I do this a lot and prefer to check them rather than get turned around at the gate to go check it.
However small travel rod cases are OK lately. Spey do not fall into this category.
I pack the rods in a suitable container like a triangular tube, hard plastic rod case, or double-walled rod shipping carton depending on the number of rods.
Sage makes a really nice travel tube 4" up to 63" which should take care of just about anything a two-handed enthusiast would care to travel with, I would think. I plan to get one for my "light travel" case :hihi: