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The multiplayer feature of FlightGear makes it possible to see other pilots and vice-versa. This makes it possible to fly in formation, perform mid-air refueling with tankers controlled by real people or contact real air traffic controllers to ask for guidance.

Multiplayer may cause extreme framerate drops during the loading of aircraft models, especially heavy models such as the Boeing 777 or Airbus A320neo. It is suggested to fly in locations other than the default San Francisco International Airport, as there are often lots of pilots in the area who are often new, and do not follow ATC, or respect traffic.


  • Callsigns can be a maximum of seven characters.
  • You might want to check the Known issues section.

Connecting to Multiplayer

Built-in launcher and in-sim dialog

Multiplayer settings dialog

The easiest way to get online is to use the built-in launcher or the in-sim Multiplayer dialog. All you need to do is enter a callsign and select a server from the menu. Press Connect to go online.

Using FGRun

From the main page

Multiplayer settings in FGRun
  1. Select your aircraft and starting airport as normal in FGRun.
  2. On the last screen, tick the "Multiplayer" box. Also make sure that the "AI models" box is checked or you will not be able to see the other pilots' aircraft.
  3. Enter the …
    • Callsign of your choice.
    • Hostname: Enter (with XX being the server number).
    • In/Out: Set both ports to 5000.
  4. Click Run to start FlightGear.

To confirm that it's working, you can go to the multiplayer map at (in Hong Kong). Once FlightGear has started, you will notice chat messages that say "Hello" indicating pilots that are online. They will also pop up when a pilot joins the MP network. You can change this message by add command line option, e.g.:

 --prop:string:/sim/multiplay/chat="Greetings pilots"

You may wish to use a different server, especially one closer to you.

From Network Settings

The Network tab of the Advanced Options dialog in FGRun (in FlightGear 3.2.0).

You can also change multiplayer settings in the Network tab of FGRun's Advanced Options.

  1. On the last page, click Advanced.
  2. Click Network in the left column.
  3. In the Multiplayer Options area …
    • Type your desired callsign into the box.
    • Set the parameters for the two other boxes; see below for correct syntax.
    • Click OK, then run FlightGear.

Using multiplayer from the command line

When running FlightGear from the command line, you can specify multiplayer settings. The two arguments are as follows:


Obviously, --callsign can be anything you wish but it must be limited to 7 (seven) characters in length counting any dashes. If your callsign is too long, it will be cut off in the various displays where it is shown. Generally speaking, callsigns are of the form X-XXXXX. Check this page to see whether your callsign is already in use or not. Do not pick a callsign that is already used, as that will create problems! Please don't leave your callsign as "CALLSIG".

There are four arguments to --multiplay:

Either in or out. in tells FlightGear to listen to packets of data coming in through the specified port. out tells FlightGear to send data out through the port.
IP address of network interface being used by FlightGear. If left blank, FlightGear will listen to all network interfaces. If direction is set to in, FlightGear will listen to only this IP address.
Port that data is either being sent or received through. Usually set to 5000 and above.

Advanced usage of multiplayer

Local setup for testing

It is possible to set up a local multiplayer network between two FlightGear instances without using a multiplayer server. All you need to do is map each I/O port of one instance to the corresponding port(s) of the other instance:

Cquote1.png A socket connection requires not only an IP address, but also a port number for each side of the link - imagine a port number like a "mailbox" sitting at the address. This mailbox is used by the communicating processes to send out and receive "messages". Different processes (even when possibly identical programs) will need to use different port numbers when running. Because open ports (=mailboxes) cannot be shared.

Thus, you need to modify the client-side port settings for each additional instance that you are running on the same machine, and map the output port of one instance to the input port of the other instance (and vice versa).


Command line parameters for the first instance:

--multiplay=out,10,,5000 --multiplay=in,10,,5001 --callsign=Test1

Command line parameters for the second instance:

--multiplay=out,10,,5001 --multiplay=in,10,,5000 --callsign=Test2

You can use this kind of setup to test multiplayer related features or troubleshoot multiplayer related bug reports that may be otherwise hard to reproduce over MP. As you can't access the configuration of other people's FlightGear, this technique allows you to have complete control over FlightGear's settings.

Screenshot demonstrating a "peer-to-peer" setup between two FlightGear instances running on the same machine via localhost ( without any multiplayer server.

You can add an arbitrary number of channels to mirror your flight onto other servers, e.g. to a private fgms (FlightGear Multiplayer Server) using


Additionally, the in argument above tells FG to listen only on the loopback/local interface - it will not receive packets arriving on the other network interface(s). If you want to also bind to other interfaces, just omit the IP address by using


Check this page to see whether your callsign is already in use or not. Do not pick a callsign that is already used, as that will create problems!

