WITH ME HAD ANY REASON TO BELIEVE THAT THE GND MAINT VALVE WAS IN THE GND POS; THEREFORE THE MAINT PROC WAS INADVERTENTLY CLRED AND THEN THE ACFT WAS RELEASED FOR SVC. ON FEB/XX/96 THE ACFT RETURNED TO FIELD AFTER TKOF. DURING GEAR RETRACTION THE CREW HAD A LNDG GEAR ALERT AND MESSAGE. UPON RETURNING TO THE FIELD; LINE MAINT REPOSITIONED THE VALVE TO THE NORMAL POS AND THE ACFT RETURNED TO SVC. THIS IS A RECURRENCE WITH THE F100 ACFT. FOKKER SHOULD HAVE ANNUNCIATOR LIGHT OR SOME OTHER VISUAL MEANS FOR CREWS AND MECHS TO SEE IF THIS VALVE HAS BEEN TURNED. THE ONLY WAY TO SEE IT IS TO CRAWL INTO THE WHEEL WELL. SUPPLEMENTAL INFO FROM ACN 327291: CORRECTIVE ACTION SUGGESTIONS: 1) INSTALLATION OF A SWITCH THAT IS MADE BY THE HANDLE AND TURNS ON AN INDICATION LIGHT IN COCKPIT. 2) USE OF AN ELECTRIC HYDRO PUMP THAT SUPPLIES ENOUGH VOLUME TO ELIMINATE THE TEST VALVE. 3) RELOCATING THE TEST VALVE TO A MORE ACCESSIBLE LOCATION TO BE FLAGGED.