SMT HAD L MAIN GEAR UNSAFE LIGHT. L GEAR COLLAPSED DURING LNDG ROLL.

Narrative

THE LNDG GEAR WAS PLACED IN THE DOWN POS WITH ONLY THE NOSE GEAR AND THE R MAIN GEAR INDICATING DOWN AND LOCKED. THE GEAR CYCLED UP AND DOWN; SAME RESULTS WERE OBSERVED. THE PROPER CHKLIST OF MANUAL GEAR EXTENSION WAS FOLLOWED; THE SAME CONDITIONS STILL EXISTED (L MAIN WHEEL INDICATION NOT DOWN AND LOCKED). AT THIS TIME I REQUESTED THAT ONE OF MY PAX WHO IS PLT RATED TO PERFORM A VISUAL INSPECTION FROM THE AFT REAR VIEW WINDOW WHICH ALLOWS A GOOD VISUAL VIEW TO THE MAIN LNDG GEAR AND COMPARE IT TO THE R MAIN GEAR. THE PLT IS FAMILIAR WITH THE ACFT AND HAS STATED THAT BOTH MAIN GEARS COMPARE EQUALLY; DOWN AND LOCKED. AT THIS TIME I ELECTED TO PERFORM A FLY-BY BY THE TWR TO OBTAIN A VISUAL INSPECTION FROM TWR AS WELL. THE FLY-BY WAS PERFORMED AND TWR INDICATED THAT THE L MAIN GEAR APPEARS TO BE DOWN AND LOCKED. ALTHOUGH THAT WAS A VALID OBSERVATION; BUT AS THE PIC AND FOR THE SAFETY OF PAX; THAT WAS NOT SATISFACTORY TO COMPLY WITH ATC CLRNC. GEAR APPEARS TO BE DOWN AND LOCKED; CLRED TO REENTER R DOWNWIND RWY 9R CLRED TO LAND. MY RESPONSE BEFORE LNDG WHILE ON R BASE RWY 9R REQUEST A LOW APCH WITH A SE DEP OVER THE WATER TO PERFORM G-LOAD MANEUVERS TO FORCE THE L MAIN GEAR DOWN. THE MANEUVERS WERE PERFORMED WITH THE SAME INDICATION. AT THIS TIME I REPEATED THE STEPS FOR MANUAL GEAR EXTENSION AFTER EVERYTHING ELSE KEPT THE SAME INDICATION. AFTER THE STEPS WERE REPEATED I WAS NO LONGER GETTING WARNING HORN INDICATION WHEN THE THROTTLE WAS RETARDED INDICATING THE GEAR IS DOWN AND LOCKED; THOUGH THE L MAIN GEAR LIGHT WAS OUT. WITH THE WARNING HORN INDICATING THAT GEAR IS DOWN AND LOCKED AND ALL OTHER RESOURCES FROM VISUAL INSPECTION TO FLY-BY AND TWR OBSERVATION ALL INDICATED THAT THE GEAR WAS DOWN AND LOCKED AND VIRTUALLY WAS A MICROSWITCH FAILURE AND IN FACT THE GEAR IS DOWN AND LOCKED. I DID NOT DECLARE AN EMER BASED ON THE RESOURCES. I WAS CLRED TO LAND. A SOFT LNDG WAS PERFORMED ON THE R MAIN GEAR; FOLLOWED BY A SMOOTH TOUCHDOWN ON THE L MAIN. ACFT ROLLED FOR APPROX 700-1000 FT AND A CRACK WAS HEARD BY A WITNESS ON THE GND. THEREAFTER THE ACFT STILL ROLLED FOR ADDITIONAL 50- 100 FT AND COLLAPSED ON THE L SIDE (LIGHT BRAKING WAS APPLIED PRIOR TO THE COLLAPSE). SKIDDED TO THE L SIDE OF THE RWY AND EVENTUALLY TO THE GRASS SIDE OFF THE RWY.