SR22
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 6
Distraction; Situational Awareness; Training / Qualification
Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Procedure; Aircraft; Human Factors
Aircraft Y was cleared for the RNAV 24 approach at FIN. He was at 016 prior to the FAF and switched to FIN ATCT. Aircraft X was on a vector for the RNAV 24 approach at 030 and much faster than Aircraft Y. I told Aircraft X to expect a vector across the final approach course for spacing and that he was #2 for the airport following Aircraft Y at his 2 o'clock and two miles. Aircraft X reported the aircraft in sight. The Certified Professional Controller-In Training I was training began talking to another aircraft. I noticed Aircraft X turn toward FIN and descend. I keyed up and issued him a turn away from traffic and issued a climb back up to 030 but separation had been lost. Aircraft X turned and descended without clearance and I asked if he wanted to cancel IFR. Aircraft X cancelled IFR and proceeded VFR to FIN.I have no recommendations.
DAB Controller was instructing a Certified Professional Controller-In Training. One aircraft was given a heading and altitude to maintain; but was much faster than traffic it was following. Aircraft turned towards the traffic it was following and separation was lost.