Date: 201902
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: PA-28 Cherokee/Archer/Dakota/Pillan/Warrior
Operator: FBO
Operating under: Part 91
Mission: Training
Flight phase: Initial Approach
Airspace: Class D ZZZ
ATC / advisory: Tower ZZZ
Second aircraft: Regional Jet 200 ER/LR (CRJ200)
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Distraction; Situational Awareness
Second reporter function: Instructor
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action; Flight Crew Executed Go Around / Missed Approach; Flight Crew Became Reoriented; General Flight Cancelled / Delayed
Contributing factors: Human Factors; Airport
Primary problem: Human Factors

Narrative: Aircraft X entered the VFR traffic pattern from the northeast. They were sequenced to follow traffic midfield downwind. They reported traffic in sight and I visually observed them following instructions. I was scanning and working other aircraft when Aircraft X was on base for Runway XXR. I sequenced another aircraft to follow them. I looked back at Aircraft X and observed Aircraft Y climbing to avoid them as Aircraft X had lined up on approach for Runway XXL. I corrected the situation and confirmed Runway XX Right with Aircraft X again; while the other controller issued missed approach instructions to Aircraft Y. I believe the pilot simply became confused and didn't ask for clarification. If the pilot is unsure of the runway intended for them to land on; they could ask Tower to verify before that situation occurs again.


Second narrative: We entered downwind for Runway XXR right traffic. Tower instructed us to extend our downwind; and that they would call our turn to base for Runway XXR. When Tower called our base leg we turned west and began our descent from pattern altitude. I told my student to 'square the base' and continue flying west. I lost situational awareness outside of the aircraft and did not realize that the airport road or Runway XXL was what I was interpreting to be Runway XXR. I looked up and saw a CRJ-200 to the left and above us. I even verbalized this out loud; and then soon realized that they appeared to be closer than they should be if we were truly lining up with Runway XXR.That is when I intervened and corrected to the north immediately. I realized that I had not been looking at Runway XXR; I had been looking at Runway XXL. Once established northbound I realized my error; and this is about when Tower came on to query what runway we were lining up for. Factors that may have contributed to this were that Runway XXR was plowed for the most part; but I would say you could only see runway pavement extended out from centerline about 5 feet either side. With the extension of our downwind; Runway XXR was not where it usually is when speaking in terms of sight picture; and I believe this contributed to our overshoot of Runway XXR. When on the base leg; my eyes just locked on to the largest; most visible surface that appeared to be a runway; which happened to be Runway XXL. This was a huge mistake that I take full responsibility for; and I am not taking it lightly. Please do not hesitate to contact me with any further questions.


Synopsis: A Tower Controller and pilot reported the pilot lined up with the wrong runway which caused another aircraft to take evasive action and go around.