Date: 201511
Local time of day: 1801-2400
Location: PRC.Tower, AZ
Flight conditions: VMC
Light: Night
Aircraft: Small Aircraft; High Wing; 1 Eng; Fixed Gear
Operator: Personal
Operating under: Part 91
Flight plan: VFR
Mission: Personal
Flight phase: Taxi
ATC / advisory: Ground PRC
Second aircraft: Small Aircraft; Low Wing; 1 Eng; Fixed Gear
Reporter organization: Government
Reporter function: Local
Human factors: Communication Breakdown; Distraction; Situational Awareness; Training / Qualification; Workload
Second reporter function: Ground
Anomaly: ATC Issue All Types; Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Detector: Person Air Traffic Control
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew FLC complied w / Automation / Advisory
Contributing factors: ATC Equipment / Nav Facility / Buildings; Airport; Environment - Non Weather Related; Human Factors; Procedure; Staffing
Primary problem: Airport

Narrative: I was training on Ground Control/Flight Data. The developmental issued a taxi route to Aircraft X that included an inactive runway crossing and a runway hold short instruction of the active runway. Aircraft X read back the clearance correctly. The developmental was falling behind with a high volume of work and frequency congestion from multiple simultaneous calls. To my right; the Local 1 position had just finished a position relief briefing and another Developmental was plugged in receiving a briefing from the Local 1 OJT (On Job Training) Instructor. The Controller-in-Charge position was also conducting a position relief briefing to my left. Behind me was the Local 2 controller and other controllers who had just been relieved; exiting the tower cab; and an intern who was plugged in monitoring. The tower cab was crowded with controllers all standing shoulder to shoulder and little ability to move.I recognized my Developmental was falling too far behind and began to prepare to take over the frequency. My developmental standing was initially blocking my view of the taxiways intersection. Once I could re-position myself to gain a view of Aircraft X I observed Aircraft X on the active Runway at an intersection of another runway. My developmental was looking at another aircraft calling from a ramp and transmitting to them when I keyed over him to tell Aircraft X to exit the runway at the closest and quickest way off the active runway. Aircraft X had crossed approximately 750-1000 feet in front of another aircraft on the same runway at taxi speed.Multiple factors led to this runway incursion unfolding beginning with the reason why Aircraft X requested taxi. Aircraft X is part of a [company] located [on the East side of the airport]. This [company's] fuel tank is located on the Northwest corner of the airport which requires two runway crossings each way to get from their ramp to their fuel tank in order to refuel aircraft. It is quite common to have these aircraft request taxi from their ramp to refuel; and then back to the ramp to park during peak hours of traffic volume. We have worked around the needs of the [company]. Educating the [company] of the hazards this operation presents; especially during peak hours; and familiarization with the airport layout.A crowded Tower cab with a lot of activity changing simultaneously combined with multiple obstructions to view to all controllers; including myself and the Local 1 Controller; was also a contributing factor. Better pre-planning of position relief briefings and limiting of the number of people in the cab to aid in mobility and visibility.The taxiway intersection where the incursion occurred is a known hotspot due to taxiway complexity which also may have played a part in the pilot's interpretation of the instruction. Aircraft X had encroached upon the runways intersection when I instructed them to exit; it was too late to stop Aircraft X short.


Second narrative: At the time of the event I was training on ground control combined with flight data and clearance delivery.  Aircraft X; called for taxi. I gave the taxi instruction to Aircraft X. Aircraft X read back the taxi instruction completely and correctly. After hearing the correct read back; I focused my attention to the other traffic building at the time. Approximately one minute later; my trainer keyed up and told Aircraft X to turn onto the taxiway. Unbeknownst to us; Aircraft X made a wrong turn onto the taxiway and crossed the runway an estimated 750 feet in front of Aircraft Y who had just landed and was in a landing roll. Aircraft X was not observed by ATC until he had already entered the active Runway and was at the intersection of two intersecting runways. At the time of the event; training was occurring on the Local 1 position and a position relief briefing/transfer of control to the Local 1 trainee was in progress. I was also standing in my position at the ground control station; which further blocked the view of the runway for the local controller and his trainee. The Controller-in-Charge had recently been switched and the Controller-in-Charge was focused on the desk duties at the time of the incursion. The incursion did happen at a hot spot on an exit only taxiway so additional signage may help play a role in helping to prevent an event like this from happening again. The runway configuration makes it difficult for the local controller to fully scan the runway as the ground control position is in the line of sight. Had I been sitting down and not standing; the local controller may have been able to see the incursion about to happen before it was too late.


Synopsis: Two air traffic controllers reported on a runway incursion that took place while conducting on-the-job training. The aircraft was issued taxi instructions to hold short of an active runway. The student pilot read back the instructions correctly yet taxied on to the active runway as another aircraft was landing. A shift change was occurring in the Tower and was crowded with people obscuring the controllers' views of the airport.