In my medieval fantasy world, airships are efficient and entrenched in the economy of trade and commerce. However, coordinating air travel on certain routes and prevailing winds seems difficult, especially considering that this world lacks much of what modern air traffic control uses to coordinate travel in airspace (ie. radio communication, high powered light, etc).
How would a medieval society coordinate/communicate with these airships? Would this process be possible on a wide scale? Is there real-life precedent for this?
For a basis on the general technological level, refer to late Imperial China (Ming/Qing Dynasty). This world also has a strong light-weight substance which the airships are made out of and an abundance of non-flammable gas that is lighter than air.