If you mean "subsidized" because the airlines don't have to pay the kind of taxes on jet fuel that users of road (or rail) vehicles have to pay on gas, or that

If you mean "subsidized" because the airlines don't have to pay the kind of taxes on jet fuel that users of road (or rail) vehicles have to pay on gas, or that they only have to pay airport taxes, but can use the airways free of charge, then yes. But no-frills airlines like Ryanair are not in the charity business, so you can bet that their price calculation is economically sound on the whole.