Especially if you're in a smaller market, your best bet is to try to get yourself into an APD and/or Music Director role. Then you're basically 2nd in command. If the PD leaves and the management is pleased with your work, you're basically a shoo-in for the promotion to PD. Even though they still have to "officially" post the job, it's rare for a smaller market to hire an "outsider" as a PD, unless nobody on the existing staff wants it, or they're all seriously underqualified for it.
In medium and large markets, there's a better chance you could get outside applicants with previous PD experience, who could trump an insider with no PD experience. But it also depends on where these other folks are coming from, and how much of a salary they're expecting. For example, a top-20 market PD's resume might look impressive for an opening at a mid-60s market station. But you have to wonder why that person is leaving (or was forced out of) their cushy top-market job... and whether they're willing to work for half of what they were making before.
Now, in many cases, large-market stations do have PDs who are not on-air. In larger markets, it's possible for a PD to just be so busy with things, they don't have time for an air shift. But still, many come from backgrounds where they have been on-air before. After all, big-market PD's were all once small-market PD's.... and in almost every single smaller and medium market, PD's are also air talent.
