Future In The Past
We use different structures to talk about the future in the past:
WOULD + infinitive
WAS/WERE + GOING TO + infinitive
Future in the past is used to express the idea that in the past you thought something would happen in the future. It does not matter if you are correct or not.
"Would" is used to express an expectation or possibility, not necessarily a plan.
It is often used with verbs of thought (know, think, hope, suspect etc.) in the past simple
This structure can also be used to express something that is still true.
Was/were going to
"was going to" is used to describe a future plan or intention relative to the time of speaking.
This often used when the anticipated event did not actually happen.
Both forms can be used to make predictions about the future.
Future in the past structures are not used with time clauses such as before, by the time, as soon as, after, unless. If you need a to make reference to time the Past Simple or Present SImple should be used depending on whether the future activity mentioned has happened or not.