NMAC AND LESS THAN STANDARD SEPARATION BETWEEN ACR AND SMA IN TRAFFIC PATTERN. PLT DEVIATION AND PROBABLE OPERATIONAL ERROR.

Narrative

WE WERE CLRED FOR TKOF RWY 18 AT MSN. AS PWR WAS BEING BROUGHT UP FOR TKOF; THE S/O ASKED; 'DO YOU HAVE THAT GUY?' IT TOOK ME (CAPT) A WHILE TO PICK UP SMA Y THAT HAD MADE A TOUCH AND GO LNDG ON RWY 22 AND WAS JUST GOING W OF RWY 18 CENTERLINE IN FRONT OF US. SMA Y WAS INSTRUCTED BY TWR TO MAKE RIGHT TFC; WHICH WOULD HAVE CLRED OUR FLT PATH ON TKOF. INSTEAD SMA Y MADE A LEFT TURN IN FRONT OF US AT ABOUT 200-300' AGL AS WE WERE ROTATING. I INSTRUCTED THE COPLT (WHO WAS MAKING THE TKOF) TO GO RIGHT AS WE WERE LEAVING THE RWY TO MISS ACFT Y. WE PASSED HIM LEVEL WITH ABOUT 300-400' LAT SEP. I FEEL THAT THE THIRD PLT'S (I.E.; S/O) OBSERVATION AND CALLOUT MIGHT POSSIBLY HAVE PREVENTED A MIDAIR. I ALSO THINK IT WOULD BE A GOOD IDEA FOR TWR TO WAIT UNTIL THEIR INSTRUCTIONS HAVE BEEN COMPLIED WITH BEFORE CLEARING ANOTHER ACFT FOR TKOF WHERE A CONFLICT EXISTS IF THE OTHER ACFT DOESN'T COMPLY. SUPPLEMENTAL INFO FROM ACN 93362: FOLLOWING THE THIRD TOUCH AND GO ON RWY 22 ATC DIRECTED US TO FLY WHAT WE UNDERSTOOD AS LEFT TFC AFTER ATC CONFUSED OUR TAIL # WITH THAT OF ANOTHER ACFT MOMENTARILY. AS WE TURNED LEFT DOWNWIND FOR RWY 22; ATC HAD ALREADY CLRED ACR X TO TAKE OFF ON RWY 18; NOT NOTICING THAT WE WERE FLYING LEFT INSTEAD OF RIGHT TFC; WHICH IT TURNED OUT WE WERE INSTRUCTED TO FLY.