Date: 201604
Local time of day: 1801-2400
Location: STP.Tower, MN
Flight conditions: VMC
Light: Daylight
Aircraft: Amateur/Home Built/Experimental
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Landing
ATC / advisory: Tower STP
Second aircraft: Small Aircraft; High Wing; 1 Eng; Fixed Gear
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Confusion; Distraction; Situational Awareness
Second reporter function: Single Pilot
Anomaly: Airspace Violation All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Landing Without Clearance; Ground Incursion Runway
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Provided Assistance
Contributing factors: Airport; Procedure; Human Factors
Primary problem: Procedure

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.


Second narrative: My friend and I planned a flight to deliver his [high wing] to SGS for float installation where I was to pick him up and fly him back. He left VFR from ZZZ; I left IFR filed IFR at ZZZ and left a half hour later. I was IMC for most of the flight at 4;000 feet. I had never been into SGS before as we got close Center reported traffic and vectored me away from SGS I started looking for traffic; Center gave me more vectors. Then I believe gave me a visual approach and reported when I could cancel IFR while looking for traffic I spotted a runway in front of me I assumed was SGS. I cancelled and switched to SGS Unicom. I continued in and just about touchdown I realized I was at STP not SGS.I usually always file IFR especially in busy controlled airspace and have never been vectored to line up with the wrong airport. In this area I would think that the controller would be more careful vectoring IFR traffic so near a Class D airport making sure the plane is lined up with the right airport. I have flown for over 30 years and have never violated an airspace ever flying several times in DC's SFRA Airspace successfully.


Synopsis: 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.