PLT OF C172RG BELIEVES NOSE GEAR COLLAPSE DURING PRACTICE SOFT FIELD TKOF MAY HAVE BEEN SELF INDUCED BY KNEE STRIKING GEAR LEVER.

Narrative

TRAINING IN THE RG; ABOUT 6 TKOFS AND LNDGS HAD BEEN COMPLETED WITHOUT INCIDENCE. PRIOR TO ANOTHER TKOF A PRETKOF CHKLIST WAS COMPLETED AND EVERYTHING WAS IN ORDER. I WAS GOING TO PRACTICE A SOFT FIELD TKOF SO FULL ELEVATOR DEFLECTION WAS APPLIED. I HAD ADVANCED THE THROTTLE FORWARD TRAVELING APPROX 20 KTS WHEN THE NOSE GEAR COLLAPSED. THE PROP STRUCK THE GND AND THE PLANE SLID ABOUT 25 METERS. UPON INSPECTION; I NOTICED THE GEAR LEVER WAS IN THE UP POS; EVEN THOUGH THAT HAD BEEN CHKED. SOMEWHERE BTWN THE PRETKOF CHK AND THE GND ROLL THE LEVER MUST HAVE BEEN PUSHED UP. I'M NOT EXACTLY SURE HOW; BUT MY BEST GUESS IS THAT THE LEVER ITSELF WAS FULLY PUSHED INTO THE LEVER LOCK POS EVEN THOUGH THE LEVER WAS DOWN AND THE GREEN LIGHT SHOWN. MY LEGS ARE FAIRLY LONG AND I'M GUESSING THAT AS I WORKED THE RUDDER MY KNEE PUSHED IT UP; CAUSING THE NOSEWHEEL TO RETRACT. IN THE FUTURE; I MOST CERTAINLY WILL BE CHKING AND RECHKING THE GEAR LEVER TO MAKE SURE THAT IT IS FULLY LOCKED IN ITS PLACE. THE APPEARANCE OF THE LEVER BEING DOWN AND THE GREEN LIGHT IS NOT ENOUGH. ANOTHER STEP I WILL BE TAKING IS TO SLIDE MY SEAT BACK AN EXTRA NOTCH TO MAKE SURE MY KNEE CANNOT BE THAT CLOSE TO THE CTL PANEL.