A PA28RT ARROW ON APCH AT 150 FT THE R MAIN GEAR GREEN LIGHT DID NOT ILLUMINATE DUE TO A FAILED R MAIN GEAR POS SENSING MICROSWITCH FAILURE.

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ON MAY/XA/00 I WAS CONDUCTING A BFR IN A PIPER PA28RT-201 ARROW; REGISTRATION #WXWX. I WAS THE FLT INSTRUCTOR AND PIC OF THE ACFT. THE GENTLEMAN I WAS REVIEWING HAPPENED TO BE THE OWNER OF THE ACFT; WHICH MY EMPLOYERS LEASE BACK FOR THEIR FLT SCHOOL. AFTER THE MAJORITY OF THE FLT REVIEW WAS ACCOMPLISHED; WE RETURNED TO THE ARPT TO PRACTICE A FEW TKOFS AND LNDGS. THE FIRST FULL STOP LNDG WAS COMPLETED NORMALLY. ON THE DOWNWIND LEG OF THE NEXT LNDG; THE LNDG GEAR SELECTOR SWITCH WAS PLACED IN THE DOWN POS AND WE WAITED FOR THE 3 GREEN LNDG GEAR INDICATOR LIGHTS TO ILLUMINATE. THE GEAR EXTENSION PROC SEEMED NORMAL ENOUGH; THE PROPER SOUNDS WERE HEARD AS THE GEAR EXTENDED AND I FELT THE USUAL 'BUMP' AS THE GEAR LOCKED INTO PLACE. HOWEVER; THE R MAIN GEAR LIGHT WOULD NOT COME ON. IT FLICKERED BRIEFLY AND THEN WENT OUT. WE DEPARTED THE PATTERN AND CLBED TO A SAFE ALT TO TROUBLESHOOT THE PROB. I INSTRUCTED THE OTHER PLT TO FLY THE ACFT AND WATCH FOR OTHER TFC. I CYCLED THE LNDG GEAR A NUMBER OF TIMES AND VERIFIED THAT THE INDICATOR BULB WAS FUNCTIONING PROPERLY; BUT COULD NOT GET A NORMAL INDICATION FOR THE R MAIN GEAR. I THEN PERFORMED THE EMER MANUAL GEAR EXTENSION PROC AS OUTLINED IN THE POH FOR THE ACFT. AT THIS POINT; I BELIEVED THAT THE LNDG GEAR WAS MOST LIKELY DOWN AND LOCKED AND THAT THE PROB EXISTED WITH THE MICROSWITCH OR WIRING ON THE GEAR ITSELF -- A NOT ALTOGETHER UNHEARD OF OCCURRENCE WITH THAT MODEL OF ACFT. I CONTACTED ANOTHER EMPLOYEE OF THE FLT SCHOOL ON OUR COMPANY FREQ AND ASKED HIM TO CHK THE CONDITION OF MY LNDG GEAR AS I OVERFLEW THE ARPT. THIS PERSON IS A COMMERCIALLY RATED PLT AND CFI CANDIDATE. HE IS VERY FAMILIAR WITH THE ACFT AND I FELT HE COULD AT LEAST GIVE ME A GOOD INDICATION THAT THE GEAR WAS DOWN; IF NOT LOCKED. I OVERFLEW THE N RAMP AREA OF THE ARPT AND MY FRIEND ON THE GND INFORMED ME THAT MY R MAIN GEAR APPEARED TO BE FULLY EXTENDED. I SELECTED AN ALT THAT WOULD PERMIT ME SAFE OBSTACLE CLRNC AND A REASONABLE VIEW OF MY UNDERCARRIAGE TO OBSERVERS ON THE GND; AND ANNOUNCED MY INTENTIONS TO LCL TFC ON THE CTAF. AFTER COMPLETING AN UNEVENTFUL LNDG; IT WAS DETERMINED BY OUR MAINT PERSONNEL THAT A MALFUNCTIONING MICROSWITCH IN THE R MAIN LNDG GEAR WAS RESPONSIBLE FOR THIS SIT.