Now, going more slowly for those who are completely lost...

Note  This section may contain out of date or inaccurate information.

This section ought to be unnecessary now with recent versions of the FG server. If you have problems though, it won't hurt to follow through.

First of all, you need to know the IP address of the network interface you'll be using for multiplayer FG.

If your Internet connection is via an ADSL modem that plugs directly into your computer, you should be able to find your IP address by visiting

Note  Your ISP might not give you the same IP address each time.

If your connection is via an Ethernet connector or by a wireless link.

  • Linux: Log in as root and run ifconfig in the terminal. In the text that is returned, you should to look for an interface name such as eth0 or wlan0. Finally, look in the text below the interface name for inet addr:ip.address. For example, this should read something like inet addr:
  • Windows:
    • Windows XP or later: Start Command Prompt and ipconfig into the terminal. Write the IP address down.
    • Windows 98, click start, run, and type "winipcfg" to get information about your IP address.

Now, all that remains is to configure your router to forward UDP port 5000 to the IP address you've just found. This is not something that can be described in step-by-step detail, because each manufacturer's configuration interfaces differ greatly. Some tips are given here – if you get stuck, ask nicely on the FlightGear IRC channel for help (details on the FlightGear website).

You should know how to log on to your router's configuration page, usually via a web browser. You are looking for settings pertaining to "port forwarding," "virtual server," "Forwarding Rules," or similar. When you have found the relevant settings, you need to add a rule that forwards port 5000 to the IP address you discovered earlier. If there is a choice given, ensure it is UDP ports that are forwarded. If there is no choice, you may assume that both TCP and UDP are being forwarded. Save your configuration, and most routers will probably then need to be rebooted to apply the changes.

Note  BSD users: If you are using a ADSL modem, you might have to put the port forward command into the ppp.conf file rather than firewall. This is because the firewall script will only run each time the machine is booted rather than the ppp line coming back online.

Finally, start FG using the command line given right at the start (if you're using the Windows launcher you will find entry boxes for Multiplayer arguments – insert the relevant details there). You will end up with something like this:

<other arguments> --callsign=test --multiplay=in,10,,5000 --multiplay=out,10,,5000 --airport=KSFO --runway=28R --aircraft=hunter

Choose your own callsign, but check this page first to see whether your desired callsign is already in use or not. Do not pick a callsign that is already used, as that will create problems!

Once you have started FG, you should, if others are flying, see messages in the terminal from which FG was started, similar to the following;

Initialising john51a using 'Aircraft/ufo/Models/ufo.xml'  
FGMultiplayRxMgr::ProcessRxData - Add new player. IP:,  
Call: john51a,model: Aircraft/ufo/Models/ufo.xml 

You MUST give your local, behind-the-router IP address for multiplayer to work. Trust me on this one!

You should check that your firewall is not causing problems - either turn it off temporarily or add an exception to allow incoming connections on port 5000.

If it's still just not working for you, ask nicely on the IRC channel or the forum This is a link to the FlightGear forum. and someone should be able to assist.

Multiple connections per computer

It is possible to run multiple FlightGear instances on a single computer and connect them all to the multiplayer network. However, this requires some extras to keep in mind:

  1. Both instances use the same out port.
  2. One instance uses in port 5001, the other port 5002.
  3. Both instances have unique callsigns.

Optional collision detection in multiplayer

A patch has been added to FlightGear (since Version 3.5) to allow optional collision detection in multiplayer. To enable collision detection, start FlightGear with:


Those who are able to patch FGData themselves, can download mp-hot-fgdata.patch, which adds a checkbox to the Multiplayer Settings dialog to enable or disable the collision detection at runtime.

Multiplayer chat

1rightarrow.png See Chat Menu for the main article about this subject.

To chat with other pilots, go to the Multiplayer menu and select Chat Menu at the bottom of the menu. Note that the other pilots may not have their chat box open nor chat messages enabled, so they may not see your messages.

The shortcut for chatting is - (hyphen). This will bring up some text in the upper-left of the FlightGear window. By pressing the corresponding number keys, you can send pre-made messages. Pressing 1 will let you type in a custom message, which you can send by pressing enter. By default, other people's messages are displayed at the top of FlightGear's window for a few seconds, but it will appear for a much longer time in the window at Network > Chat. So if you think you have missed anything, go check there.

