NOSE GEAR SEPARATED FROM ACFT DURING LNDG.

Narrative

WE DEPARTED ABOUT XX30 AM FOR AN ACFT FAMILIARIZATION FLT IN A C310C. AFTER COMPLETING SOME AIRWORK; STALLS; STEEP TURNS; AND MCA; WE PROCEEDED TO A LCL UNCTLED ARPT TO PRACTICE TAKING OFF AND LNDG. ON OUR SECOND LNDG; AFTER THE MAIN GEAR HIT THE GND; THE NOSE OF THE ACFT SETTLED FIRMLY TO THE SURFACE OF THE RWY. MY EXAMINATION OF THE ACFT AFTER EXITING THE ACFT REVEALED TO ME THAT THE NOSE GEAR HAD COMPLETELY COME OFF THE AIRPLANE. IN A CONVERSATION WITH THE ACFT OWNER AFTERWARDS; HE NOTED THAT A PAX EARLIER IN THE WK MENTIONED HE HAD EXPERIENCED THE SCARIEST LNDG OF HIS LIFE EARLIER IN THE WK. ALTHOUGH IT IS IMPOSSIBLE AT THIS POINT TO DETERMINE THE EXACT CONDITION OF THE ACFT PRIOR TO THIS FLT; IN TAKING A CLOSE LOOK AT THE ACFT WITH AN A&P THERE IS EVIDENCE THAT THE ACFT MAY HAVE BEEN INVOLVED IN A PREVIOUS LNDG INCIDENT. ALTHOUGH THE PREFLT WAS CONDUCTED ACCORDING TO THE PLTS OPERATING HANDBOOK; LOOKING BACK AT THE CIRCUMSTANCES; THAT WAS NOT ENOUGH. AS A PLT; IT WOULD BE IMPOSSIBLE TO DETERMINE EVERY POSSIBLE PROB OR MALFUNCTION THAT MAY OCCUR IN FLT; BUT IT IS ESSENTIAL THAT WE INSPECT THE ACFT PRIOR TO FLT LOOKING FOR PROBS THAT MIGHT NOT BE EXTREMELY OBVIOUS. ALSO; AN INSPECTION OF THE ACFT AFTER IT WAS RPTED TO HAVE BEEN INVOLVED IN A SCARY SIT MAY HAVE PREVENTED THIS INCIDENT FROM EVER OCCURRING.