Franz Josef Airport is really only suitable for light aircraft. Mind you, Mount Cook Airport is just on the other of the mountains, and a scenic flightseeing trip can often be arranged at short notice.
By car
By car
It is about a thirty minute trip from Fox Glacier.
It is about a three hour trip from Greymouth.
Its about a four and a half hour trip from Wanaka.
Its about a six hour drive from Christchurch
By bus
By bus
Tour buses generally make Franz Josef one of their stops, either for the night or at least a lunch break. Alternatively, for a really cheap option, try nakedbus.com - bus services start at $1.