RCW 47.68.170

The department may designate, design, and establish, expand, or modify a state airways system that will best serve the interest of the state. It may chart the airways system and arrange for publication and distribution of such maps, charts, notices, and bulletins relating to the airways as may be required in the public interest. The system shall be supplementary to and coordinated in design and operation with the federal airways system. It may include all types of air navigation facilities, whether publicly or privately owned, if the facilities conform to federal safety standards.