A PIPER PA24 DECLARED AN EMER AND LANDED WITH THE R MAIN LNDG GEAR PARTIALLY EXTENDED INCURRING DAMAGE TO THE R FLAP AND TIP TANK. CAUSED BY A MISADJUSTED R GEAR LIMIT SWITCH.

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MADE A NORMAL DAY VFR APCH TO RWY 29; PERFORMED NORMAL PRE-LNDG (GUMPS) CHKS. ACFT CONDITION WAS NORMAL. TOUCHED DOWN ON THE L (UPWIND) MAIN GEAR; THEN SETTLED ONTO THE R GEAR LEG. IT BECAME APPARENT THAT THE ACFT WAS BEHAVING VERY STRANGELY; SO A GAR WAS INITIATED. ON CLBOUT AND SUBSEQUENT GEAR RETRACTION THE GEAR SYS STOPPED PARTWAY UP AS EVIDENCED BY THE MECHANICAL INDICATOR AND BY THE ABSENCE OF THE NORMAL AMBER UP CONDITION LIGHT. GOT A CALL FROM THE TWR ASKING PERSONS ONBOARD AND FUEL REMAINING -- OBVIOUSLY THEY COULD SEE SOMETHING I COULD NOT. TOLD THE TWR I WAS GOING TO FLY AWAY FROM THE PATTERN TO TROUBLESHOOT. FOUND RETRACTION MOTOR CIRCUIT BREAKER POPPED. MOVED GEAR SWITCH TO DOWN POS AND RESET BREAKER. INBOARD PORTIONS OF GEAR SYS INDICATED FULL DOWN AS SHOWN BY THE MECHANICAL INDICATOR; BUT THIS TIME THERE WAS NO GREEN LIGHT; INDICATING THAT ONE OR MORE OF THE GEAR LEGS WAS NOT FULLY EXTENDED. ACCEPTED THE PREVIOUSLY SUGGESTED LOW APCH FROM THE TWR AT THIS POINT. RPT FROM THE TWR WAS WHAT I EXPECTED: R MAIN GEAR NOT FULLY EXTENDED. CLBED OUT LEAVING THE REMAINING LEGS AS IS AND COMMENCED BURNING OFF FUEL FROM THE PARTIALLY FULL TIP TANKS. CONSIDERED RETURNING THE ACFT TO ITS HOME BASE AS THE FUEL HAD TO BE BURNED OFF ANYWAY; APPROPRIATE REPAIR FACILITIES ARE AVAILABLE; AND THE FIELD WAS FIRE-FIGHTING. EVENTUAL CHK OF WX INDICATED AN ADVERSE WIND CONDITION THERE THOUGH; WHICH WOULD HAVE INVOLVED USING A NARROWER RWY. ALSO; GUST FACTOR AT THE ARPT OF THE ORIGINAL LNDG ATTEMPT HAD DIMINISHED; AND THEY HAVE FIRE-FIGHTING AS WELL; SO FINALLY DECIDED TO LAND THERE. COMPLETED FUEL BURN OFF FROM THE TIP TANKS. COMPLETED CHKLIST FOR LNDG IN EXTREMIS. MADE FULL FLAP VERY SLOW APCH TO RWY 18. WIND WAS STRAIGHT DOWN THE RWY. SET DOWN GENTLY. R FLAP; R TIP TANK; AND TAIL TIE DOWN LUG EVENTUALLY CONTACTED RWY; SPOILING ATTEMPT TO MAKE THE FIRST RWY. SHUT DOWN MAGNETOS; ELECTRICS; AND FUEL. EXITED ACFT. ACFT DID NOT SUSTAIN SUBSTANTIAL DAMAGE. NO INJURIES. ABRADED R LOWER FLAP SKIN AND R TIP TANK. THE FOLLOWING OPINION IS RENDERED PRIOR TO ANY DETAILED EXAMINATION OF THE GEAR SYS. I SUSPECT THAT THERE WAS SOMEHOW TOO LITTLE PRE-LOAD IN THE R GEAR EXTENSION CABLE. INITIAL TOUCHDOWN ON THE L GEAR MAY HAVE MOVED THE GEAR MOTOR XMISSION ENOUGH TO PRODUCE SOME MOTION IN THE R GEAR CABLE ALSO; WHICH MAY HAVE ALLOWED OTHERWISE NORMAL SIDE-LOADING TO INITIATE R GEAR LEG COLLAPSE WITH EVENTUAL EXCESSIVE LOAD ON THE R GEAR EXTENSION ROD. THE GEAR SYS HAD RECENTLY BEEN DISASSEMBLED FOR A SCHEDULED CHK; AND THE ACFT HAD HAD ONLY 3 CYCLES AFTER THIS DISASSEMBLY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THIS AIRPLANE HAS ONLY 1 GREEN LIGHT FOR LNDG GEAR POS DOWN AND LOCKED INDICATIONS. THE RPTR SAID THIS MAKES IT DIFFICULT TO DETERMINE WHAT POS FAILED AND THIS SYS SHOULD HAVE 3 LIGHTS. THE RPTR STATED THE COMPONENT FAILURE WAS ISOLATED TO THE R MAIN GEAR EXTEND LIMIT SWITCH OUT OF ADJUSTMENT. THE RPTR SAID THE ACFT WAS NOT DAMAGED TOO BADLY AS ONLY A LOWER R FLAP SKIN WAS REPLACED AND THE TIP TANK WHILE NOT PUNCTURED REQUIRED WELDING. THE RPTR STATED AN EMER WAS DECLARED.