Future in the Past is used to express the idea that in the past you thought something would happen in the future. There are different forms of future in the past, all of which correspond to forms that we usually use to refer to the future. The process is the same as that used for converting direct speech to indirect/reported speech:
Am/Is going to = was going to Are going to = were going to Present continuous (am/is meeting) = past continuous (was meeting) Present continuous (are meeting) = past continuous (were meeting) Future simple (will) = would
Examples:
Tom decided spontaneously that he was going to fly instead of going by train.
Tom was going to phone at nine but he must have forgotten to.
