AN ATP RATED CFI ON TRAINING FLT AT FWS FAILED TO GET 3 GREEN LIGHT GEAR SAFE INDICATION ON SELECTION OF LNDG GEAR RESULTING IN THE R MAIN GEAR COLLAPSE ON AFTER TOUCHDOWN.

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I WAS TRAINING WITH THE OWNER OF THE ACFT IN PREPARATION FOR HIS CHK RIDE. WE HAD BEEN PERFORMING AIRBORNE MANEUVERS IN PREPARATION FOR HIS CHKRIDE. THE LNDG GEAR WORKED FLAWLESSLY WHEN OPERATED DURING THESE MANEUVERS. WHEN THE MANEUVERS WERE COMPLETED; WE ENTERED THE TFC PATTERN FOR RWY 17R AT FWS. I DIRECTED THE STUDENT/OWNER OF THE ACFT TO EXECUTE A MAX PERFORMANCE LNDG TO A FULL STOP. THE GEAR WORKED FLAWLESSLY FOR THIS MANEUVER. WE TAXIED BACK AND COMPLETED A RUNUP. WE TOOK OFF AND I PULLED BACK THE R THROTTLE TO SIMULATE AN ENG FAILURE AFTER TKOF. MY STUDENT FLEW AROUND THE TFC PATTERN TO SET UP FOR A LNDG. WHEN THE GEAR WAS DEPLOYED; WE DID NOT GET A GREEN LIGHT. AT THIS POINT; I TOOK OVER CTL OF THE AIRPLANE AND RESTORED THE THROTTLES FULL FORWARD AND EXECUTED A GAR. I CYCLED THE GEAR UP. THE ORANGE LIGHT WORKED. I ATTEMPTED TO LOWER THE GEAR A SECOND TIME AND COULD FEEL IT GOING DOWN INTO PLACE. HOWEVER; WE DID NOT GET A GREEN LIGHT. WE FLEW AROUND AND CHKED THE LIGHT BULBS. THEY WERE OK. THE LNDG GEAR CIRCUIT BREAKER HAD NOT TRIPPED. WE FLEW BY THE TERMINAL TWICE AND VERIFIED THE GEAR DOWN AND LOCKED BY GND PERSONNEL. AT THIS POINT I ELECTED TO ATTEMPT A LNDG. I 'GREASED ON' THE LNDG WITH A L XWIND. THE LNDG WAS SMOOTH. THE ROLLOUT WAS SMOOTH AND WENT WELL UNTIL 40-50 MPH; WHEN THE R MAIN GEAR COLLAPSED. THERE WAS NOT ANY MAJOR STRUCTURAL DAMAGE. ONLY THE R GEAR DOOR AND AN 8 INCH SECTION OF THE LOWER AFT R MAIN FUEL TANK FAIRING WERE DAMAGED ON THE ACFT AIRFRAME. THE PROPS WERE Q-TIPPED BY 3 INCHES BUT WE PULLED THE MIXTURE JUST AS THE GEAR COLLAPSED. I THINK THE ENG IS OK; BUT IT WILL NEED A MICROMETER. THE FLAPS WERE NOT DAMAGED EVEN THOUGH THEY WERE AT 35 DEGS. THE COLLAPSE OF THE R MAIN GEAR OCCURRED APPROX 200-300 YARDS AFTER TOUCHDOWN. THE NOSE GEAR AND THE L MAIN GEAR WERE FINE. BOTH OF THESE LNDG GEAR WERE FULLY DOWN AND LOCKED. IT IS MY UNDERSTANDING THAT WHEN THE MAIN LNDG GEAR ARE WITHIN 17 DEGS OF VERT 'STRAIGHT DOWN' THEY ARE SUPPOSED TO GO INTO OVERCTR POS; EVEN IF ELECTRICAL PWR IS REMOVED. HOWEVER; THE CIRCUIT BREAKER WAS OK. THE ONLY CONCLUSION THAT I CAN DRAW IS THAT THERE MUST HAVE BEEN A MECHANICAL FAILURE OF SOME SORT ON THE R MAIN GEAR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES ON CALLBACK THAT THE FAA HAD SENT A LETTER TO THE MECH RESPONSIBLE FOR THE MAINT ON THIS C310 AND THAT HE THOUGHT THAT IMPROPER MAINT HAD BEEN PERFORMED ON THE ACFT. RPTR FURTHER STATES THAT HE DID NOT COMPLETE THE ABNORMAL OR EMER GEAR EXTEND CHKLIST.