fly bridge vs bridge deck

fly bridge and bridge deck both are nouns.

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

As nouns, bridge deck is a hypernym of fly bridge; that is, bridge deck is a word with a broader meaning than fly bridge:

fly bridge: the highest navigational bridge on a ship; a small (often open) deck above the pilot house
bridge deck: an upper deck where a ship is steered and the captain stands

Other hypernyms of fly bridge include bridge.

fly bridge (noun)	bridge deck (noun)
the highest navigational bridge on a ship; a small (often open) deck above the pilot house	an upper deck where a ship is steered and the captain stands