Small Aircraft; High Wing; 1 Eng; Fixed Gear
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 1.5
Communication Breakdown; Confusion; Training / Qualification
Conflict NMAC; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Provided Assistance; Flight Crew Took Evasive Action
Human Factors
Aircraft X was inbound from the north east and was given an instruction to fly southbound outside of the pattern from lagoon; our north east inner reporting point at GFK. Aircraft X did not have any problems reading back any of the instruction. Aircraft X reported lagoon when they were about 1 to 2 miles east of the actual reporting point. He was again instructed to fly southbound outside the pattern for runway 17L and I would call his turn into the downwind. When Aircraft X got to lagoon I sequenced him behind a [twin engine aircraft] in the downwind and told him to turn right and enter the downwind. Aircraft X continued southbound and did not turn into the downwind even though I gave him instructions 3 separate times to do so. Aircraft X ended up being a head to head conflict with Aircraft Y who was inbound from our southeast reporting point; power plant; to enter the downwind for runway 17L. I issued traffic to Aircraft Y and he stated he had Aircraft X in sight and said they were flying right at them. I then made several attempts to separate both aircraft but it appeared Aircraft X would do the opposite of what I would tell them. After a near midair collision occurred I was able to turn Aircraft X eastbound to avoid Aircraft Y who was told to enter the downwind. Once Aircraft X was turned northbound [they] attempted to enter the downwind at a 45 degree angle to midfield and would have been a direct conflict with another aircraft who was following Aircraft Y inbound. Aircraft X was again told to remain northbound and I would call all of his turns. Aircraft X landed without incident.Work with FBOs to make sure their instructors are teaching and confirming that their students fully understand pattern entry procedures when inbound to GFK before they are sent on a solo flight. A catastrophic event was avoided by using the help of a local assist who was called up to assist me during a busier than normal hour.Additionally; work needs to be done to look into similar situations that happen at GFK. These situations seem to happen frequently and seem to be quickly discarded as there was no legal loss in separation as GFK is only a class D airspace that deals with primarily VFR aircraft. We at GFK have been extremely lucky that none of these situations have had a bad result but something needs to be looked into on a more broad aspect to prevent them from happening in the future.
GFK Tower Controller reported of a NMAC that happened because a student pilot did not do what they were instructed to do.