Air Traffic Control Fully Certified
Situational Awareness; Training / Qualification
ATC Issue All Types; Conflict Ground Conflict; Critical; Deviation / Discrepancy - Procedural Clearance
Human Factors
Aircraft X landed Runway 28R and slowed enough to make [the] turn off on Runway 32. My Trainee instructed pilot to turn right on Runway 32. We observed Aircraft X begin to turn; but then return to centerline and continued down runway. Once trainee saw Aircraft X begin a turn; he quickly cleared Aircraft Y for takeoff before verifying Aircraft X had actually exited the runway. Before I could key up to cancel the takeoff clearance; Aircraft Y rejected the clearance saying he saw the other aircraft still on the runway. I told Aircraft Y to cancel takeoff clearance and hold position. Aircraft X then missed the next turnoff and moved very slowly down the runway. Aircraft X asked us which exit he was supposed to make. As this was happening; [the] Trainee decided the next arrival was too close to get Aircraft Y airborne; [and] he instructed Aircraft X to turn right and exit runway at C12. Aircraft X was instructed to exit at C5 and contact Ground. Aircraft Y was not exiting the runway quickly enough; so Trainee told Aircraft Z to go-around. Trainers and trainees must do a better job of scanning runways and verifying arrivals have exited prior to issuing takeoff clearance to subsequent aircraft.
PBI Tower Controller/Instructor reported a runway incursion involving an arrival not exiting the runway quick enough; a departure cleared for takeoff; and an arrival having to be sent around.