HARD LNDG; NOSE GEAR COLLAPSES ON LNDG PROC.

Narrative

I WAS L SEAT INSTRUCTOR. STUDENT WAS FLYING THE PLANE FROM THE R SEAT. STUDENT WAS PERFORMING A SHORT FIELD; 50 FT OBSTACLE LNDG. I HAD JUST DEMONSTRATED ONE ON THE TKOF AND LNDG PRIOR. HE SET UP A STABILIZED PWR-ON APCH TO CLR THE 50 FT OBSTACLE. AS HE FLEW I VERBALIZED THE NEXT STEP. I REITERATED TO HIM THAT IN THE TRANSITION FROM APCH TO FLARE HE WOULD NEED A LITTLE BIT MORE PWR THAN NORMAL IN ORDER TO REDUCE THE SINK RATE TO MAKE A SAFE LNDG. AS THE INSTRUCTOR; MY HAND WAS ON THE PWR QUADRANT. HIS HAND ON THE THROTTLES; MY HAND BELOW HIS ON THE THROTTLE SHAFTS. AS HE CLRED THE OBSTACLE HE CHOPPED THE PWR INSTEAD OF ADDING PWR. I ADDED PWR TO REDUCE THE SINK RATE. HIS HAND RESISTED A LITTLE AND PREVENTED ME FROM GETTING ALL THE PWR I WANTED BUT I WAS ABLE TO ARREST THE SINK RATE AND MAKE A FIRM LNDG. THE MAINS TOUCHED DOWN; THEN I CHOPPED THE PWR; THEN THE NOSEWHEEL TOUCHED. THE NOSEWHEEL CONTINUED ON THROUGH AS IT COLLAPSED. THE LNDG WAS NOT HARD OR EXCESSIVE. IT WAS NOT; IN MY OPINION; FIRM ENOUGH TO CAUSE THE COLLAPSE. I SUSPECT MECHANICAL FAILURE. THE NOSE GEAR HAD HAD SOME WORK DONE ON IT IN JAN/93 (ONLY A FEW TKOFS AND LNDGS AGO). ALSO; THESE SMA'S HAVE A NOSE GEAR COLLAPSING PROB. I DO NOT KNOW THE CAUSE AT THIS TIME.