FS2GDL90

fs2gdl90 broadcasts simulator data over UDP in GDL90 format for EFB apps such as ForeFlight, Garmin Pilot, WingX, and FltPlan Go.

The project has two simulator frontends over a shared GDL90, ForeFlight, settings, and UDP core:

• X-Plane 12 plugin frontend for macOS, Windows, and Linux
• Microsoft Flight Simulator 2020/2024 SimConnect frontend for Windows

The current codebase includes:

• Standard GDL90 heartbeat, ownship report, and ownship geometric altitude messages
• ForeFlight ID and AHRS extension messages
• ForeFlight auto-discovery with fallback to a manual target IP/port
• X-Plane traffic from TCAS targets, with legacy multiplayer fallback
• MSFS traffic from nearby SimConnect airplane and helicopter objects
• Shared JSON settings, validation, packet encoders, UDP transport, and unit tests
• X-Plane in-sim ImGui settings window and MSFS desktop ImGui status window

Release Installation

The recommended release layout keeps the simulator frontends separate:

fs2gdl90/
|-- xplane/
|   `-- fs2gdl90/
|       |-- mac.xpl
|       `-- 64/
|           |-- win.xpl
|           `-- lin.xpl
|-- msfs/
|   |-- fs2gdl90-msfs.exe
|   `-- SimConnect.dll
|-- README.md
`-- LICENSE

For X-Plane, copy the packaged xplane/fs2gdl90 folder into:

X-Plane 12/Resources/plugins/

After launching X-Plane, open:

Plugins -> FS2GDL90 -> Settings...

You can also toggle broadcasting from:

Plugins -> FS2GDL90 -> Enable Broadcasting

X-Plane settings are stored in the simulator preferences directory as:

Output/preferences/fs2gdl90.json

For MSFS, start Microsoft Flight Simulator, load a flight, then run:

msfs\fs2gdl90-msfs.exe

MSFS settings are stored by default under:

%APPDATA%\fs2gdl90\fs2gdl90-msfs.json

Quick Setup

For a basic manual setup:

1. Start the simulator frontend you use.
2. Set Target IP to the tablet or EFB device IP.
3. Leave Target Port at 4000 unless your app requires something else.
4. Keep NIC and NACp at 11.
5. Save the settings.
6. Confirm the status view shows packets being sent.

For ForeFlight, FS2GDL90 can listen for discovery broadcasts on UDP 63093 and temporarily switch the broadcast target to the discovered host and port.

Build From Source

The repository uses the X-Plane SDK from SDK/, the MSFS SimConnect SDK when building the MSFS frontend, and Dear ImGui under third_party/imgui.

Clone with submodules:

git clone --recursive https://github.com/6639835/fs2gdl90.git
cd fs2gdl90

Prerequisites

• CMake 3.16+
• C++17 compiler
• X-Plane SDK headers and libraries in SDK/ for the X-Plane frontend
• MSFS SDK with SimConnect for the MSFS frontend
• OpenGL development libraries on Linux

Platform notes:

• macOS: Xcode Command Line Tools
• Windows: Visual Studio 2022 or a compatible MSVC toolchain
• Linux: GCC 7+ or Clang 6+ plus OpenGL development packages

X-Plane Frontend

The X-Plane frontend is enabled by default:

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build --target fs2gdl90_xplane --config Release

Expected output locations:

• macOS: build/mac.xpl
• Linux: build/lin.xpl
• Windows: build/win.xpl or build/Release/win.xpl depending on generator

MSFS Frontend

Build the MSFS frontend on Windows with the MSFS SDK installed:

cmake -S . -B build-msfs -G "Visual Studio 17 2022" ^
  -DFS2GDL90_BUILD_XPLANE=OFF ^
  -DFS2GDL90_BUILD_MSFS=ON ^
  -DMSFS_SDK_PATH="C:\MSFS SDK"
cmake --build build-msfs --config Release --target fs2gdl90_msfs

MSFS_SDK_PATH should point to the SDK root that contains SimConnect SDK\include\SimConnect.h and SimConnect SDK\lib\SimConnect.lib. Building against the MSFS 2020 SDK is recommended for one binary that can run with MSFS 2020 and MSFS 2024.

For source builds, run:

build-msfs\Release\fs2gdl90-msfs.exe

Optional overrides:

fs2gdl90-msfs.exe --config C:\path\fs2gdl90-msfs.json --target-ip 192.168.1.50 --target-port 4000

Testing

Enable the test target with:

cmake -S . -B build -DFS2GDL90_BUILD_XPLANE=OFF -DFS2GDL90_BUILD_TESTS=ON -DCMAKE_BUILD_TYPE=Debug
cmake --build build --target fs2gdl90_tests --config Debug
ctest --test-dir build --output-on-failure

A coverage helper is available at scripts/coverage.sh. It configures a separate coverage build under build/coverage, runs ctest, and reports line and function coverage for src/. By default it enforces at least 97.5% line coverage and 100% function coverage, and you can override those thresholds with MIN_LINES_PERCENT and MIN_FUNCTIONS_PERCENT.

