~場合は means "when an event ( ~ ) occurs; in case ~". It is not used for past events.
When there was an accident last year, many people died.
If an accident should occur, many people will probably die.
*Nonpast affirmative na-adjectives and nouns A(な)な場合は and Nの場合は, respectively.
会社を休む場合は、理由を言ってください。
In the event that you are absent from work, please tell us the reason.
お金がない場合は、友だちにかしてもらいます。
If I don't have money, I'll have a friend lend me some.
お金が必要な場合は、知らせてください。
In case you need money, let me know.
欠席の場合は、早く返事をしてください。
In the event that you cannot attend, give us a prompt reply.
Lesson 15-4「ビザをとる時、大使館に行かなければなりません。」
We have to go to the Embassy when getting a visa.