PARIS/LONDON, Jan 6 (Reuters) - Qatar Airways is claiming $618 million in compensation from planemaker Airbus in a dispute over erosion to the surface of A350 jetliners, a court document showed on Thursday.

The Gulf airline is also seeking extra compensation of $4 million for every day that 21 of its A350 airplanes remain grounded by Qatar's regulator over the skin damage, which includes erosion and gaps in a layer of lightning protection. (Reporting by Tim Hepher and Guy Faulconbridge Editing by David Goodman )