SEAPLANE GEAR COLLAPSE ON TURN OFF RWY.

Narrative

DURING ENTRY TO TFC PATTERN THE PIC; FLYING FROM L SEAT; LOWERED LNDG GEAR. I WAS FLYING THE TFC PATTERN FROM THE R SEAT. WHEN THE GEAR WAS DOWN; WE BOTH VISUALLY CHKED THAT THE GEAR WAS DOWN (THE GEAR IS VISIBLE FROM COCKPIT). THE GEAR POS LIGHT WENT FROM RED (UP) TO GREEN (DOWN). DURING SHORT FINAL; THE PIC TOOK CTL OF ACFT. AT THIS TIME THE FINAL GEAR CHK WAS MADE BY BOTH PLTS. AT THIS TIME WE BOTH HAD EVERY INDICATION THAT THE GEAR WAS DOWN AND LOCKED. AFTER TOUCHDOWN; AS WE WERE TURNING ON THE TAXIWAY; THE MAIN GEAR COLLAPSED. THE ACFT SKIDDED TO A HALT. THE PRELIMINARY INSPECTION SHOWED ALMOST NO DAMAGE TO THE ACFT. THE PLANE JUST SKIDDED ON ITS KEEL (THE ENG AND PROP ARE LOCATED ON TOP OF THE WING AND RECEIVED NO DAMAGE). AT THIS TIME; THE LNDG GEAR HAS NOT BEEN INSPECTED. MAINT PERSONNEL FEEL THE FOLLOWING IS THE CAUSE: WHEN THE GEAR WAS LOWERED; THE LOCKING PIN DID NOT ENGAGE. EVEN WITHOUT THE LOCKING PIN IN PLACE; THE GEAR VISUALLY APPEARED DOWN AND LOCKED. THE GREEN GEAR LIGHT CAME ON WITHOUT THE GEAR BEING LOCKED. THE SMOOTH TOUCHDOWN AND ROLL OUT DIDN'T STRESS THE GEAR ENOUGH TO CAUSE ITS RETRACTION. DURING TAXIWAY TURN OFF; THE BRAKES WERE APPLIED AND THE GEAR ROTATED BACKWARDS AND THE ACFT SLID ON ITS KEEL.