To denote future actions viewed from the past, with verbs of motion (to arrive, to come, to go, to leave, to return, etc.), usually if the action is planned or expected.
But, the past continuous is rather frequent in adverbial clauses, introduced by the conjunction while, as, when, as long as, etc.: While they were talking, the boy waited outside. The artist (draw) ______ a picture of sunset yesterday. I (feed) ______ birds at the park every day since I (lose) ______ my job. Ann (wake up) ______ late and (miss) _______ her breakfast on Monday. I (forget) ______ to turn off the stove after dinner. I (see) ______ this film and I don’t want to see it again. Jazz (originate) ______ in the United States around 1900. Tom Hanks (win) ______ an Oscar several times already. Long ago, they (build) ______ most houses out of wood. Scientists still (not/find) ______ a cure for cancer. But the students in my class are really nice and I'm happy here now. At first I (not like) it because I (not have) any friends here. Andy: No, (I/have) ________ it for about a year, but ( I/not play) _______ with it very much. Then I understood that they were not returning either that year or the next. If no future reference of the action is evident, it implies that though the action was planned, it was not and will not be carried out:“Listen”, I said. Joanna was coming up too but was prevented.” I said quickly: “She was coming to tea yesterday afternoon.” (was due to come, but did not).§ 36. In all its uses the past continuous is translated into Russian by means of the past tense of the imperfective aspect.§ 37. The past perfect is formed analytically by the auxiliary to have in the past indefinite and participle II of the notional verb.As follows from the meaning of the past continuous and from its uses described above, it cannot denote a succession of past actions. The interrogative and negative forms and built in the way usual for all analytic forms. In all its uses the past perfect denotes actions the beginning of which (always) and the end (usually) precede a certain moment of time in the past. The fire began at midnight when everybody was sleeping. In these examples the moment of time is specified directly, by means of adverbials of time or indirectly by some other past action mentioned in the same sentence. The enormous black bull was galloping towards me at full speed. to) or adverbs (all day long, the whole night, etc.)We were quarrelling all day long yesterday. When actional durative verbs take the form of the past continuous the actions thus described do not actually differ from those in the form of the past indefinite, as both denote continuous actions in progress at some moment of time in the past: When I saw him, he was standing by the door. However in a complex sentence with a subordinate adverbial clause of time if the predicate verbs both in the principal and in the subordinate clauses express simultaneous continuous actions in progress it is usual (though not obligatory) to use the past indefinite in both the clauses: While I ate and drank, I looked up the register. To denote a continuous action in progress at a certain moment in the past. When I called him up, he was still having breakfast. The difference between the two is that the past indefinite lays stress on the fact, while the past continuous emphasizes the process, thus presenting the action more vividly. I ______ (want) to go there last summer but I couldn’t. His father ________ (come back) to London last Sunday. Yan __________ (write) a letter to Nick two days ago.