They don't need to surcharge- if necessary they can just make an adjustment to their 'floating fares' (fares set according to route and load factor and continually adjusting themselves). Why they don't hedge? I would guess it costs money. Sometimes you win and sometimes you lose. It's like insurance- look at the industry that has built up around that- all living off insurance premiums. Maybe we'd all be better off if none of us insures anything at all. If an industry lives off hedging premiums, maybe in the long run if you never hedge, you've unloaded yourself of that expense.