aircrewman vs navigator

aircrewman and navigator both are nouns.

Word	Noun	Adjective	Verb	Adverb
aircrewman	Yes	No	No	No
navigator	Yes	No	No	No

As nouns, navigator is a hyponym of aircrewman; that is, navigator is a word with a more specific, narrower meaning than aircrewman:

aircrewman: a member of an aircrew
navigator: the member of an aircrew who is responsible for the aircraft's course

Other hyponyms of aircrewman include bombardier, flight engineer.

aircrewman (noun)	navigator (noun)
a member of an aircrew	in earlier times, a person who explored by ship
	the member of an aircrew who is responsible for the aircraft's course
	the ship's officer in charge of navigation