Airports in the 30-40 km range from the city are not too uncommon, but beyond that the numbers start dropping off.

The only one I can think of (other than LCC airports in Europe - those don't count) that is well beyond that range is HIJ, which is a little over 50 km from downtown Hiroshima. It doesn't take all that long though, no more than an hour outside rush hour. You get out of the city pretty quickly and the highway moves fast. It just seems like you're driving through the hills forever before you actually get to the airport.