"I read it on the plane."
Translation:Ich lese es im Flugzeug.
"on the plane" is dative case. "im" translates to "in the" and "am" translates to "on the" for a dative case preposition. Could anyone please tell me why "im" is used here, apart from it being one of the frustrating thousands of vagaries of the German language.
When you're flying, you are inside a powered, fixed-wing aircraft that is propelled forward by thrust from a jet engine, propeller or rocket engine, hence you are in it in German (or an Bord).
Yes. I thought that might be the case. However why then wasn't the Duolingo question "I read the book in the plane". Or is it part of Duolingo practice to reword and convert their questions into perfect German logic?
I think that's roughly the idea. Some things are said in different ways in different languages, so it makes sense to learn them in the "right" way. It's not because of any "perfect German logic", as Duo usually also follows the German wording when it seems less logical, e.g. "I'm fine" = "Mir geht's gut" or "Es geht mir gut", lit. "Me goes it well" or "It goes me well"....