Learn how to install and use SimConnect with FSX: Steam Edition, add legacy runtimes, connect tools and fix common connection failures.
FSX: Steam Edition already includes SimConnect; you do not install a separate program to enable it. For older add-ons, run the required legacy SimConnect MSI from the simulator’s SDK folder, load a flight, then start the add-on. Local connections normally need no SimConnect configuration files.
Is SimConnect already installed in FSX: Steam Edition?
Yes, the simulator’s native SimConnect components are installed with FSX: Steam Edition. SimConnect is an application interface, not a standalone utility, so it has no desktop shortcut, control panel or dedicated menu inside FSX.
External programs use SimConnect to read aircraft data and send commands. In-process DLL add-ons may load through dll.xml. Neither type is guaranteed to appear under FSX’s Add-ons menu, and SimConnect does not require FSUIPC unless the particular utility explicitly asks for both.
How do I install the legacy SimConnect runtimes?
Install the legacy clients when an older aircraft, utility or installer reports that SimConnect is missing or cannot initialise. FSX supports these clients side by side, because add-ons can request different SimConnect generations.
- Close FSX and the add-on. Also allow any failed installer process to finish before continuing.
- Open the FSX installation folder. In Steam, use the option to browse the game’s installed files rather than assuming it is on the
C:drive. - Open the legacy interfaces folder:
SDK\Core Utilities Kit\SimConnect SDK\LegacyInterfaces. - Follow the add-on’s requirement if it names a package. The usual subfolders are
FSX-RTM,FSX-SP1andFSX-XPACK, each containing aSimConnect.msiinstaller. - If no version is specified, install all three legacy clients in RTM, SP1 and XPACK order. They are designed to coexist; one does not simply replace the others.
- Respond appropriately if an MSI detects an existing installation. An offer to repair or remove the package means that client is already registered. Choose Repair only when diagnosing a fault; otherwise cancel it.
- Restart Windows if an installer requests it, then test the add-on with a flight fully loaded.
If the SDK or LegacyInterfaces folder is absent, first run Steam’s file-verification function. Our guide to finding and repairing the FSX SDK installation explains the Steam and boxed-edition differences.
Do not download a loose SimConnect.dll and copy it into the FSX root folder. SimConnect uses registered side-by-side assemblies, and an arbitrary DLL can introduce the wrong interface version without repairing the missing runtime.
How do I use SimConnect with an FSX add-on?
A local SimConnect add-on should connect automatically once FSX has loaded into an active flight. There is no FSX setting that must be switched on.
- Start Steam and FSX: Steam Edition.
- Load an aircraft at an airport and wait until the cockpit is usable. Some clients cannot connect from the opening menu.
- Start the external utility unless its instructions require it to launch first.
- Keep both programs at the same privilege level. Running both normally is preferable; avoid running only one as administrator.
- Confirm that the utility is configured for FSX or SimConnect, rather than a different simulator or an FSUIPC-only connection.
A local connection usually needs neither SimConnect.cfg nor a custom SimConnect.xml. Creating those files unnecessarily is a mistake we see often: a wrong protocol, address or port can stop a connection that would otherwise work automatically. See our practical example of a local SimConnect connection for the normal startup and testing sequence.
Can SimConnect work across a network?
Yes, but a networked client requires deliberate server and client configuration. FSX’s SimConnect.xml defines the network protocol and listening port, while the remote computer’s SimConnect.cfg must use the same protocol, host address and port.
Allow the relevant programs through the Windows firewall and test on a private local network. The FSX profile folder may be named FSX or FSX-SE, depending on whether boxed FSX has also been installed, so do not edit the first similarly named folder you find. SimConnect should not be exposed directly to the public internet.
Why is my SimConnect add-on not connecting?
Most connection failures come from a missing legacy client, an add-on started before a flight loads, mismatched administrator privileges or unnecessary network configuration.
| Symptom | Likely cause and fix |
|---|---|
| “SimConnect not found” or a side-by-side error | Install or repair the legacy runtime requested by the add-on. If it does not specify one, install the RTM, SP1 and XPACK clients. |
| The utility waits indefinitely | Load completely into a flight, then restart the utility. Check that it is set to use FSX rather than another simulator. |
| It connects only when run as administrator | Close both programs and run them at the same privilege level. Check whether security software has blocked the client. |
| A local tool stopped working after configuration changes | Back up and remove manually created SimConnect configuration files, then retest using the default local connection. |
| A remote computer cannot connect | Match the address, protocol and port in the server and client files, then check the firewall and host IP address. |
| The MSI files or SDK folders are missing | Verify the FSX installation through Steam before attempting manual replacement. |
Multiple Microsoft Flight Simulator SimConnect Client entries in Windows’ installed-programs list are normal. Do not remove older entries merely because they look duplicated; an older add-on may depend on that exact client. For persistent installation, manifest or connection faults, follow our complete FSX SimConnect repair sequence.