What ways are there to go about building a safe, reliable system to allow the flying mounts in D&D 3.5e to "fly blind" (i.e. in clouds, fog, rain, and snow, day and night) between preset destinations? Outlanding support is nice, but not strictly necessary.
All 3.5e books can be used, and spell or magic item research is allowed.
This is built for a public-use system that will be used day-to-day for mail, parcels, and small numbers of passengers. Occasionally, it'll be used for higher-risk missions such as search-and-rescue or medical evacuation.
Requirements of the system:
The system needs to be safe and reliable enough for its regular operations.
The system should be relatively inexpensive and mostly self-sufficient:
Pilots should be able to perform any magic required with UMD or basic spellcasting; 20th-level wizards, druids and clerics shouldn't be required.
The cost of equipment used in-flight should be covered by the price of deliveries, so as to keep the system self-sustainable.
Ground equipment can be more expensive, but costs should be kept relatively low in the ballpark of inns or roads. Epic level spells should be avoided in the creation of infrastructure.
Multiple mounts should be able to use this system simultaneously, although one-time registration of mounts is acceptable.
There needs to be a communication channel (air-to-ground at a minimum, air-to-air is a plus) available to the mount-riders.
Weather: This system must be able to work in all reasonable mundane weather. Fliers will steer clear of hail and lightning storms, but this system should be able to handle rain, fog, and wind.
Terrain: This should support multiple types of terrain: island chains, forests, tundra, desert, mountains, etc.