A FOKKER 100 AFTER TKOF RETURNED TO THE FIELD DUE TO NUMEROUS AIR SENSING MULTIPLE FUNCTIONAL DISPLAY UNIT FAULTS AND THE NECESSITY TO USE OVERRIDE TO RAISE THE LNDG GEAR CAUSED BY AN INCORRECT ADJUSTMENT OF THE L MAIN GEAR GND SENSOR.

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ON FEB/XX/98; I WAS ASSIGNED TO CHANGE THE L HAND MAIN LNDG GEAR SHIMMY DAMPER. ON REMOVAL OF THE DAMPER; IT WAS DISCOVERED THAT THE LOWER TORQUE LINK WAS FROZEN (WOULD NOT MOVE WITHOUT EXCESSIVE FORCE). SOME TIME WAS SPENT ATTEMPTING TO LOOSEN THE LINK BY LUBING; EXERCISING; ETC; TO NO AVAIL. THE REST OF MY SHIFT WAS SPENT IN REMOVAL OF THE LOWER TORQUE LINK. NEXT TWO SHIFTS WERE USED BY OUR MACHINISTS TO REPLACE BOTH THE UPPER AND LOWER TORQUE LINKS; LINK BUSHINGS AND LINK PINS. WHEN I RETURNED TO WORK ON FEB/XY/98; I WAS ASSIGNED WITH 2 OTHER MECHS TO FINISH THE REASSEMBLY OF THE L HAND MAIN LNDG GEAR STRUT (INSTALL BRACKETRY; HYD LINES; WIRING; BRAKES; WHEELS; TORQUE LINK DAMPER; ETC). DURING REASSEMBLY; A CO-WORKER ACCIDENTALLY BROKE THE INBOARD AIR/GND PROX SENSOR WHILE TIGHTENING THE CANNON PLUG ATTACHED TO IT. I ORDERED A NEW ONE AND PROCEEDED TO REPLACE IT IN ACCORDANCE WITH OUR TORQUE LINK REMOVAL/REPLACEMENT JOB CARD AND THE MAINT MANUAL. WE FINISHED THE REST OF THE REASSEMBLY OF THE L HAND MAIN LNDG GEAR; THE LOGBOOK WAS FILLED OUT AND SIGNED OFF AND THE ACFT WAS RETURNED TO SVC ON FEB/XZ/98. ON THE FIRST FLT AFTER RETURNING TO SVC; THE PLTS GOT MESSAGES ON THE MFDU ABOUT AIR SENSING PROBS AND WERE ONLY ABLE TO RETRACT THE LNDG GEAR USING THE OVERRIDE FUNCTION. THEY DECLARED AN EMER AND RETURNED TO FIELD FOR AN UNEVENTFUL LNDG AND RETURNED TO THE GATE. THE ACFT WAS REMOVED FROM SVC; AND DURING A BITE CHK OF THE PROX SENSE SYS; THE REPLACED SENSOR WAS FOUND TO BE OUT OF ADJUSTMENT. ACTUALLY; THE SENSOR IS NON ADJUSTABLE; AND THE SENSOR TARGET WAS OUT OF RIG. THE TARGET WAS ADJUSTED AND THE PROB CORRECTED WITH NO FURTHER DISCREPANCIES. THE JOB CARD; NOR THE MAINT MANUAL MADE REF TO DO A BITE TEST; WHICH WOULD HAVE DISCOVERED THE PROB BEFORE FLT. I AM SUBMITTING A 'REQUEST FOR PUB CHANGE' TO ADD A MORE THOROUGH CHK AND TEST FOR THE ADJUSTMENT OF THE SENSORS ON THE JOB CARD. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT NOTHING IN THE MAINT MANUAL OR THE JOB CARDS FOR THE TORQUE LINK REPLACEMENT AND LNDG GEAR GND SENSOR PROX SENSOR REPLACEMENT REQUIRES A LNDG GEAR RETRACTION TEST. THE RPTR SAID A TEST WOULD HAVE AVOIDED THIS INCIDENT. THE RPTR STATED THE FAA HAS MADE NO CONTACT.