​Применяется в случаях:

​1.Продолжающееся действие в определённое время в прошлом

At nine o’clock yesterday morning, the plane was flying to Paris from New York.

​2. Действие в прошлом, прерывающееся другим действием (Past Simple)

He was reading a newspaper when his brother came.

3. Два действия или более, происходящие одновременно

   He was listening carefully while they were explaining the plan to him.

​4. Вводная информация в рассказе, повествовании

The sun was shining and the birds were singing. Tom was driving his old truck through the forest.

​5. С обстоятельствами времени: while, when, as, all day / night / morning, yesterday

She was trying to open the bag while he was checking the passport.