ACR APCH TO CLOSED PORTION OF RWY WITH DISPLACED THRESHOLD DUE TO POOR MARKINGS.

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AN MD88 ATTEMPTED TO LAND ON A PORTION OF RWY 21 AT GSP THAT WAS UNDER CONSTRUCTION. I BELIEVE THE ACFT WOULD HAVE DONE SO HAD I NOT ISSUED A SAFETY ADVISORY. I AM FILING THIS RPT BECAUSE I HAVE BEEN TOLD BY NUMEROUS OTHER CTLRS THAT THIS HAS HAPPENED TO THEM AS WELL. RWY 21 IS BEING LENGTHENED FROM 7600 FT TO 9000 FT. CONSTRUCTION HAS BEEN UNDERWAY FOR ABOUT 9 MONTHS; AND IS NEARING COMPLETION. CONTRIBUTING FACTORS: GS OTS. VASI OTS. RWY NUMBER IS FADED AND VERY DIFFICULT TO SEE. NOTAMS/ATIS ARE CONFUSING; EG; THRESHOLD IS ADVERTISED AS 'DISPLACED' WHEN IT REALLY IS 'RELOCATED' (AIM 2-3-2). NO 10 FT WIDE THRESHOLD BAR ACROSS RWY AS RECOMMENDED IN AIM. NO MARKINGS EXIST IN THE CONSTRUCTION AREA TO INDICATE THE RWY IS CLOSED. FACILITY AND ARPT MGMNT HAVE BEEN UNRESPONSIVE TO CONCERNS VOICED BY PLTS AND CTLRS; EG; THE ACR DIRECTOR OF FLT OPS ASKED FOR IMPROVEMENTS TO THE SIT; AND FOR THE MOST PART THEY WERE NOT MADE. THE OTHER END OF THE RWY WILL BE EXTENDED NEXT YR. WHILE IT MAY BE TOO LATE TO CORRECT THE CURRENT PROB; PERHAPS THIS WILL PREVENT SOMETHING UNFORTUNATE FROM HAPPENING NEXT YR.