CONTINUING AND RECURRING COMMUNICATION PROBS RPTED AT THE CHARLESTON AFB/INTL ARPT BTWN THE TWR AND C17.

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ACFT X AND ACFT Y WERE TAXIED INTO POS TO HOLD ON RWY 15 AT DIFFERENT TIMES. AFTER ACFT ARE IN POS THEY CAN RECEIVE CHS TWR; BUT WE (CHS TWR) CANNOT HEAR THEM THIS IS ON GOING WITH THE C17 AND IS CAUSING PROBS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR IS CONCERNED THAT A HAZARD WILL DEVELOP WHEN CLEARANCES ARE ISSUED THAT ARE APPARENTLY RECEIVED; BUT NOT ACKNOWLEDGED EVEN THOUGH THEY ARE EXECUTED BY THE ACFT. USUALLY THE EXECUTION OF THE CLRNCES FOR TKOF OR TAXI IS DONE IN TIMELY FASHION AND THE CREW MOST LIKELY HAS RESPONDED NOT BEING AWARE THAT IT HAS NOT BEEN RECEIVED IN THE TWR. OTHER TIMES THERE IS SOME DELAY CAUSING POTENTIAL TFC PROBS. THE AREAS OF CONCERN ON THE ARPT ARE THE ENDS OF RWY 15 AND 03; AS WELL AS; THE TXWYS BTWN THOSE TWO RWYS. THE AREAS AROUND RWY 21 AND 33 ENDS DO NOT SEEM TO BE A RECURRING PROB. WHEN THIS ACFT WAS ORIGINALLY BASED AT THIS JOINT USE ARPT THERE WAS NO PROB; BUT APPARENTLY THERE HAVE BEEN SOME MODIFICATIONS MADE SINCE THAT TIME TO THE ACFT SYSTEMS. THE RPTR INDICATED THAT HE HAS ANECDOTAL EVIDENCE THAT THERE ARE OTHER ARPTS HAVING THE SAME COMMUNICATION PROB WITH THE C17 DURING GROUND OPS.