SMA ON AN ILS RWY 32 WAS INSTRUCTED TO RPT THE LOM INBOUND AFTER HE RPTED HE WAS AT THE IAF ON HIS FIRST CALL. GND CTLR COORD FOR A BE55 TO CROSS THE ACTIVE RWY AT THE APCH END AND THIS WAS APPROVED. THE BE55 SAW THE LNDG LIGHTS ON THE SMA AND HELD HIS POS. THE RPTR THEN SAW THE SMA IN HIS FLARE AND LNDG WITHOUT A CLRNC. THE SMA HAD GIVEN AN INACCURATE POS RPT AND THE VIGILANT BE55 SAVED A SERIOUS INCIDENT FROM OCCURRING.

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I WAS WORKING LOCAL WITH WX AT IFR; WIND CALM; VISIBILITY HALF MI; RWY 32 RVR 3500 FT; FOG; OVCST 002; TEMP 6 DEGS; DEWPOINT 5 DEGS; ALTIMETER 29.97. SMA X WAS CALLED IN ON THE ILS RWY 32 FROM ZOA. ETA XA13Z. SMA X RPTED INSIDE COOTI (IAF). I TOLD THE ACFT TO RPT MONES OM INBOUND. GND CTL ASKED FOR A RWY XING FROM THE APCH END OF RWY 32 WBOUND TO TXWY D. LUCKILY THE XING ACFT SAW THE LNDG LIGHTS OF SMA X AND IMMEDIATELY STAYED CLR OF THE RWY. SMA X WAS INSIDE MONES; NOT COATI; AS HE RPTED ON HIS INITIAL CALLUP. MONES IS ACTUALLY 5.8 DME OUT ON THE ILS. SO BY THE TIME I WAS EXPECTING A CALL OVER THE OM MONES; THE ACFT WAS ALREADY FLARED OUT OVER THE RWY THRESHOLD. STS IS A NON RADAR VFR TWR; WE DO NOT HAVE A BRITE SCOPE AS A REF EITHER; SO CORRECT POS RPTS ARE ESSENTIAL TO SAFE OP. SMA X SHOULD HAVE HAD A BETTER IDEA OF WHERE HE WAS ON THE ILS APCH; AND ABOVE ALL ELSE; SHOULD HAVE ASKED FOR PERMISSION TO LAND. LUCKILY FOR EVERYONE; THE XING BARON SAW THE LNDG LIGHTS OF SMA X AND PREVENTED A DISASTER.