Translation:Is the train station far away from the airport?
"far" and "far away" have the same meaning in English and should be accepted here. There's nothing in the Chinese that requires one to say "far away"
Is the airport far away from the train station? It is the same question in English, so why is one considered wrong?
I guess saying "is the airport far away from the train station" implies that you will be using the train station as your starting point or your point of reference.
It's not the same. You've switched subject and object. It might work in this situation, but you'll run into trouble if you don't learn the difference.
I used to learn from duolingo": Train stop so I use Train stop instead of train station every one can understand.
'Far away' means a great distance like from Beijing to London, not for something nearby as the distance from the airport to the train station in the same city.