Explanation
Means 'when', 'while', or 'on the occasion of' a certain event or situation.
Formation
Verb-casual + 際に, い-Adjective + 際に, な-Adjective + な際に, Noun + の際に
Detailed explanation
～際に is used to specify a time or occasion when something happens. It’s more formal than a simple 'とき' and often appears in announcements or polite instructions.
Examples
Shuppatsu no sai ni, pasupooto wo wasurenai de kudasai.
When departing, please don't forget your passport.
Jishin ga okoru sai ni, sugu ni hinan shite kudasai.
When an earthquake occurs, please evacuate immediately.
Nihon e kuru sai ni, omiyage wo takusan kau tsumori desu.
When I come to Japan, I plan to buy lots of souvenirs.
Mensetsu no sai ni, suutsu wo chakuyou shite kudasai.
Please wear a suit when attending the interview.
Practice
Grammar content sourced from hanabira.org.