Date: 202102
Local time of day: 1801-2400
Location: SCK.Airport, CA
Flight conditions: VMC
Weather elements / visibility: 10
Light: Night
Aircraft: Small Aircraft
Operator: Personal
Operating under: Part 91
Flight plan: VFR
Mission: Personal
Flight phase: Takeoff / Launch
Airspace: Class G ZOA
ATC / advisory: UNICOM SCK
Reporter organization: Personal
Reporter function: Single Pilot
Reporter qualification: Flight Crew Commercial; Flight Crew Instrument
Human factors: Communication Breakdown; Situational Awareness
Anomaly: Conflict Ground Conflict; Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Vehicle; Ground Incursion Runway
Detector: Person Flight Crew
Result: Flight Crew Took Evasive Action
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: I was holding short of Runway 29R on Taxiway B2 at Stockton (SCK) in preparation for a VFR departure en route to ZZZ; waiting for a [Company] heavy aircraft to land and clear the runway. The prevailing conditions were night VFR; with unlimited visibility; clear skies; and minimal wind. Stockton Tower was closed; and traffic was coordinating via CTAF. After the heavy aircraft landed and cleared; I made my CTAF call indicating that I was taking Runway 29R for departure. The heavy aircraft crew acknowledged my transmission and noted that they were clear of all runways. While beginning my takeoff roll; a ground vehicle; self-identified as a tug; made a radio call on CTAF that they were crossing Runways 29L/29R en route to the cargo ramp. This was the first call the tug made on CTAF. I made another radio call noting that I was in my takeoff roll; and began visually searching for the tug. I reduced engine power to idle; and applied heavy braking. At that time I saw the tug's anti-collision lights cross in front of my aircraft. I stopped on the runway and made an additional radio call noting that I was aborting takeoff and returning to RWY (Runway) 29R. At no point did the tug acknowledge any of these radio calls or change behavior. I returned to RWY 29R and made an otherwise uneventful departure.Primary cause of the problem: runway incursion by airport tug vehicle that was broadcasting on; but possibly not monitoring; the CTAF frequency.Proximate causes of the problem: airport ops vehicles likely unused to operating on CTAF after-hours at normally tower-controlled airport. Night conditions may have made it difficult for the ops vehicle to see my aircraft on the runway; and made it more difficult for me to see the ops vehicle. Complacency: SCK is a cargo airport; and extremely quiet at night. It's possible that the ops vehicle crew was accustomed to only seeing large cargo aircraft operating at SCK at night; and so my comparatively smaller (and unscheduled) aircraft may have not been noticed/ignored. Finally; the airport operations staff may not have been aware that entering a runway - even several thousand feet down the runway from a takeoff aircraft - is still prohibited.Preventative measures: training for airport ops crews on proper radio use; importance of clearing runways prior to crossing; and runway incursion avoidance best-practices.




Synopsis: Pilot reported on takeoff roll; a ground tug crossed the runway in use; resulted in aborted takeoff with evasive action.