This looks like slipped wing, also called angel wing or aeroplane wing. It is caused by a dietary imbalance when the bird is growing, often by too high a protein level, especially with a largely herbivorous species like a Black Swan. It can be corrected at an early age by taping the wing in the correct position, but with an adult bird like this, the only acceptable solution is amputation, even if it results in a double pinioned bird. Clipping the primary flight feathers takes the weight off, and may make the bird less uncomfortable, but is no substitute for surgery. Really, it should not be allowed to happen.
