Date: 201710
Local time of day: 1201-1800
Location: TUL.TRACON, OK
Flight conditions: VMC
Aircraft: Light Transport
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class D RVS
ATC / advisory: Tower RVS
Second aircraft: Small Aircraft; High Wing; 1 Eng; Fixed Gear
Reporter organization: Government
Reporter function: Approach
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness
Second reporter function: Local
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic; Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance
Contributing factors: Procedure; Human Factors; Manuals
Primary problem: Human Factors

Narrative: Aircraft X had been vectored for a visual approach into RVS. I cleared him for the Approach 9 southwest of RVS. He was on a 080 vector and level at 2;500 feet when cleared and switched to RVS Tower. I had climbed Aircraft Y to 3;500 feet to top Aircraft X. After just a minute or so I notice Aircraft X's altitude indicating 2;700 feet and climbing. I call RVS via the shout line and tell them to get him back down. I didn't turn Aircraft Y immediately; anticipating Aircraft X to rush back down. I did a projection and it showed 2.92 miles. I turned Aircraft Y to the southwest to get diverging courses.The event occurred because Aircraft X climbed after being at 2;500 feet and cleared for a visual approach. The pilot when he called; told the Supervisor that he was on a visual approach and he can climb. First I ever heard of this; and it would significantly change how we do visual approaches if true. Seems like a pilot just wasn't paying close enough attention and let the aircraft climb; due to his error or maybe the autopilot. He then tried to make an excuse for his mistake. The pilot had been given 2;500 feet; acknowledged and verified it; and had descended to that altitude prior to the clearance. Remind the pilot of the rules and that should suffice. If the pilot is correct that he can climb on a Visual Approach clearance; the agency needs to brief all Controllers as soon as possible on this.


Second narrative: Aircraft Y departed IFR from RVS on a 300 heading. I switched him to TUL departure. Aircraft X was cleared for the visual approach from the south to RVS. Shortly after TUL Approach called and told me to tell Aircraft X to descend back to 2;500 feet immediately because Aircraft X had climbed to 3;000 feet after being descended to 2;500 feet and cleared for the visual approach. Aircraft Y had been climbed to 3;500 feet and turned south by Approach. I told Aircraft X to descend to 2;500 feet and called traffic. 1;000 feet and 3 miles was lost. After Aircraft X landed and I taxied him to parking; I issued the brasher.Aircraft X thought he could climb once he vacated an altitude on a visual approach.


Synopsis: A Tower and TRACON Controller reported an aircraft on a visual approach climbed unexpectedly which put it into confliction with departing traffic.