Ultralight: A minimalist aircraft with a weight of roughly a thousand pounds or less. The United States Ultralight Association has photographs of a variety of designs. Descended from hang gliders, ultralights and microlights typically have tubular aluminum frames, fabric covered wings and open seating rather than an enclosed cockpits. They are not built for speed or comfort, but they will put a grin on your face. Rules vary from country to country, but they are generally less stringently regulated than conventional airplanes. Canadian authorities register them in a separate class; American regulations don’t require them to be registered at all. The Wright brothers would have given their teeth for one of these, or even a good look at one.
Tech Level: Fairly low, in that advanced metalworking is not required, but you do need a lightweight engine, so Dieselpunk as a starting point, with great Post-Apocalyptic potential. Human-powered ultralights are possible, which gets us off the hook for a lightweight power plant, but the tech level rises towards composite materials in other areas because of the need for a very light and efficient airframe, transmission and propeller.
Appeared In: Emergence, by David R. Palmer (1984). After a biowarfare apocalypse, a young girl discovers she is evolved beyond ordinary humans, learns to fly an ultralight, and sets out to find more of her kind. Note: when I went looking for this book online, paperback editions were mainly listed for $130 and up, with some premium copies priced at over $4000.
For Your Plot: Yay! Your hero can teach himself to fly an ultralight by trial and error. While being pursued by dystopian slavers on dirt-bikes. Through the radioactive badlands, because he’ll need some rough terrain to outrun a motorcycle. And he’ll have to turn the tables on one of those bikers if he wants to refuel.