RPTR CLRED ACFT X ONTO ACTIVE RWY. BECAME BUSY DISTR; FORGOT ABOUT ACFT X. ACFT Y CALLED FOR CLRNC TO LAND ON SAME RWY. RPTR CLRED ACFT Y TO LAND. LATER; RPTR REALIZED RWY WAS OCCUPIED; TOLD ACFT Y TO GO AROUND.

Narrative

I WAS WORKING THE LATE NIGHT SHIFT IN THE TWR DURING A PERIOD OF MODERATE TFC. THE S COMPLEX OF THE ARPT WAS OBSCURED FROM THE TWR BY HVY GND FOG. THE N COMPLEX WAS CLR WITH RVR OF MORE THAN 6000 FT. DUE TO THE WX AND NOISE ABATEMENT; THE INBOARD RWY ON THE N COMPLEX WAS THE ONLY ONE IN USE FOR TKOF AND LNDG. I ISSUED TAXI INTO POS AND HOLD INSTRUCTIONS TO AN ACFT (ACFT X) AWAITING DEP AS A PREVIOUS ARR ROLLED OUT ON THE RWY. I BECAME DISTR BY GND CTL DUTIES; IN PARTICULAR; BY 2 ACFT WITH SIMILAR CALL SIGNS WHO CONFUSED THEIR TAXI INSTRUCTIONS. AS I RESOLVED THE SIT; AN ACFT (ACFT Y) CALLED INBOUND ON FINAL. I CLRED ACFT Y TO LAND FORGETTING THE FIRST ACFT X WAS HOLDING IN POS. AS THE SECOND ACFT Y APCHED SHORT FINAL; I SCANNED THE RWY NOTICING THE FIRST ACFT X STILL IN POS; AND SENT THE SECOND ACFT Y AROUND. THE PLT EXECUTED THE GAR AND PASSED OVER ACFT X IN POS AT APPROX 300 FT. AT THE TIME OF THE INCIDENT I HAD BEEN AWAKE FOR OVER 24 HRS; ON POS AND ALONE IN THE TWR FOR ALMOST 2 HRS; AND WAS SOLELY RESPONSIBLE FOR ALL TWR CAB FUNCTIONS. WHILE THIS IS NOT NORMAL PRACTICE; THE WX WAS ALSO A CONTRIBUTING FACTOR TO THE WORKLOAD AS I HAD TO PAY PARTICULAR ATTN TO THE S AREA SURFACE DETECTION EQUIP (ASDE) TO ENSURE SAFETY OF THE ACFT TAXIING ON THE S COMPLEX. HAD THERE BEEN A SECOND CTLR IN THE TWR TO SHARE OPERATIONAL RESPONSIBILITIES; AS THERE NORMALLY IS; I AM CONFIDENT THIS INCIDENT WOULD NOT HAVE OCCURRED.