FlightAware is German? :) "fife"

If you hold your cursor over a flight’s call sign it’ll show it in the phonetic alphabet. I happen to stumble on this one.

‘Fife’ is the correct phoenetic pronounciation of ‘5’ per the ICAO/FAA radiotelephony phonetic alphabet.

So is “tree”, although FlightAware doesn’t show it like that.
and most people know “niner”

Good catch, I’ll get those fixed.

Whoa! “Tree” sounds like “three.”

That’s kinda the point, “tree” stands for three.