Alidar Jarok wrote:
Yeah, when they landed on the Hydra island, I realized that the runway was the one that was dug. I wouldn't go so far as to say they planned that out from season 3, but I think someone realized at some point that it was a great idea to use it (solves a mini-mystery that I just assumed was going to be left as only something to bring Kate and Sawyer together).
Even if they hadn't planned on the Ajira landing in season five, the runway was definitely meant to be an important plot point to be set up for the future. On the DVD commentary, Damon Lindlof jokes with the cast about how they kept putting in a line about how they were building a runway, but the line kept getting cut in post-production, so they kept rewriting the line into every episode, confusing the cast who found themselves saying the same lines over and over again and reacting to the runway plan being revealed to them again and again. I think if it were that important to them to set up the runway they must have known it was going to be important down the road.