ACARS

Aircraft Communication Addressing and Reporting System client for Microsoft Flight Simulator. Connects to a running FSUIPC7 instance over WebSocket and streams real-time flight data including position, fuel state, and simulator time.

How It Works

FSUIPC7 exposes simulator memory through a WebSocket API. This app declares a set of memory offsets to read, subscribes to periodic updates (every 1 second), and outputs processed flight data to the console.

The system is aircraft-agnostic — it works with any MSFS aircraft (Fenix A320, FlyByWire A32NX, PMDG 737, etc.) because FSUIPC exposes common offsets that are consistent across all installed aircraft.

Communication Flow

MSFS <──> FSUIPC7 <──WebSocket──> ACARS Client

1. The client connects to FSUIPC7 via WebSocket
2. Sends an offsets.declare message registering which memory addresses to monitor
3. Sends an offsets.read message to subscribe to periodic reads at a given interval
4. FSUIPC7 pushes updates which the client processes and outputs

Output

Each update produces a structured object containing:

{
  date: "27/02/2026",           // Zulu (UTC) date — dd/MM/yyyy
  time: "14:30:45",             // Zulu (UTC) time — hh:mm:ss
  position: {
    latitude: 40.47218,          // Degrees (5 decimal places)
    longitude: -3.56124,         // Degrees (5 decimal places)
    altitude: 36012,             // Feet (nearest integer)
    heading: 247                // Degrees (nearest integer)
  },
  fuel: {
    centerKg: 2150,             // Centre tank fuel in kg
    leftMainKg: 3420,           // Left main tank
    leftAuxKg: 0,               // Left auxiliary tank
    leftTipKg: 0,               // Left tip tank
    rightMainKg: 3418,          // Right main tank
    rightAuxKg: 0,              // Right auxiliary tank
    rightTipKg: 0,              // Right tip tank
    totalKg: 8988               // Sum of all tanks
  }
}

Data Conversions

Field	Raw FSUIPC value	Conversion
Latitude / Longitude	64-bit float (degrees)	Direct from offset 0x6010/0x6018, rounded to 5 decimals
Altitude	64-bit float (metres)	value * 3.28084 to feet, rounded to nearest integer
Heading	64-bit float (radians)	value * (180 / PI) to degrees, rounded to nearest integer
Tank level	32-bit int	value / (128 * 65536) gives percentage (0–1)
Tank capacity	32-bit int	US Gallons
Fuel weight/gallon	16-bit int	value / 256 gives lbs/gallon
Tank fuel (kg)	—	percentage * capacity * lbsPerGallon * 0.453592

FSUIPC Offsets Used

Position

Offset	Size	Name
0x6010	8	Latitude (degrees, float)
0x6018	8	Longitude (degrees, float)
0x6020	8	Altitude (metres, float)
0x6038	8	Heading (radians, float)

Fuel Tanks

Offset	Size	Name
0x0AF4	2	Fuel weight per gallon (* 256)
0x0B74	4	Centre tank level
0x0B78	4	Centre tank capacity
0x0B7C	4	Left main tank level
0x0B80	4	Left main tank capacity
0x0B84	4	Left aux tank level
0x0B88	4	Left aux tank capacity
0x0B8C	4	Left tip tank level
0x0B90	4	Left tip tank capacity
0x0B94	4	Right main tank level
0x0B98	4	Right main tank capacity
0x0B9C	4	Right aux tank level
0x0BA0	4	Right aux tank capacity
0x0BA4	4	Right tip tank level
0x0BA8	4	Right tip tank capacity

Time (Zulu/UTC)

Offset	Size	Name
0x023A	1	Second (0–59)
0x023B	1	Hour (0–23)
0x023C	1	Minute (0–59)
0x023D	2	Day of month
0x0240	2	Year
0x0242	1	Month of year

Mock Server

A local development server is included that simulates FSUIPC7's WebSocket API without requiring MSFS or FSUIPC7 to be running. It serves pre-generated flight data that advances through a full simulated flight on each interval tick, looping back to the start once exhausted.

