Narrative:

I started my shift and was receiving a briefing to relieve the local control position. As I was listening to the briefing I noticed an aircraft on short final (almost over the numbers) for runway 32. I picked up the binoculars to check for gear. This was about 1 minute into my shift; less than 1 minute into the briefing and had not yet gotten to the current traffic portion. As I was looking [local] stated that he had not cleared that aircraft to land. By this time it was too late to get the light gun out and the aircraft had already touched down. It was at this point I noticed a second aircraft on final for runway 32 and picked up the portable radio we have in the cab and dialed in sgs unicom freq. I reached out and was able to raise both aircraft on the sgs freq. Both aircraft were on discreet beacon codes that were flashing on the radar display indicating no flight plan with that code. I determined that aircraft X was rolling out on runway 32 and a [high wing] was on final for runway 32. Both thought they were at sgs. I identified myself as the tower at stp and for both of them to change to my freq 119.1. I told aircraft X to turn left at the end and advise intentions to which he responded that he wanted to taxi for takeoff and go to sgs. The cessna advised that he was going around and heading for sgs. I made sure the cessna had sgs in sight and gave a freq change. I coordinated with ground control and taxied the aircraft back to runway 32 for departure. I gave him the possible pilot deviation warning and the tower phone number with a request to call as soon as practical. No other aircraft were on the runway and no loss of separation occurred.I cleared the aircraft for takeoff and he departed for sgs. When he called he spoke to the controller in charge who was the controller I just took over local control from. The pilot stated that they were IFR to sgs and were given 'vectors to the runway'. M98 was notified of the situation. At the point of both aircraft successfully on their way to sgs I thought I was dealing with lost VFR pilots. It was only after that I put it together that two consecutive lost aircraft on discreet beacon codes was very unusual. Many pilots that fly to sgs mistake stp for their intended destination. M98 advised later that the aircraft had been vectored from the south to sgs and canceled IFR about 8 miles out. They overflew sgs and proceeded to stp not realizing it was the wrong airport.M98 should point out all IFR arrivals into sgs; regardless of what direction they are being vectored in from. That way we will be aware of the potential for confusion between our airports and be mindful of those aircraft after they cancel and have been given a freq change to unicom.

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Original NASA ASRS Text

Title: STP Tower Controller reported an aircraft landed at the wrong airport and a second aircraft went missed approach. Both aircraft were lined up for the wrong airport. Pilot that landed on the wrong airport also reported the event.

Narrative: I started my shift and was receiving a briefing to relieve the local control position. As I was listening to the briefing I noticed an aircraft on short final (almost over the numbers) for RWY 32. I picked up the binoculars to check for gear. This was about 1 minute into my shift; less than 1 minute into the briefing and had not yet gotten to the current traffic portion. As I was looking [local] stated that he had not cleared that aircraft to land. By this time it was too late to get the light gun out and the aircraft had already touched down. It was at this point I noticed a second aircraft on final for RWY 32 and picked up the portable radio we have in the cab and dialed in SGS Unicom freq. I reached out and was able to raise both aircraft on the SGS freq. Both aircraft were on discreet beacon codes that were flashing on the radar display indicating no flight plan with that code. I determined that Aircraft X was rolling out on RWY 32 and a [high wing] was on final for RWY 32. Both thought they were at SGS. I identified myself as the tower at STP and for both of them to change to my freq 119.1. I told Aircraft X to turn left at the end and advise intentions to which he responded that he wanted to taxi for takeoff and go to SGS. The Cessna advised that he was going around and heading for SGS. I made sure the Cessna had SGS in sight and gave a freq change. I coordinated with GC and taxied the aircraft back to RWY 32 for departure. I gave him the possible pilot deviation warning and the tower phone number with a request to call as soon as practical. No other aircraft were on the runway and no loss of separation occurred.I cleared the aircraft for takeoff and he departed for SGS. When he called he spoke to the CIC who was the controller I just took over LC from. The pilot stated that they were IFR to SGS and were given 'vectors to the runway'. M98 was notified of the situation. At the point of both aircraft successfully on their way to SGS I thought I was dealing with lost VFR pilots. It was only after that I put it together that two consecutive lost aircraft on discreet beacon codes was very unusual. Many pilots that fly to SGS mistake STP for their intended destination. M98 advised later that the aircraft had been vectored from the south to SGS and canceled IFR about 8 miles out. They overflew SGS and proceeded to STP not realizing it was the wrong airport.M98 should point out all IFR arrivals into SGS; regardless of what direction they are being vectored in from. That way we will be aware of the potential for confusion between our airports and be mindful of those aircraft after they cancel and have been given a freq change to Unicom.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.