Date: 202004
Local time of day: 1801-2400
Location: PHL.Airport, PA
Flight conditions: VMC
Light: Dusk
Aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Landing
ATC / advisory: Tower PHL
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Communication Breakdown; Time Pressure
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Conflict Ground Conflict; Critical; Ground Incursion Runway
Detector: Person Flight Crew
When detected: Other Landing
Result: Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: I was CA (Captain) flying [the] visual approach to Runway 27R tracking ILS 27R. Daylight/Dusk VMC. We were cleared to land and no traffic in sight as previous landing traffic had cleared. After landing in the rollout phase Tower said go around! My initial thought was that [there was] someone landing behind us and was too close. I then happened to look down the runway and see an aircraft taxi onto the runway further down about 2000 ft. I was in reverse with full flaps and spoilers at about 80 kts. when my First Officer stated I think Tower said go around. Almost immediately I keyed the mic and said we have November (N) Taxiway; just before my planned exit K4. As I exited at November; I saw the aircraft continue to slowly cross 27R from the vicinity of Tango Taxiway.Tower instructed us to monitor a frequency for a phone number to call after arrival at [the] gate. The gravity of the situation did not appear evident until after both myself and my First Officer debriefed the situation and agreed that we were cleared to land and there was no traffic in sight until after landing. We both agreed that we could not 'go around' from a landing configuration with full flaps; in reverse; and spoilers deployed after landing.This safety error/event happened either due to an excursion by another aircraft onto the active runway by mistake or misunderstood ATC clearance. We were cleared to land and [with] no traffic visible on [the] runway; we landed normally. While we were in the rollout decelerating; tower either by mistake or confusion told us to go around with traffic on the runway less than 2000 ft. ahead. This runway excursion event happened by error. I believe either the flight misunderstood hold short or was not familiar with the taxiway configuration. Or; ATC gave a clearance that was incorrect and or got distracted with the taxiing aircraft movement. In any case; I saw the aircraft on the runway in time to slow and exit early. There was no way to do a go around from full landing configuration while in reverse; slowing; with full flaps; spoilers and on brakes.The remaining distance 2000 ft. or less would not be enough to reconfigure to a take off condition. If so; there is no way to get safely airborne and clear intruder traffic in that distance. We did the safest action which was to stop and clear the runway.


Second narrative: I was the monitoring pilot during landing. Just after landing; spoilers were deployed; reverse thrust was being used and the aircraft was slowing through about 80 to 90 kts. We heard the Tower say to go around. I wasn't sure he was talking to us; but I looked up and saw an aircraft crossing the far end of the runway. Trying to execute a go around at the current energy state of the aircraft and trying to clear the other aircraft would've been very hazardous. I called the Tower and said that we were already braking. The Captain continued to slow the aircraft and we turned off on the taxiway towards the terminal. Except for an aircraft crossing the far end of the runway; the landing was completely normal; and we did not use any type of evasive maneuvers.


Synopsis: Flight crew reported that as they were landing Tower told them to go around for an aircraft crossing the runway but the crew could not comply as they were already configured on their landing roll.