Translation:I go to the airport by bus.
I'm curious too-- if there's actually a way to differentiate in Japanese I would accept it as an error, but if not, it seems like "on a bus" and "on the bus" should both be accepted. (At least where I am in the US, you would almost always say that you "take THE bus" somewhere, unless it's a big inter-city megabus where you miiiiight say "take a bus" instead.)
The word order is a little odd in the Japanese. By putting バスで first you're emphasising the way you travelled over your destination. Your also have to try to reflect that in your English translation - I go by bus to the airport. It's a little odd. Also, 行きます is missing a す at the end.
That's word for word the same translation that Duolingo has above so should have been correct. It's possible that you accidentally missed out a word like to or the or misspelled them thanks to predictive txting - it's easy to do, especially on a cell or tablet or even if they have tiles. I often think I've typed it out exactly as they have it and then notice that I've inadvertently left out a small word or in my haste spelt the as hte and because my predictive is messed up from all the different languages I'm always typing on my phone, often it misses little things like this and doesn't correct them.
Shouldn't it be "kūkou made basu DE ikimasu"? ("De" as in particle for instrument) I feel that, if not, the way it is written translates to "I go to the airport bus" as the "by" is not used. Does anyone no why? I searched online and every sentence I found uses all types of vehicles with DE.
Would "I will ride the bus to the airport." work as well as translation? I entered that and it said it was incorrect, with the right answer being "I will take the bus to the airport." or "I go to the airport by bus." They all seem equally interchangeable to me but maybe I'm wrong if "ride" has it's own verb used differently or something... Do shed some light here, I'll mark the sentence for now though since I think it works.