Okay one thought .... the others had james and kate hauling rocks.. later we find out it was for a runway...

so did the others no about the Airja Flight

did they know that it needed to land and then take off form there

makes me wonder

That was always my assumption. Given what we learned in the final season, I think Smokey must have somehow convinced Ben to have it built.

The reason given for it at the time was that their boat was gone. I don't think we have any evidence that Ben knew anything, although he could have been given orders. But like most "could have" theories, if the writers had wanted to set that up, they could have, and didn't.

I would speculate that the writers always knew they might be bringing in another plane or flying away in a plane, and they decided to establish the existence of the runway. (Checkov's Gun)

It didn't need to be justified by much (to the viewers) at the time, as the Others were so good at playing mind games. What mattered was for there to be a viable runway on the island, so that the writers could use it later.

This is an example of where the writers could have put in a little dialogue from Smokey and "reveal" that he manipulated the Others into doing this job, but they missed the opportunity.