FSX multiplayer cannot natively share ATC or AI traffic over a LAN. See what synchronises, why matching traffic files falls short, and what works.
No. FSX and FSX: Steam Edition multiplayer synchronise participating users’ aircraft, not the simulator’s built-in ATC state or locally generated AI traffic. On a LAN, each PC runs its own ATC and AI simulation. Matching files and settings can make traffic look similar, but it does not create one shared traffic world.
What does FSX multiplayer synchronise over a LAN?
FSX multiplayer sends player-related session data; it does not make the host authoritative for every object in the simulation.
| Element | Native multiplayer result |
|---|---|
| Other players’ aircraft | Synchronised, although a missing aircraft model may be replaced with a fallback model or livery. |
| Shared-cockpit controls | Synchronised when shared cockpit is enabled and the aircraft supports it properly. |
| Automated FSX ATC | Not shared; each computer maintains its own clearances, radio calls and ATC menus. |
| Airline and general-aviation AI | Not shared; where AI is running, each computer generates it locally. |
| Human Tower Controller role | Can direct participating human pilots in supported sessions, but does not synchronise automated ATC or local AI aircraft. |
A physical LAN can reduce latency, but it does not expand the types of data FSX transmits. Boxed FSX and Steam Edition also use different connection systems; our explanation of boxed FSX LAN play and Steam Edition networking covers that distinction. The ATC and AI limitation is the same in both editions.
Why do ATC and AI differ between the two PCs?
Each computer independently manages flight plans, parking allocation, runway selection, traffic spawning and the ATC queue. A clearance accepted on one PC is not copied to the other PC, even when both pilots are tuned to the same frequency.
Differences in airport scenery, traffic density, weather, local simulation time, pauses and time acceleration can quickly produce different results. One pilot may hear an AI aircraft receive take-off clearance while the second pilot neither sees nor hears that aircraft.
The built-in Tower Controller role is the native option for common human ATC where the edition and session support it. It lets one participant direct the human pilots, but it does not turn one PC’s scheduled AI aircraft into shared network objects.
Can identical traffic files make both PCs match?
Identical installations can produce a convincing approximation, but they cannot guarantee identical aircraft positions or ATC decisions.
- Install the same schedules and models: both computers need matching traffic BGL files and the aircraft models referenced by those schedules. Our guide to locating FSX AI traffic files helps identify what must match.
- Match the airport data: use the same scenery and airport layout files so parking positions, taxiways and runway availability agree.
- Match the simulation state: set the same date, local time, traffic sliders, weather and wind.
- Start together: load both flights at the same time and avoid independent pauses or time acceleration.
A mistake we see constantly is copying the traffic schedule without installing its required aircraft models and liveries. That can leave one computer with missing or substituted traffic. Even a perfectly matched setup remains two separate simulations and will eventually drift.
What are the practical ways to share ATC and traffic?
Use a human controller or a network-aware external system when every pilot must work from one traffic and ATC picture.
- Native human ATC: choose the Tower Controller role when the session consists mainly of human pilots. It provides common instructions without attempting to synchronise scheduled AI.
- Shared online ATC: VATSIM with vPilot supplies a common controller environment and traffic formed by connected human pilots. Our FSX and VATSIM connection instructions explain the setup. Local FSX AI is normally disabled to prevent unrelated or duplicate traffic.
- Dedicated traffic synchronisation software: choose a compatible network-aware traffic injector if scheduled AI must occupy corresponding positions on every PC. Verify support for each FSX edition, model mapping, scenery compatibility and required firewall ports; native multiplayer cannot provide this function by itself.
If the human-controlled aircraft do not appear on each other’s screens, that is a separate networking fault rather than an AI limitation. Work through our FSX multiplayer connection checks before changing traffic files or ATC settings.