Commercial Fixed Wing
Air Traffic Control Developmental
Communication Breakdown
ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Runway
Air Traffic Control Issued Advisory / Alert
ATC Equipment / Nav Facility / Buildings; Weather
Aircraft X was holding short of November on Romeo. Runway 4 [was under Ground Control] for taxiing and not being used for departures. I gave instructions for Aircraft X to turn right on Runway 4 and hold short of Runway 13R. The pilot's first read back was unconvincing so I restated instructions. The second read back was acceptable. I asked pilot to advise when holding short of Runway 13R due [to] visibility being very low. Shortly after Aircraft X advises holding short of Runway 13R. I acknowledged with 'Roger.' I gave taxi instructions to Aircraft Y; which just exited Runway 13R. Immediately after Aircraft Y read back; Aircraft X advises he is at Runway 4 at N3. I said 'Say Again'. Aircraft X again advised on Runway 4 at N3 which is on other side of Runway 13R. I issued the Brasher warning and the pilot called in.[I recommend] installing ASD-X at San Antonio airport.
SAT Ground Controller reported that an aircraft taxied across an active runway during low visibility conditions.