fly bridge vs flying bridge

fly bridge and flying bridge both are nouns.

Word	Noun	Adjective	Verb	Adverb
fly bridge	Yes	No	No	No
flying bridge	Yes	No	No	No

As nouns, fly bridge and flying bridge are synonyms defined as:

fly bridge and flying bridge: the highest navigational bridge on a ship; a small (often open) deck above the pilot house

Other synonyms of fly bridge include flybridge, monkey bridge.

fly bridge (noun)	flying bridge (noun)
the highest navigational bridge on a ship; a small (often open) deck above the pilot house	the highest navigational bridge on a ship; a small (often open) deck above the pilot house