Air Traffic Control Developmental
Confusion; Situational Awareness; Training / Qualification
ATC Issue All Types; Conflict Airborne Conflict
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Airspace Structure; Human Factors; Procedure
I was working Local Control. Aircraft X checked in northeast of the CRP VOR on the VOR Approach. I read Aircraft X the winds and cleared Aircraft X for the option to Runway 18. Aircraft X read back the option clearance. The only other traffic I saw in the area was Aircraft Y north of NGP heading northwest on a downwind at 1;600 feet for NGP Runway 13R on North radars tag. Aircraft Y had NGP in the scratch pad; as well as the symbol for the RNAV Approach.After clearing Aircraft X for the option and seeing the only traffic in the area was going to NGP I started looking out the window; to acquire Aircraft X visually and check for gear. After approximately thirty seconds to one minute Aircraft X asked if I had traffic out here for him. As I looked up at the scope the collision alarm went off. Aircraft X was over the CRP VOR at 1;600 feet still on the VOR 18 approach. Aircraft Y was approximately one mile south of the CRP VOR still northwest bound at 1;600 feet. I immediately issued a traffic alert to Aircraft X; 'traffic alert Aircraft X traffic 12 o'clock less than a mile Aircraft Y northwest bound same altitude suggest you climb immediately.' Aircraft X's response was 'roger; he's no factor now'. I asked Aircraft X if he wanted vectors to be re-sequenced; and he said no he would rejoin the approach on his own. I told Aircraft X traffic no factor and cleared him for the option again. Aircraft Y was vectored behind Aircraft X into NGP without further incident.I would recommend to myself never assume that because someone else is talking to the other aircraft and it's going to another airport it's not going to be a factor.
CRP Local Controller reported observing an aircraft going to an adjacent airport fly into his airspace on a conflicting heading with an aircraft conducting an approach.