Be verb + to be的用法 - 文法教學區 - 英語討論區 - 台灣英語網 - English(英語) + .com(網際網路) + .tw(台灣)
There is, in Longman Dictionary, an explicit explanation of how to use this. Here it is. be to do something (formal) a) used to talk about arrangements for the future: *Audrey and Jimmy are to be married in June. *Two men are to appear in court on charges...