on the occasion of; at the time of
出発に当たって一言挨拶をした。
As we set off, I said a few words.
開会に当たってお礼を申し上げます。
On the occasion of the opening, I would like to express my sincere thanks.
新年に当たって目標を決めよう。
With the new year upon us, let's set our goals.