The following sentence, which is found in a grammar test in a textbook for learners of English called Tourism 2 (OUP), is given by a tour guide as part of her explanation of a schedule:
As soon as we get to the station, we'll go to the hotel.
The same textbook contains the following as part of its Grammar Reference section:
will is not normally used to talk about timetables or planned events. We use will when we decide what to do at that particular moment, e.g. to promise or offer to do something, and to make requests.
Why do we use "will" future here, even though this is clearly not a decision being made at that particular moment. It's pre-planned.
Other future forms which are used to talk about arrangements (present continuous, "going to" future) don't seem to work in this sentence. Why not? Is it something to do with the fact that it's part of an independent clause that follows a dependent clause starting with 'as soon as'?