C172 ACFT ON APCH HAD ANOTHER C172 DSNDING ON TOP OF HIM. TWR CTLR INTERVENED WITH AN EVASIVE HDG FOR RPTR AND OTHER ACFT ALSO TURNED IN RESPONSE TO THE CLRNC. APPARENTLY; THE FOLLOWING ACFT DIDN'T KNOW HIS SEQUENCE AND BECAME CONFUSED WITH RPTR ACFT INSTRUCTIONS.

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THE PROB AROSE WHEN THE C172 ACFT Y BEHIND AND ABOVE ME DID NOT SEE AND AVOID. I WAS FLYING A C172 ACFT X AND WAS CLRED TO LAND BEHIND A C172 XING THE NUMBERS OF RWY 16 AT PWK (ACFT Z). ACFT Y WAS TO FOLLOW ME (ACFT X). AT 1000 FT MSL I RECALL SEEING THE VASI; RED OVER WHITE. THE TWR CALLED ME AND ASKED MY ALT. I ADVISED 1000 FT. I WAS THEN TOLD TO MAKE AN IMMEDIATE L 360 DEG TURN. AS I INITIATED MY TURN TO THE L I SAW THE BOTTOM AND R SIDE OF ACFT Y. ACFT Y WAS TURNING TO THE L AS WELL. ACFT Y NEARLY DSNDED ON TOP OF ME PRIOR TO THE L TURN. ON SEP/XA/97 I MET WITH THE TWR CHIEF AT PWK. WE LISTENED TO THE TWR TAPE AND CONFIRMED THAT THE CTLR SAW ACFT Y DSNDING ON ACFT X AND TOOK THE APPROPRIATE STEPS. THE PLT IN ACFT Y FAILED TO SEE AND AVOID (ACFT Y HAD A STUDENT PLT AND AN INSTRUCTOR). I CALLED THE INSTRUCTOR OF ACFT Y ABOUT 50 MINS AFTER THE INCIDENT. HE SAID HE THOUGHT HE WAS #2. HE STATED HE DID NOT SEE ACFT X UNTIL HE LOOKED OUT OF HIS WINDOW TO CONFIRM THAT THE GEAR WAS DOWN. (EVEN THOUGH HE WAS IN A FIXED GEAR C172). THE TWR TAPE REVEALS ACFT M WAS CLRED FOR A TOUCH-AND-GO ON RWY 16. ACFT Z WAS BEHIND ACFT M; ACFT X BEHIND ACFT Z; AND ACFT Y WAS TO BE BEHIND ACFT X. I HAD THE BEACON AND LNDG LIGHT ON.