Translation:The plane is taking off soon!
She'll soon be here./She'll be here soon. https://dictionary.cambridge.org/dictionary/english/soon
The plane is going to take off soon. Really, Duolingo? will and going to?
As Gabrielle145359 mentioned above, it is part of the sentence structure 快要…了, which taken together indicate that the action described is imminent. (The combination 就要…了 means the same thing.)
To Duolingo: 'takeoff' is an acceptable form of 'take off' when related to flight.
"The plane is about to leave soon" was marked as incorrect. It has the same meaning. It should be accepted.
Airplane is taking off soon. Why is this wrong? Think it's the same meaning with the answer key.
I checked every [Report] box for lack of a way to report erroneous " You missed a space." where I wrote "plane's" instead of "plane is" which are both correct.
了 needs to be pronounced "le" here, not "liao". It's annoying how the course has bugs like this, that are just wrong.
要 in this context is part of the 快要…了 construction meaning "…will happen soon." It means "will," not "need"/"have to."
However, I suppose we need a native speaker to tell us whether your translation is technically also correct, even though that's not what this sentence usually means.