I'd like to make a reservation to Los Angeles for Monday.

我想预订一张周一去洛杉矶的机票。

Just a second and I'll check the schedule.

请等-等，我来查-下时刻表。

I need an economy ticket with an open return.

我要一张经济舱、返回时间不定的往返票。

Air China has a flight leaving at 9:25.

中国航空公司有一班飞机，9:25起飞。

I guess that's OK. What time should I check in?

我想正合适。我应该什么时候办理登机手续呢?

You have to be there half an hour before departure.

你要在起飞前半小时到那里。

departure n.离开，出发;背离，违反