Pilots (or auto pilots) are in essence rule-based playlists. They automatically generate a list of random tracks according to specific rules you define. It's an easy way to fill the radio station's program with music during hours where there is no available DJ. Pilots can be as simple or as elaborate as you like. They can range from "shuffle all songs in the library" to things like "play 1 track by U2, then 3 indie rock tracks, then a jingle that matches the term 'rock' then one track that comes from a soundtrack and then repeat the same recipe".
Here is how a demo pilot looks:
As mentioned, pilots consist of rules which may be songs from a tag, keyword, album or an artist. These rules will repeat generating a list of songs for as long as the pilot is scheduled to play. When creating a pilot, you will get an indication of how may times it can create different loops without repeating the same song, or else you will get a warning of '0 matches' if you introduce a rule that matches no tracks. Pay attention in the case that you see the indication "unique loops:0" because this means that you need to re-consider the rules set and check if there are enough tracks matching your rules.
The idea behind pilots is that you can create many pilots based on your zones and you can schedule them. At the management area of the pilots you can see all the available pilots that you have created.
If you don't have something scheduled at your program, the default pilot is taking over. This is an important thing to setup for your radio station. Since you have set the rules for the default pilot, you can have in a sense control over what is playing even if you haven't scheduled something. At the example above, "Ballads" is the default pilot.
Check out more on how to create or edit a pilot here.