A Tower Local Controller and TRACON Departure Controller reported the Local Controller issued a vector off course to an aircraft on short final which placed it below the Minimum Vectoring Altitude.
Synopsis
A Tower Local Controller and TRACON Departure Controller reported the Local Controller issued a vector off course to an aircraft on short final which placed it below the Minimum Vectoring Altitude.
Narrative
Aircraft X on the final approach course for the VOR approach to Runway XX circle to Runway YY. Aircraft Y was executing climb out which was issued as runway heading and VFR but only read back to the radar Controller as VFR without a restriction. Aircraft Y was switched to Departure prior to us noticing that they had turned southeast bound. I was no longer talking to Aircraft Y but Aircraft X was on my frequency so I cancelled their approach clearance and turned them to a 220 heading however I didn't give them an altitude to maintain and they were below the minimum vectoring altitude. I was not aware that Aircraft Y was VFR on their climb out so there was no loss of separation. Better communication between the radar and local Controller. Another Controller called down to the TRACON and was coordinating and relaying information instead of me directly. I was hesitant to assign an altitude when I wasn't sure what Aircraft Y was doing but I should have assigned the MVA as soon as I vectored them off the approach and canceled their approach clearance. I wasn't aware the aircraft was VFR and if I would have known I wouldn't have cancelled the approach clearance.
Second reporter narrative
I had several practice approaches. Aircraft Y was doing a circle to Runway YY; followed by another Aircraft Z doing same approach; followed by an Aircraft X doing a VOR/DME XX circle to Runway YY. Aircraft Y said they wanted to fly VFR to ZZZ1 on the go. I issued 'fly runway heading; maintain VFR'. I misheard read back; they read back 'maintain VFR'. Aircraft Y; on departure; turned southeast towards the Aircraft X. They were maintaining VFR and the closest they got was 500 ft. and 3.1 miles. The Local Controller issued a turn to the Aircraft X at 1600 ft. busting MVA. Missing the read back was primary cause of the event. I also issued the runway heading speaking faster than I normally would; which was mainly due to being busier than I have been in last couple of months. I will also say that a lot of Controllers would have issued 'turn left to ZZZ1; maintain VFR' for the climb out. If that was issued the Aircraft Z would have did the same thing. I wanted to keep it simple since I was busy. The military quite often as of late says they want to depart VFR to one destination then flies to random waypoints.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.