FSX multiplayer cannot share built-in ATC or AI traffic over a LAN. See what synchronises, why PCs drift, and which alternatives work.
No. In Microsoft Flight Simulator X (FSX) and FSX: Steam Edition, native multiplayer shares human-controlled aircraft and supported shared-cockpit data, not one master copy of automated ATC or AI traffic. A LAN lowers network delay, but every ATC computer does not receive a synchronised traffic simulation from the host.
What does FSX multiplayer synchronise over a LAN?
It synchronises the human participants and selected session data, not the host computer's complete offline simulation.
| Element | Native multiplayer behaviour |
|---|---|
| Human-controlled aircraft | Position, attitude and other multiplayer data are transmitted. Missing aircraft models may appear as substituted or generic aircraft. |
| Shared-cockpit controls | Supported controls and instruments can be synchronised when the session and aircraft support shared cockpit. |
| Built-in automated ATC | No common ATC state is distributed. Automated clearances, radio calls and ATC menus are not shared between the computers. |
| Stock AI traffic | AI aircraft are not distributed as common multiplayer objects. Traffic generated or injected locally remains local unless separate software explicitly networks it. |
| Human Tower Controller | A controller can direct participating human pilots where the installed FSX edition and session support that role. This does not add shared automated ATC or AI aircraft. |
A physical LAN changes the connection route, not the data FSX transmits. Original boxed FSX uses its legacy local-network facilities, while FSX: Steam Edition uses Steam's multiplayer layer even when both PCs share a router. Our explanation of how boxed FSX and Steam Edition multiplayer differ covers the connection options in more detail.
Does FSX shared cockpit also share ATC and AI?
No. FSX shared cockpit synchronises one aircraft's supported cockpit state between a pilot and co-pilot; it does not merge the two computers' surrounding traffic or ATC simulation.
Complex add-on aircraft may use custom systems which FSX's shared-cockpit code cannot fully synchronise. If two people want to operate the same aeroplane, follow our FSX shared-cockpit setup and compatibility guidance, but treat ATC and traffic as separate issues.
Why are AI traffic and built-in ATC not shared?
AI traffic and automated ATC belong to FSX's local simulation engine rather than its list of networked player aircraft.
FSX does not send every AI aircraft's schedule, taxi state, runway reservation, clearance queue and radio exchange to the other machines. In a standard native multiplayer session, the offline Free Flight combination of stock AI and automated ATC is therefore not available as one shared system.
If an add-on or unusual configuration injects local traffic during a session, that traffic still exists only on that computer unless the injector was specifically designed for network synchronisation. Tuning both pilots to the same frequency does not copy an ATC clearance or radio call from one PC to the other.
What supplies shared ATC in an FSX LAN session?
A human participant using the Tower Controller role supplies shared instructions to the human pilots, where that multiplayer feature is available.
The role was not included with every original boxed FSX edition, so the controller computer must have an edition that supports it. It provides a common human voice or text service, but the controller does not become an authoritative server for stock AI traffic.
Can two ATC computers use one traffic simulation?
No, not through native FSX multiplayer. A second tower or ATC computer does not inherit the host's local AI aircraft, automated clearances or complete traffic picture.
Creating a genuinely common picture requires software explicitly designed around a central traffic source and networked clients. Before relying on such software, verify support for the exact FSX edition, operating system, aircraft models, airport scenery and firewall arrangement. Matching installations alone cannot add a network protocol that FSX does not have.
Can identical files make AI traffic match on both computers?
Only approximately, and only when both computers are independently generating or injecting local AI traffic.
- Match the traffic schedules: install the same traffic BGL files on both machines. These are often placed under
Scenery\World\scenery, although an add-on can use another active scenery folder. - Install every required aircraft: both installations need the same AI models and liveries under
SimObjects\Airplanes. Copying only the schedule is a common cause of missing traffic. - Use identical airport data: differing airport facility or AFCAD files can change gates, parking sizes, taxi routes and available runways.
- Match the simulation conditions: use the same date, time, weather, wind and airline and general-aviation traffic settings.
- Keep the clocks together: load at the same time and avoid pausing or using time acceleration on only one computer.
Even then, differences in loading time, available parking and local processing can make aircraft spawn, taxi or disappear at different moments. Our advice on configuring local AI schedules, models and traffic density can help both installations use the same source material, but it cannot turn them into one authoritative traffic simulation.
Which setup should you choose?
Choose the setup according to what must be shared: the aircraft, the controller or the entire AI traffic state.
| What you need | Best fit | Main limitation |
|---|---|---|
| Human pilots visible to one another | Native FSX multiplayer | Automated ATC and AI traffic are not shared. |
| Two people operating one aircraft | Native shared cockpit | Aircraft compatibility varies, especially with custom systems. |
| Common ATC for a private group | Human Tower Controller role | Controls human participants, not a synchronised stock AI world. |
| Shared online controllers and human traffic | VATSIM through vPilot | Controller coverage is provided by people and is not continuous; it is not scheduled AI traffic. |
| Identical scheduled AI on every screen | A compatible network-aware traffic system | Native FSX multiplayer, matching sliders and copied BGL files cannot provide this by themselves. |
For network ATC, vPilot is used from a normal FSX flight rather than by joining a native FSX multiplayer session at the same time. It displays connected network pilots using model matching, while controllers and pilots work from the same online traffic picture. Our FSX and VATSIM connection instructions explain the setup. Disable local FSX AI in that arrangement so it does not create traffic which controllers and other pilots cannot see.
If the human-controlled aircraft themselves are missing, treat that as a multiplayer connection, session or model-matching fault. If only automated ATC and AI are absent, that is the expected native limitation rather than evidence that the LAN has failed.