A CESSNA 414 ON TOUCHDOWN HAD THE R MAIN LNDG GEAR COLLAPSE DUE TO A FAILED OVERCTR LOCKING BOLT.

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I WAS APCHING THE NAPA ARPT FROM THE E. RPTED OVER CORDELIA AND WAS INSTRUCTED TO RPT 'OVER THE WATER TANKS.' STAGE COOLING AND FIRST NOTCH OF FLAPS WERE COMPLETE AND LNDG GEAR WAS EXTENDED PRIOR TO THE WATER TANKS AND INDICATED 3 GREEN LIGHTS. I RPTED OVER THE WATER TANKS AND WAS CLRED TO LAND ON RWY 24. APCH WAS NORMAL. AS THE ACFT SETTLED ONTO THE RWY; THE R SIDE FELT AS IF IT WERE SINKING LOWER THAN USUAL. I GLANCED AT THE GEAR INDICATORS AND SAW A RED 'UNSAFE' LIGHT. I APPLIED FLT CTL CORRECTIONS TO RAISE THE R WING AND ADDED PWR TO GO AROUND. I ADVISED THE TWR OF THE GAR AND SAID THAT SOMETHING FELT UNUSUAL WITH THE R MAIN GEAR (A PLT IN THE RUNUP AREA OF 24 CONFIRMED THAT THE GEAR APPEARED TO HAVE BEEN COLLAPSING). I PERFORMED A L XWIND DEP TO THE S AND CLBED TO DIAGNOSE THE PROB. I ALERTED OUR MAINT CREW VIA UNICOM. WHILE WAITING FOR THEM TO GET A RADIO UP AND FUNCTIONING; I ATTEMPTED SEVERAL GEAR EXTENSIONS AT VARIOUS AIRSPDS WITH AND WITHOUT SLIPS; AS WELL AS VARYING FLT ATTITUDES ALL WITHOUT SUCCESSFULLY LOCKING THAT LAST MAIN. I ATTEMPTED MANUAL GEAR EXTENSIONS AGAIN WITHOUT SUCCESS. MAINT UNDERSTOOD MY SIT AND WE WORKED TOGETHER TO TRY TO SOLVE THE PROB. THEY WERE NOW IN POS TO OBSERVE THE GEAR FROM THE GND VIA LOW PASS. WINDS WERE LIGHT AND VARIABLE AND I TALKED WITH THE TWR AND DECIDED RWY 24 WOULD CAUSE THE LEAST INCONVENIENCE TO OTHER PLTS AND KEEP THE ARPT OPEN AND OPERATING. I FLEW L TFC AND PERFORMED A LOW PASS ALLOWING OUR MAINT CREW TO GET ITS BEST LOOK AT THE R GEAR. AS FAR AS WE COULD DETERMINE; THE GEAR LOOKED NORMAL. I MADE L TFC; DECIDING TO KEEP THE FLAPS UP TO MINIMIZE ANY AIRFRAME DAMAGE. SINCE THE MAIN GEAR EXTENDS FROM THE AIRFRAME CTRLINE TOWARDS THE WINGTIPS; I ALSO DECIDED A SLIGHT CRAB MAY PROVIDE ENOUGH OUTWARD ENERGY TO LOCK THAT LAST GEAR. PATTERN WAS NORMAL. AS I CROSSED THE RWY NUMBERS; I PULLED THE MIXTURES TO IDLE CUTOFF AND TURNED OFF THE 2 GANG BARS THAT SHUT DOWN THE IGNITION AND ELECTRICAL SYS. I TOUCHED DOWN THE L MAIN FIRST HOPING THAT MAY NUDGE THE R MAIN TO LOCK. NO LUCK. I THEN TOUCHED THE R MAIN HOPING THE YAW MAY PROVIDE ENOUGH FORCE TO LOCK THAT GEAR. NO LUCK. I COULD FEEL THE R SIDE SINKING AGAIN AND HELD IT UP AS LONG AS THE AIRSPD AND GRAVITY WOULD ALLOW. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE LNDG GEAR IS ACTIVATED BY A SINGLE ELECTRIC MOTOR; DRIVING PUSH RODS CONNECTED TO EACH LNDG GEAR. THE RPTR SAID THE R LNDG GEAR ROD END FITTING BOLT WAS FOUND SHEARED; WHICH CAUSED THE FAILURE.