Wash. Rev. Code § 14.08.020
The acquisition of any lands for the purpose of establishing airports or other air navigation facilities; the acquisition of airport protection privileges; the acquisition, establishment, construction, enlargement, improvement, maintenance, equipment and operation of airports and other air navigation facilities, and the exercise of any other powers herein granted to municipalities, are hereby declared to be public, governmental, county and municipal functions, exercised for a public purpose, and matters of public necessity, and such lands and other property, easements and privileges acquired and used by such municipalities in the manner and for the purposes enumerated in this chapter shall and are hereby declared to be acquired and used for public, governmental, county and municipal purposes and as a matter of public necessity.
RCW 14.08.020