Date: 201906
Local time of day: 1201-1800
Location: DVT.Airport, AZ
Aircraft: Bonanza 35
Flight phase: Taxi
Airspace: Class D DVT
ATC / advisory: Tower DVT
Second aircraft: PA-28 Cherokee/Archer/Dakota/Pillan/Warrior
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Distraction; Situational Awareness; Communication Breakdown
Anomaly: ATC Issue All Types; Conflict Ground Conflict; Critical; Ground Incursion Runway
Detector: Person Air Traffic Control
When detected: Taxi
Result: Air Traffic Control Separated Traffic
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: I cleared Aircraft Y for takeoff from C1 on Runway 7R. Meanwhile; training was in progress on Ground. I heard both the trainee and instructor yell 'No' at a higher level than normal which caught my attention for concern. I scanned down the runway at the aircraft waiting for a crossing and did not see them moving. As my scan got closer towards the approach end I heard them trying to transmit to Aircraft X to stop. At that moment I saw Aircraft X at C3 taxiing toward the runway while Aircraft Y was approaching the vicinity of the runway threshold marking; rolling at a rapid speed. I was not sure if Aircraft X was going to stop as at this point they were completely past the hold bars of taxiway C3. I knew that Aircraft Y had way too much speed to be able to stop and time was critical; so instead of taking canceling the takeoff clearance I used the time available to get their attention towards where Aircraft X was ahead and to their right so that they could maneuver out of the way if they were able. They were rolling too fast to stop; but not fast enough to rotate yet. I am not sure if Aircraft Y maneuvered to the left or not but they went past where Aircraft X was and departed without incident. Aircraft X stopped just short of the runway edge line; completely past the hold short markings on C3. After Aircraft Y was a safe distance upwind and at a safe altitude I turned them on course and they said that they had seen Aircraft X during their takeoff roll.Before this incident happened I had already put a Cessna in position at full length and there were 2 aircraft inbound. I sent the closer one around to prevent a flyover of the Cessna in position at full length as they could not depart with Aircraft X where they were. Aircraft X called me for departure clear of the runway edge marking; but completely past the C3 hold short lines. I verified with the pilot if they were still okay/comfortable to depart and they said affirmative. I advised them of the Cessna holding in position at full length and cleared them for takeoff. The Cessna departed afterwards without incident. Aircraft X remained in the pattern and landed without incident. The go around went around in the pattern and landed without incident.I am not sure what Ground said to Aircraft X that caused them to do that; but regardless Ground would never give a line up and wait or 'Position and Hold' instruction. It seems that at this airport; recently; I have noticed an increased number (than in the time that I have been here) of pilots taxiing onto the runway claiming that they thought Ground gave them permission to taxi onto the runway and wait for Tower to give them departure instructions. Perhaps some sort of emphasis in pilot training could be made to highlight the fact that Ground controllers do not have that type of authority regarding the runway and would never give such an instruction could help reduce the occurrence of these types of events.The event happened so quickly that not much time was given to be able to identify; react; and get a pilot response (either verbal or in the form of a pilot action) from the aircraft involved. I think Ground did a good job trying to stop Aircraft X even though they said they think their transmissions kept getting blocked; which is why it took Aircraft X so long to stop. The pilots in Aircraft Y did a good job hearing; understanding; and responding to my warnings about Aircraft X because a potential disaster was averted.




Synopsis: DVT Tower Controller reported an unsafe situation with a departure and an aircraft that needed to cross the runway.