Why is the Spanish imperfect tense used in this sentence when it describes a specific, one-time past event: "Convoy donde viajaba a AMLO sufre accidente carretero."?

Answer 1

That is because there are 2 actions happening in the past. When one is a longer action, it goes into the imperfect. The interrupting action goes in the preterite tense.

For example:

Comía la cena cuando mi esposo llegó con una pizza.

I was eating dinner (longer action) when my spouse arrived (interrupting action) with pizza.

In English, we should do the same thing by using the past perfect to distinguish between 2 actions in the past, but often we will use the simple past and a time expression to show which happened first.

I hope that helps.

Sara