ACFT EQUIP PROB R MAIN GEAR DID NOT LATCH DOWN.

Narrative

I WAS PERFORMING NORMAL PATTERN WORK ON RWY 09R AT BOULDER CITY ARPT. I BROUGHT THE LNDG GEAR DOWN AT MIDFIELD DOWNWIND ABEAM THE NUMBERS RWY 09R. I SIMULATED A FAILED ENG. I PROCEEDED TO MAKE A STANDARD SINGLE ENG PATTERN DOWN TO THE RWY. THE ACFT HAD A SOLID GREEN LIGHT FOR THE GEAR AND A NORMAL FULL STOP LNDG WAS TO BE ACCOMPLISHED. UPON LNDG; THE THROTTLES WERE BROUGHT BACK TO IDLE AND I HAD A NORMAL TOUCHDOWN. AT THAT MOMENT I FELT THE R SIDE OF THE ACFT BEGIN TO FALL TO THE GND. I ADDED PWR AND PULLED BACK ON THE YOKE TO ABORT THE LNDG BEFORE DAMAGE OCCURRED. THE ACFT LIFTED OFF AND ABRUPTLY SETTLED BACK DOWN ON THE GND ABOUT 100 FT FURTHER DOWN THE RWY AND THEN LIFTED OFF AGAIN AND CLBED OUT. IT IS MY BELIEF THAT THE R MAIN COLLAPSED AT THAT TIME AND NO DAMAGE OCCURRED. DURING THE CLB OUT; THE GREEN DOWN LIGHT FROM THE GEAR WAS INTERMITTENT WHICH LED ME TO BELIEVE THE GEAR WAS NOT LATCHED INTO PLACE. I PULLED OUT THE EMER CHKLIST AND CRANKED GEAR DOWN AND THE LIGHT BECAME SOLID GREEN. I THEN MADE A FLYBY FOR THE UNICOM OPERATOR AND THEY SAID THE GEAR WAS LOCKED DOWN. I DID NOT KNOW WHAT WAS WRONG WITH THE GEAR AND DECIDED TO BE SAFE ABOUT IT AND PROCEED BACK TO N LAS VEGAS ARPT. THE ACFT FLEW FINE. I REQUESTED FIRE TRUCKS JUST IN CASE THE GEAR DID NOT HOLD UPON LNDG. I LANDED THE ACFT AND SHUT IT DOWN AND GOT OUT. WE THEN INSPECTED THE AIRPLANE. I BELIEVE I HANDLED THE SIT EXCELLENTLY AND PROFESSIONALLY.