C172RG STUDENT PLT AND INSTRUCTOR PLT HAD THE LNDG GEAR COLLAPSE ON LNDG.

Narrative

I WAS FLYING R SEAT; TRAINING FOR CFI-A CHK RIDE WITH MY INSTRUCTOR. INCIDENT OCCURRED ON 7TH TOUCH-AND-GO. I PERFORMED GUMPS CHKLIST ABEAM THE NUMBERS. WE WERE DOING A PWR-OFF 180 DEG ACCURACY LNDG -- GEAR DOWN; GREEN LIGHT; MIXTURE; PROP; THROTTLE; ETC. CARB HEAT ON. A NORMAL BASE; FINAL; AND ON FLARE; GEAR COLLAPSED OR HAD NOT COME DOWN; SKIDDED TO A STOP. GEARWHEELS WERE SMASHED UNDERNEATH ACFT; BUT HAD BEEN PUT DOWN. CONTRIBUTING FACTORS: THIS ACFT HAD PREVIOUSLY HAD A GEAR MALFUNCTION IN THE PREVIOUS 7 MONTHS (A GEAR INCIDENT). HOWEVER; I SHOULD HAVE VISUALLY IDENTED THAT THE GEAR WAS DOWN AND I WAS TOO FOCUSED ON THE POINT ON THE RWY WHERE I WAS TO LAND WITHOUT PWR. I RELIED ON INSTRUCTOR TO MONITOR THE GEAR DOWN OUTSIDE THE WINDOW INSTEAD OF DOING IT MYSELF. HAD I BEEN ONLY PLT ON ACFT; I WOULD NOT HAVE LANDED WITHOUT CHKING GEAR VISUALLY. SUPPLEMENTAL INFO FROM ACN 636186: BOTH MY STUDENT AND I SAW AND CONFIRMED THE GREEN LIGHT INDICATING THE GEAR TO BE DOWN AND LOCKED. WE DO NOT KNOW IF THE GEAR SAFE INDICATION WAS FALSE AND THE GEAR NEVER LOCKED INTO PLACE; OR IF THE GEAR HAD ACTUALLY LOCKED AND COLLAPSED ALL THE SAME. THE ACFT SUFFERED DAMAGE TO THE BELLY SKIN; ALL BELLY ANTENNAS AND THE PROP DUE TO IT STRIKING THE GND. I BELIEVE THIS ACCIDENT OCCURRED BECAUSE OF AN UNRELIABLE GEAR DOWN INDICATION (GREEN LIGHT). AT THIS TIME I DO NOT KNOW HOW THIS COULD OCCUR AND DO NOT HAVE ANY SUGGESTIONS ON HOW THIS KIND OF INCIDENT COULD BE AVERTED.