Dealing with abusive behavior

Should you become victim of abusive or annoying behavior by any pilot, you have option to ignore him or her. To activate the ignore function open the Multiplayer > Pilot list dialog and click the ignore button next to the pilot's callsign. This will prevent chat messages from the ignored pilot appearing and prevent his aircraft from appearing.

Multiplayer map

MPMap screenshot

1rightarrow.png See MPMap for the main article about this subject.

There is a very nice online map which displays the location of online pilots at mpmap02. You will also find this useful to check that you are successfully connecting to the server, as well as looking up navaids, waypoints, airports, frequencies, weather, and more!


The multiplayer servers are interconnected. With few exceptions you do not need to connect to a specific server in order to see other pilots who are on that server. For best performance, you should connect to the server that is either geographically closest to you, has the lowest latency (ping time), or is the least busy.

Tip  Use this link to check if the MP servers are online. Page is automatically generated. The in-sim dialog will only display servers that are available.
Server address Status Location Tracked (by unless otherwise specified) Maintainer Maintainer's IRC name Maintainer's forum This is a link to the FlightGear forum. name Comments Up Germany Yes Oliver Schröder os N/A None Up Los Angeles, USA N/A Lloyd Stevens ls4680 ls4680 None Up Germany Yes Hergen N/A N/A Up UK No Jon Stockill Nav JonS This is a link to the FlightGear forum. None Down Chicago, USA N/A Brant IonCannon218 N/A None Down Berlin, Germany N/A Sven Teichmann N/A D-SAMI This is a link to the FlightGear forum. Unlimited traffic Down Wisconsin, USA N/A Tom Betka TB N/A Offline Down Frankfurt am Main, Germany N/A Roland Quix0r Quix0r This is a link to the FlightGear forum. 10 TByte traffic, mostly short pings Down Köln, Germany N/A Daniel Vigano Fauchi95 N/A Offline Down Montpellier, France N/A Alexis Bory xiii xiii This is a link to the FlightGear forum. None Down Vilnius, Lithuania N/A Darius N/A ffg This is a link to the FlightGear forum. None No Amsterdam, the Netherlands No ( Rob evilslut N/A Formerly[1] Up Beauvais, France N/A Charles Ingels charles cbz-026 This is a link to the FlightGear forum. None Up UK No Pete N/A N/A None Up North Point, Hong Kong Yes Hazuki Amamiya Hazuki Hazuki This is a link to the FlightGear forum. None Down Kansas City, Missouri, USA N/A Rob Rozestraten truthsolo truthsolo This is a link to the FlightGear forum. Offline Down Cluj, Romania N/A Marius tuxum tuxum This is a link to the FlightGear forum. Offline Down Germany N/A N/A N/A N/A N/A Up London, UK Yes Marisa Giancarla marisag marisag This is a link to the FlightGear forum. Up South San Francisco, California, USA Yes Marisa Giancarla marisag marisag This is a link to the FlightGear forum. None Up Tokyo, Japan Yes Marisa Giancarla marisag marisag This is a link to the FlightGear forum. None Up Munich, Germany No Fabian Gilgen ivelischt ivelischt None Up Mumbai, India Yes Marisa Giancarla marisag marisag This is a link to the FlightGear forum. Up Frankfurt, Germany Yes Marisa Giancarla marisag marisag This is a link to the FlightGear forum. Up Atlanta, Georgia, USA Yes Marisa Giancarla marisag marisag This is a link to the FlightGear forum. Up London, England Yes Megaf Megaf Megaf This is a link to the FlightGear forum. 2000 nmi Range and Radar Range. Up Shanghai, China No Weihao Lee N/A N/A 100 nm Range and 2000nm Radar Range. Up NewYork, US No Sidi Liang N/A sidi762 This is a link to the FlightGear forum. 200 nm Range and 2000nm Radar Range.

Geographic locations of the servers are also available at Google Maps.

If you are interested in hosting your own multiplayer server, you may want to check out Howto: Set up a multiplayer server.

Known issues

Fibertel (Argentina)

In December 2014, it was reported that UDP connection through port 5000 was not possible for users whose ISP was Fibertel This is a link to a Wikipedia article (Argentina).

Fibertel Argentina apparently uses the port for setup purposes. "It should be open for the user but it might not be fully functional."

Port 5000 is a generic port, and neither FlightGear nor the UPnP This is a link to a Wikipedia article protocol are an "official" usage of the port.

A solution would be to spread the ports between the servers; e.g., → 5001, → 5002

See also the forum thread This is a link to the FlightGear forum. and ticket #1617.

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