Date: 201907
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Distraction
Second reporter function: Captain; Pilot Not Flying
Anomaly: Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Runway
Detector: Person Flight Crew
When detected: Taxi
Result: Flight Crew Rejected Takeoff
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: We were cleared for departure on Runway XXL by Tower. The Captain lined the aircraft up and passed control of the aircraft to me; the Pilot Flying. I started advancing the thrust levers up and at the same time I noticed a (other carrier) aircraft; which previously landed on Runway XXR; about 3000' or 4000' from us; not holding short of Runway XXL as instructed. (Other carrier) aircraft subsequently entered the runway. I still had my hand on the thrust levers. I immediately brought the thrust to idle and gently got on the brakes. We advised ATC that we were rejecting the takeoff due to the (other carrier) aircraft entering the runway. The Captain took control of aircraft and I assumed PM [Pilot Monitoring] duties. We taxied off the runway; ran the appropriate checklists and determined the brakes were not too hot for another departure. The Captain spoke with the guests then we departed. This took maybe 10 to 15 minutes. We reviewed our fuel on board and both agreed we were legal for departure.


Second narrative: We approached the intersection of Taxiway 'C' and 'B1' at ZZZ single engine; having anticipated a delay. We were surprised to find out from Tower there was no delay; and we immediately started our #1 engine. After finishing the Before Takeoff Checklist; we were cleared for takeoff on Runway XXL. The time was XA: 55:06 Z. We taxied slowly to ensure we would have our two-minute warm-up time and aligned the aircraft for takeoff. I transferred control to First Officer; and the engines started to spool up as he advanced the throttles in anticipation of selecting TO/GA. The time was XA: 56:30 Z. I momentarily looked down to adjust the radar; and before I looked up; F/O had exclaimed that something was wrong and started easing the throttles back to idle. At that time he had not yet pushed TO/GA; the airspeed indicator had not left the 45-knot rest position; and I had not yet taken the throttles back after what normally would have been 'set takeoff thrust' call. When I looked up; the red stop bars had illuminated and a (other carrier) aircraft was crossing XXL downfield at 'Y.' I queried the Tower. They cancelled our takeoff clearance and had us exit the runway at 'J.' I took control of the aircraft and slowly taxied off the runway. Tower apologized and assured us that we did in fact have takeoff clearance and that (other carrier) had been instructed to hold short. We referenced the QRH to review the Rejected Takeoff considerations on page X.Y and completed a performance brake energy calculation. We were considerably less than 9.8 MFP; as we had selected 50-knots--this was higher than our actual reject speed we would later realize. No delay was required. We talked to the passengers; relayed our readiness to Tower and had an uneventful takeoff at XA: 11 Z. F/O's [First Officer's] decision to abort was correct. I had not yet taken the throttles; the danger of continuing was obvious; and by the time I saw the (other carrier) aircraft crossing down field; a few critical seconds had passed--he noticed the hazard first. In all reality; we were at a mere taxi speed (autobrakes had not engaged); and it felt that way to the Flight Attendants and passengers.


Synopsis: Flight Crew reported a rejected takeoff due to runway incursion.