ILM CTLR INVOLVED IN OPERROR WHEN 2 C182'S DEPART FROM DIFFERENT RWYS SIMULTANEOUSLY WITH SIMILAR CALL SIGNS.

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ACFT Y CALLED READY FOR DEP ON RWY 17; AND I INSTRUCTED HIM TO HOLD SHORT. ACFT X CALLED READY FOR DEP ON RWY 35. AND INSTRUCTED HIM TO HOLD SHORT. I INSTRUCTED ACFT Y TO TAXI INTO POS AND HOLD RWY 17 (DUE TO TFC ON RWY). WHEN THE RWY 24 OP WAS COMPLETE; I INSTRUCTED ACFT Y TO FLY RWY HDG AND CLRED HIM FOR TKOF ON RWY 17. ACFT Y WAS AIRBORNE (CLBING); AND NO LOWER THAN 500 FT AGL; WHEN I OBSERVED A CESSNA AT TAXI SPD ON RWY 35 ABEAM THE TWR. SUPPLEMENTAL INFO FROM ACN 481606: I REQUESTED MY IFR CLRNC TO CHAPEL HILL (IGX). AFTER READING BACK THE CLRNC; I ADVISED GND CTL I WAS READY TO TAXI. I REQUESTED A TKOF ON RWY 35 IF TFC PERMITTED. I HEARD AN ACFT REQUEST AND RECEIVE CLRNC TO TAXI TO RWY 17. GND CTL THEN CALLED ME TO VERIFY MY CALL SIGN. WHEN THE RUNUP WAS COMPLETE; I CHANGED TO WILMINGTON TWR FREQ AND BEGAN TO TAXI INTO A POS SHORT OF RWY 35. WITHIN SECONDS; THE TWR CLRED TO FLY RWY HDG AND CLRED FOR TKOF ON RWY 35. I REPEATED TO TWR THAT I WAS CLRED FOR TKOF ON RWY 35 AND TO FLY RWY HDG. (I ALWAYS REPEAT INSTRUCTIONS AND CLRNCS TO MAKE SURE THAT THERE CAN BE NO MISUNDERSTANDING.) THERE WAS NO QUESTIONING OF MY READBACK. I TAXIED ONTO THE RWY AND BEGAN MY TKOF. I WAS JUST A FEW HUNDRED FT DOWN THE RWY WHEN I SPOTTED AN ACFT THAT WAS AIRBORNE SEVERAL HUNDRED FT IN THE AIR; CLBING ON A HDG OF APPROX 160 DEGS ON A COURSE WELL TO THE L OF RWY 17 AND NOT A THREAT TO ME ON MY TKOF ROLL OR CLB OUT COURSE. MY IMMEDIATE THOUGHT WAS THAT THE ACFT WAS ON A MISSED APCH OR A GAR. THE ACFT CONTINUED TO CLB OUT ON A SOUTHEASTERN COURSE; AND WAS PAST ME BEFORE I HAD ROLLED 2000 FT. AFTER I WAS AIRBORNE AND CLBING OUT; THE TWR GAVE ME INSTRUCTIONS TO TURN L ON A WESTWARD TRACK AND INFORMED ME THAT I WAS TO CALL THE TWR SUPVR UPON LNDG. EVEN THOUGH I HAD RECEIVED A CLRNC TO MY DEST; I ELECTED TO RETURN TO THE RAMP IMMEDIATELY TO CALL THE TWR SUPVR. IT WAS NOT UNTIL CALLING THE SUPVR THAT I BECAME AWARE THAT ANOTHER ACFT HAD TAKEN OFF ON RWY 17. AT THAT TIME; THE SUPVR TOLD ME THAT HE HAD REVIEWED THE TAPE 4 TIMES AND THAT THERE WERE SOME PROBS IN THE TWR. WHEN QUERIED FURTHER; HE ACKNOWLEDGED THAT EVEN THOUGH I WAS STEPPED ON IN MY XMISSION; I DEFINITELY HAD CALLED THE TWR TO ACKNOWLEDGE A CLRNC THAT I WAS CLRED FOR TKOF ON RWY 35 AND THAT CALL WAS NEVER CHALLENGED. HE ALSO NOTED THAT THE SIT WAS AGGRAVATED BY THE FACT THAT THE OPERATOR WAS TALKING TO SEVERAL ACFT THAT HAD VERY SIMILAR CALL SIGNS.