Meaning of 偶発時用手続 in Japanese

秋には木の葉が落ちる。
Leaves fall in the autumn.

何の用でここに来たのですか。
What has brought you here?

それから服を着て、講義用のメモを手さげ鞄に詰め込み、階段を駆け下りた。
Then he got dressed, stuffed his lecture notes into his briefcase, and ran down the stairs.

搭乗手続きをするのはどこですか。
Where is the check-in counter?

１２才の時彼は声変わりした。
His voice broke when he was twelve.