Runtime Behavior

Both simulator frontends send:

• 0x00 Heartbeat at the configured heartbeat_rate
• 0x0A Ownship Report at the configured position_rate
• 0x0B Ownship Geometric Altitude at 1 Hz
• 0x14 Traffic Report at 1 Hz
• 0x65/0x00 ForeFlight ID at 1 Hz
• 0x65/0x01 ForeFlight AHRS at 5 Hz

Current X-Plane behavior:

• ForeFlight auto-discovery is optional and listens on the configured broadcast port
• Manual target_ip and target_port are used as the fallback target
• The effective callsign uses the aircraft tail number when available, otherwise the configured fallback callsign
• Ownship report altitude uses sim/cockpit2/gauges/indicators/altitude_ft_pilot when available
• AHRS heading can be transmitted as true or magnetic heading
• Traffic is sourced from TCAS target datarefs when available, otherwise from legacy multiplayer datarefs

Current MSFS behavior:

• Connects to MSFS 2020/2024 through SimConnect from an external Windows executable
• Uses the same JSON settings schema as the X-Plane frontend
• Sends ownship GDL90 position, geometric altitude, ForeFlight device info, and ForeFlight AHRS
• Uses ForeFlight discovery on UDP 63093 when enabled
• Requests nearby SimConnect airplane and helicopter traffic once per second and sends best-effort GDL90 traffic reports
• Includes traffic injected by clients such as vPilot because those clients create/update nearby VATSIM aircraft as SimConnect AI sim objects
• Generates synthetic self-assigned traffic addresses when MSFS does not expose real ICAO addresses

Weather uplink data is not transmitted.

Configuration

The on-disk settings file is JSON:

{
  "target_ip": "192.168.1.100",
  "target_port": 4000,
  "foreflight_auto_discovery": true,
  "foreflight_broadcast_port": 63093,
  "icao_address": 11259375,
  "callsign": "N12345",
  "emitter_category": 1,
  "device_name": "FS2GDL90",
  "device_long_name": "FS2GDL90 AHRS",
  "internet_policy": 0,
  "ahrs_use_magnetic_heading": false,
  "heartbeat_rate": 1.0,
  "position_rate": 2.0,
  "nic": 11,
  "nacp": 11,
  "debug_logging": false,
  "log_messages": false
}

Field reference:

Key	Type	Notes
target_ip	string	Manual UDP target. Can be a unicast address, subnet broadcast, or 255.255.255.255.
target_port	number	Manual UDP destination port.
foreflight_auto_discovery	boolean	Enables the listener for ForeFlight discovery broadcasts.
foreflight_broadcast_port	number	Discovery listen port. Default is 63093.
icao_address	number	Stored in JSON as a decimal 24-bit value. The UI accepts hex such as 0xABCDEF.
callsign	string	Fallback only. Trimmed to 8 characters.
emitter_category	number	Valid range 0-39.
device_name	string	ForeFlight device name. Trimmed to 8 characters.
device_long_name	string	ForeFlight long name. Trimmed to 16 characters.
internet_policy	number	0=Unrestricted, 1=Expensive, 2=Disallowed.
ahrs_use_magnetic_heading	boolean	false sends true heading, true converts to magnetic heading.
heartbeat_rate	number	Must be greater than 0.
position_rate	number	Must be greater than 0.
nic	number	Valid range 0-11. 11 is recommended for EFB compatibility.
nacp	number	Valid range 0-11. 11 is recommended for EFB compatibility.
debug_logging	boolean	Enables debug logging.
log_messages	boolean	Enables raw message logging.

Data Sources

Key X-Plane datarefs used by the plugin include:

• sim/flightmodel/position/latitude
• sim/flightmodel/position/longitude
• sim/flightmodel/position/elevation
• sim/cockpit2/gauges/indicators/altitude_ft_pilot
• sim/flightmodel/position/groundspeed
• sim/flightmodel/position/true_psi
• sim/flightmodel/position/theta
• sim/flightmodel/position/phi
• sim/flightmodel/position/psi
• sim/flightmodel/position/indicated_airspeed
• sim/flightmodel/position/true_airspeed
• sim/flightmodel/position/vh_ind_fpm
• sim/flightmodel/failures/onground_any
• sim/aircraft/view/acf_tailnum
• sim/cockpit2/tcas/targets/*
• sim/multiplayer/position/planeN_*

Key MSFS SimVars used by the frontend include:

• PLANE LATITUDE
• PLANE LONGITUDE
• PLANE ALTITUDE
• PRESSURE ALTITUDE
• GROUND VELOCITY
• VERTICAL SPEED
• PLANE HEADING DEGREES TRUE
• PLANE HEADING DEGREES MAGNETIC
• PLANE PITCH DEGREES
• PLANE BANK DEGREES
• AIRSPEED INDICATED
• AIRSPEED TRUE
• SIM ON GROUND
• ATC ID
• VELOCITY WORLD X/Y/Z for traffic track and vertical speed

Repository Layout

.
|-- CMakeLists.txt
|-- SDK/
|-- docs/
|-- include/fs2gdl90/
|-- src/
|   |-- core/
|   |-- msfs/
|   `-- xplane/
|-- tests/
`-- third_party/imgui/

License

This project is licensed under the MIT License. See LICENSE.