SMA X NON ADHERENCE TO ATC INSTRUCTION HAD NMAC IN ATA WITH Y.

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SMA X WAS PRACTICING TOUCH-AND-GOES AT FOUR CORNERS ARPT. AFTER A TOUCH AND GO; TWR THEN CALLED AND INSTRUCTED ME TO RPT R DOWNWIND FOR RWY 23. I COMPLIED; AND BY THE TIME R BASE FOR RWY 23 WAS APPROVED; I HAD ABOUT A 3 MI FINAL. I WAS CLRED FOR THE TOUCH-AND-GO ON RWY 23. THE TWR THEN CAME OVER THE RADIO AND SAID TO MAKE A LOW APCH; TFC IS A SHUTTLE BEHIND YOU. AT THIS POINT; I WAS ABOUT 1 1/2 MI FINAL FOR RWY 23. I TOOK THIS AS LOWER MY GLIDE PATH AND CONTINUE WITH THE TOUCH AND GO AS I HAD TFC BEHIND. HAVING NEVER USED; OR HEARD THE TERM LOW APCH; I DID NOT IDENT A SPECIFIC PROC BUT INSTEAD TOOK IT LITERALLY AS LOWER YOUR APCH TO LNDG. I CONTINUED MY APCH AT 80 KTS AND TOUCHED DOWN AT THE BEGINNING OF THE TOUCHDOWN ZONE. I IMMEDIATELY EXECUTED A SHORT FIELD TKOF AND ROTATED AT 66 KTS; WHICH WAS IMMEDIATELY AFTER I APPLIED FULL THROTTLE. AS I PULLED OFF THE GND AND BEGAN MY CLB; I SPOTTED THE SHUTTLE ABOVE ME APPROX 400 TO 500 FT AND PULLING OFF TO THE L. AT THAT MOMENT I REALIZED THAT SOMETHING HAD GONE WRONG AND THEN THE TWR CAME OVER THE RADIO AND SAID; 'WHEN I TELL YOU DO A LOW APCH; I EXPECT YOU TO DO A LOW APCH.'