Date: 201606
Local time of day: 1201-1800
Location: TUS.Tower, AZ
Flight conditions: VMC
Light: Daylight
Aircraft: Small Aircraft; High Wing; 1 Eng; Fixed Gear
Operator: Personal
Operating under: Part 91
Flight plan: VFR
Mission: Personal
Flight phase: Final Approach
Airspace: Class C TUS
ATC / advisory: Tower TUS
Reporter organization: Government
Reporter function: Supervisor / CIC; Ground
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Workload; Situational Awareness; Communication Breakdown; Distraction
Second reporter function: Local
Anomaly: ATC Issue All Types; Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Executed Go Around / Missed Approach
Contributing factors: Procedure; Human Factors; Staffing
Primary problem: Staffing

Narrative: I had just taken possession of Ground Control with flight data/clearance delivery combined because the FD/CD Controller was on his way home sick. A rescue vehicle called to relocate from the base of the tower over to the west end of the airport. Initially; I told the vehicle to hold short of the crossing runway (Runway 21) as I was busy helping to sign out the controller going home. Runway 21 being active had already been coordinated with me for an inbound landing. After working on the computer I turned to notice the vehicles approaching Runway 21 at Taxiway alpha and forgot why I was holding them there; and told them to cross the runway. I saw that we had an aircraft on final and instructed local to send them around while the vehicles were crossing. He did so and the aircraft circled for Runway 21 and landed safely.I should have been more aware that I stopped that aircraft for a reason. Had I moved back to my working position at ground; I would have seen why and used the placards and info written down in front of me as a reminder to leave them where they were (already holding short of the runway for an inbound).The shift was very short-staffed and I was being used for staffing and relief to support the operation. I was not anticipating losing another body to sick leave on an already short shift.


Second narrative: I called GC to call RWY 3/21 HOT per the TUS SOP. GC was in the middle of a clearance read back from an airliner. I looked over and quietly stated 'Runway 21 HOT' as the pilot was reading his clearance back to GC; GC read back '21 HOT'. Aircraft X was cleared to land on RWY 21 and very short final (2 minutes later) I saw 3 fire trucks crossing RWY 21 at Taxiway A. GC (the supervisor on duty as well) stated out loud 'Send that guy around' and I complied with the instruction; sending him around. Aircraft X landed without incident after one trip around the pattern.I won't state '21 HOT' when someone is listening to a clearance. I will watch vehicles even when not on my frequency; workload permitting.


Synopsis: TUS Ground and Local Controller reported a runway incursion due to Ground Control conducting other  functions as the FLM.  Ground Control crossed vehicles with aircraft on short final due to being distracted.