VATSIM FSD Protocol Documentation

Updated January 2025

FSD is an application-layer TCP/IP protocol facilitating real-time communications between all clients connected to the VATSIM Network.

This documentation is reverse-engineered.

See openfsd for an alternative, free and open-source FSD server implementation.

For an introduction, see the About page.

This documentation is an independent work and is not affiliated with, endorsed by, or associated with VATSIM, Inc.