Simulated Flight

The mock server generates 7020 sequential FlightData records representing a 117-minute gate-to-gate Madrid (LEMD) to Barcelona (LEBL) flight. All values are in raw FSUIPC format (metres, radians, raw fuel integers) exactly as FSUIPC7 would emit them. Zulu time runs from 14:30:00Z to 16:26:59Z on 27 Feb 2026.

Phase	Time (s)	Duration	Altitude	Notes
Stand	0–300	5 min	610 m (field)	Parked at LEMD gate, hdg 180°
Pushback	300–360	1 min	610 m	Push and turn to taxiway
Taxi out	360–1260	15 min	610 m	Taxi to runway 32R
Takeoff & climb	1260–1860	10 min	610→10668 m	Rotate, climb to FL350
Cruise	1860–5460	60 min	10668 m	FL350, heading ~070°
Descent	5460–5940	8 min	10668→600 m	Descend for approach
Approach & landing	5940–6060	2 min	600→4 m	ILS 25R, touchdown at LEBL
Taxi in	6060–6960	15 min	4 m (field)	Vacate runway, taxi to gate
Parking & shutdown	6960–7020	1 min	4 m	Parked at gate, engines off

Position is linearly interpolated between waypoints using shortest-path angle interpolation for heading changes. Left and right main tank fuel levels burn linearly from 80% to 40% over the flight; all other tanks remain empty. The date is fixed at 27 Feb 2026.

Running the Mock Server

The server requires a pre-generated flight-data.json file. Run the generate step once before starting the server for the first time, and again any time you want to regenerate the flight data.

cd mock-server
npm install
npm run generate   # writes flight-data.json (7020 records, ~2.9 MB)
npm start          # reads flight-data.json and serves via WebSocket

flight-data.json is a generated artifact and is gitignored — it is not committed to the repository.

The server listens on ws://localhost:2048/fsuipc/ using the fsuipc sub-protocol — the same address and protocol the ACARS client is configured for by default. It handles offsets.declare and offsets.read commands and respects the requested interval.

Prerequisites

• Microsoft Flight Simulator (MSFS 2020 or 2024)
• FSUIPC7 running with WebSocket server enabled
• Node.js (v18+)

Setup

1. Clone the repository
2. Install dependencies:

   npm install

3. Edit src/config/sim_conn_details.json with your FSUIPC7 WebSocket host and port:

   {
     "host": "192.168.1.67",
     "port": 2048,
     "protocol": "fsuipc"
   }

4. Start MSFS and ensure FSUIPC7 is running
5. Run the client:

   npm start

Project Structure

src/
  index.ts                — Entry point: connects, subscribes, processes and outputs flight data
  config/
    sim_conn_details.json — FSUIPC7 connection configuration (host, port, protocol)
    variables.ts          — FSUIPC offset declarations (position, fuel, time) and read subscription
  connector/
    connector.ts          — WebSocket client (extends EventEmitter) wrapping the FSUIPC7 connection
  utils/
    constants.ts          — Conversion constants (LBS_TO_KG, FEET_PER_METRE, fuel divisors)
    conversions.ts        — Unit conversion functions (metresToFeet, radiansToDegrees, tankFuelKg)
    formatting.ts         — String formatting helpers (padZero)
  types/
    ConnectorClass.ts     — Interface for the Connector class
    FsuipcMessage.ts      — Generic message envelope type (command + name + data)
    topics/
      FlightData.ts       — TypeScript interface for the combined flight data payload
mock-server/
  server.ts               — WebSocket server that emulates FSUIPC7 for local development
  generate-flight.ts      — Generates 7020 FlightData records simulating a LEMD → LEBL flight
  package.json            — Standalone package with its own dependencies (ws, tsx)
fsuipc-vars.json          — Full dump of available FSUIPC simulator variables (L:Vars, H:Vars)

Tech Stack

• TypeScript with strict mode
• tsx for direct .ts execution (no build step)
• ws for WebSocket communication
• Node.js EventEmitter for internal message routing

License

ISC