Last year I had the opportunity to encounter a set of five things. I learned that the names of these things are A, B, C, D, and E. In fact, these names were made verbally clear to me: “A as in Alpha, B as in Bravo, C as in Charlie, D as in David, and E as in Echo.” What are these things?
I read about these things in a Wikipedia article this week, which reminded me of my encounter from last year. Some of you might be familiar with these things. Others might need some more information than is offered in the previous paragraph. Feel free to ask yes-no questions, a la lateral thinking puzzles, in the comments.
life as a puzzle 
Do the five things form a complete set?
Is this set mostly familiar to people who share a particular interest of some sort? To people in a certain geographic area?
Complete set, yes. Familiarity related to interest and/or geography, yes.
Is each of the things bigger than a toaster?
Bigger than a toaster, yes.
Could any of the things fit inside a shipping container?
No.
Is there a unique instance of each of these things, or does each refer to a class/category of other things?
Sorry, forgot to make that a yes/no question. Is there a unique instance of each of these things?
The things in this set of five are not the only ones of their kind — similar ones outside the set also exist. Circumstances establish that that these five things (and no others) form a complete set together.
Do the items have anything to do with transportation? Do the items have anything to do with astronomy?
Transportation, yes. No to astronomy.
Are they Nvecbeg pbapbhefrf (Qnivq vafgrnq bs qrygn gb nibvq geniryre pbashfvba)?
Yes (naq pna lbh thrff juvpu nvecbeg)
Unegfsvryq?
Indeed.
Jangler got the answer, so I’ll restate it in non-ROT-13 format:
The things are the terminal concourses at Hartsfield-Jackson Airport. The public address in the airport tram service announces the names of the concourses at each station using NATO alphabet code (Alpha, Bravo, Charlie…) as a confirmation. But for Concourse D the address uses “D as in David” presumably to avoid confusion with Delta Airlines, the major carrier in Atlanta. Good work, everyone!