COMMUTER FLT INBOUND TO TYS TOOK EVASIVE ACTION TO AVOID A GLIDER OPERATING NEAR THE EDGE OF CLASS C AIRSPACE ON FINAL APCH.

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AT APPROX XA00 LCL TIME; I WAS WORKING RADAR W APCH/DEP CTL AT TYS. THERE WAS KNOWN GLIDER ACTIVITY AT THE DKX ARPT LOCATED 10 MI NE OF TYS. THIS ARPT (DKX) IS DIRECTLY ON THE FINAL FOR RWY 23R&L AT TYS. I HAD AN ACFT X FLT (A CARJ) ON A 140 DEG HDG 10 MI N OF THE ARPT ON BASE LEG. I CALLED TFC 12 O'CLOCK; 4 MI; ALT UNKNOWN. ACFT X ADVISED TFC IN SIGHT; IT'S A GLIDER AT OUR ALT AND WE ARE TURNING. EVASIVE ACTION BY THE PLT WAS NEEDED TO AVOID A COLLISION. NONE OF THE GLIDERS HAVE XPONDERS. BY THE BOOK; THE GLIDERS ARE LEGAL BECAUSE THEY ARE OUTSIDE OF THE CLASS C AIRSPACE. THIS IS NOT THE FIRST TIME THIS HAS HAPPENED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THE GLIDER ACTIVITY IS VERY HVY ON WKENDS AND HOLIDAYS. THEY ARE NOT EQUIPPED WITH RADIOS OR XPONDERS AND PRETTY MUCH OPERATE AT 5000 FT AND BELOW. FOR THE MOST PART; THEY CONDUCT THEIR OPS JUST OUTSIDE OF THE CLASS C AIRSPACE. RPTR SAID THERE ARE INCIDENTS JUST ABOUT EVERY WKEND INVOLVING GLIDERS AND TFC INBOUND TO TYS. AS MUCH AS POSSIBLE; CTLRS TRY TO STAY CLR OF THE AREA WHEN VECTORING ACFT. UNION REPRESENTATIVE HAS BEEN TO THE GLIDER ARPT TO TALK TO PLTS BUT NOT MUCH HAS COME OUT OF THE DISCUSSIONS. ASKED THE RPTR IF THE PLT OF THE REGIONAL JET; MENTIONED IN HIS RPT; HAD FILED AN NMAC. THE RPTR SAID THE PLT WAS TALKED OUT OF FILING AN NMAC.