I hadn't heard anything about that, so I looked it up. Here's what I found:
Did the Incas Build Aircraft?
Comment: I found only a couple of websites that discussed the "Incan airplanes." This is the kind of Internet posting I take with a shaker full of salt. It would be easy for someone to fake. Until I see the information in a scientific journal, or at least the National Geographic, I doubt it's real.
The page appears to have been put together by someone named Nicole Coleby. I don't claim that she's perpetuating a hoax, although she may be. It's just as likely that she's repeating rumors she's heard from a follower of Erich van Daniken. She's posted drawings by someone named Lumir G. Janko, so perhaps he's the source of the "airplanes."