The flying shuttle employs a track (the "race") which runs along the front of the beater, from side to side. The shuttle travels in this track. The lower threads of the shed rest on the track and the shuttle slides over them. This allows for weaving on a wide loom without having to physically move from one side to the other in order to "throw" the shuttle.
Add a fly shuttle raceway to your Louet Spring Loom (not the Spring II) with this upgrade kit. Does not include a fly shuttle.