WHEN HANDED OFF TO DEP CTL; A PLT DISCOVERS THAT SEPARATION HAS BEEN LOST PROBABLY BECAUSE OF A TURN TO A HDG DIRECT TO THE DEST ARPT WHICH WAS HOW THE CLRNC GIVEN WAS UNDERSTOOD.

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I FILED IFR FROM OJC DIRECT TO 0V3. I RECEIVED MY CLRNC PRIOR TO TAXIING TO RWY 18. WAS CLRED DIRECT TO 0V3; CLB TO 3000 FT; EXPECT 6000 FT 10 MINS AFTER; FREQ 118.9 AND SQUAWK XXXX. AFTER RUN-UP; I PULLED UP TO THE LINE READY FOR TKOF. I CALLED TWR; AND DECLARED READY FOR TKOF. TWR RESPONDED; AND I RESPONDED 'CLRED FOR TKOF.' I RECEIVED NO CORRECTION FROM TWR CONCERNING A HDG. I CLBED OUT TO 500 FT AND DUE TO THE LACK OF AN ASSIGNED HDG; I TURNED OUT TO MY DEST HDG OF 294 DEGS. TWR CALLED AND INSTRUCTED ME TO CONTACT KANSAS CITY DEP. I WENT TO DEP CTL AND WAS GREETED BY A VERY CONCERNED CTLR WHO ASKED ME IF I WAS ASSIGNED A HDG PRIOR TO TKOF. I PROCEEDED TO CLB TO 3000 FT DURING OUR CONVERSATION. I DID NOTICE TFC IN FRONT OF MY ACFT; 600 FT BELOW AND OFF TO THE L OF MY NOSE ON THE TCASII. I CLBED TO 3200 FT FOR BETTER SEPARATION WHILE CONTINUING TO TALK TO DEP. HE INFORMED ME OF THE TFC AT 2000 FT AND CLBING TO 3000 FT. I WAS INSTRUCTED TO CLB TO 4000 FT. LATER; I WAS INSTRUCTED TO CALL ATC AND DID SO. I WAS INFORMED THAT THERE WOULD BE AN INVESTIGATION DUE TO A LACK OF SEPARATION. AFTER RETURNING HOME; I BEGAN TO SCOUR THROUGH THE FARS; TRYING TO FIND INFO AS TO WHAT I MAY HAVE DONE WRONG. I CONTACTED MY IFR INSTRUCTOR AND EXPLAINED THE EVENT. I HAVE COME TO THE CONCLUSION THAT I SHOULD HAVE ASKED FOR A HDG PRIOR TO TKOF RATHER THAN ASSUMING THAT I WAS CLRED TO TURN OUT; AND I SHOULD HAVE REMINDED TWR THAT I WAS DEPARTING 'IFR' WHEN I CALLED UP TO ANNOUNCE THAT I WAS READY FOR TKOF. I DO BELIEVE THAT THE JOHNSON COUNTY CTLRS ARE AMONG THE BEST IN THE NATION AND I AM VERY CONCERNED THAT THE CTL TWR AT OJC MAY BE REPRIMANDED FOR MY LACK OF EXPERIENCE. I HAVE ABOUT 6 ACTUAL IFR TRIPS UNDER MY BELT.