Molting is a natural part of the cycle, and can be a sign of weather changes, breeding or "spring cleaning" for the Macaw. It usually happens once a year, and usually extensive parts of the plumage are replaced, so I guess it could seem frightening. If this has happened before, and you so no other changes, give it a few days and see if there are new feathers and a dashing new look.
If not, you should bring in a professional.
