Communications

Summary
Messages of state are written, sealed, and couriered by flying Theurge; others go by riders or boat, often paying to use the Syntechnia network. There is no equivalent of heliography or other primitive telecommunication. Theurges can make their voices loud enough to be heard over long distances, but thankfully for the otherwised deafened populace that’s not standard practice. (source)

Airspeed
I think we’re talking human cannonball speeds rather than jet speeds–say, up to around 100 mph. So messages can take a while to get to the Halassurq front. (source)

Navigation
Telos-sense will keep a flying Theurge from running into a mountain even in poor visibility conditions and makes it easy to e.g. follow a coast, but in terms of not getting lost while flying inland they usually have to navigate visually, with a map and compass to hand to keep them from getting disoriented in unfamiliar terrain. Flying in bad weather or at night is possible but runs a higher chance of realizing when the sun comes up that you’re hopelessly lost. They don’t use special landmark towers; towns and villages make good enough landmarks for such purposes. (source)