Trajectory decides how far the fly has to fall once the loop opens — and that fall is where accuracy is lost. Cast flat and the loop falls a bit, but the fly is still far above the target when it opens and must drop a considerable distance — the odds of it landing straight on the target are not high in wind. Tilt the casting arc so the rod tip path aims down at the target, and the line and leader unroll much closer, leaving a short fall.

The fly leg of the loop goes where the rod tip path points, so you change trajectory by changing the orientation of the casting arc. How much depends on distance:

• Short casts (20 ft): a steep pitch, up in back and down in front.
• Long casts (45 ft): a shallower pitch.

Tasks 12 and 13 ask for 20, 30 and 45 ft targets, each needing its own trajectory change. Loop control matters too: the guide ties straight fly legs to the most accurate loops.

Source

From the CI Study Guide (2025) (PDF), “Varying Casting Arc and Trajectory” and Tasks 12–13; terms from the FFI Fly Casting Definitions (Trajectory).