Learn Hardcore Korean: eoje guknaeseon bihaenggireul tasseoyo.

In Korean, time expressions like 어제 (yesterday) usually come at the start to set the time frame. Korean has a flexible word order, but it’s common to front time adverbs for clarity or emphasis.

What does 국내선 mean, and how is this compound formed?

국내선 combines 국내 (domestic) + 선 (route/line) to mean “domestic route.” In aviation contexts, it refers specifically to a domestic flight route.

Why do we say 국내선 비행기 instead of just 비행기?

국내선 modifies 비행기, specifying “a plane on a domestic route.” In Korean, modifiers (like adjectives or noun modifiers) always precede the noun they describe: [Modifier] + [Noun].

What’s the function of -을/를 in 비행기를 탔어요?

-을/를 is the direct object marker. Here, 비행기를 marks “plane” as the object of the verb 타다 (to ride/board).

Why is the verb 타다 used with 비행기?

In Korean, 타다 means “to ride” or “to board” and is used with vehicles: 버스, 기차, 비행기, etc. So 비행기를 타다 literally means “to ride a plane,” i.e., “to take a flight.”

Why is the verb ending -었어요 used here, instead of -아요, -어요, or -았어요?

탔어요 is the polite past tense form of 타다 in the -아요/-어요 conjugation. Since 타다 has the vowel ‘ㅏ’, the past tense is formed as: 타 + 았 + 어요 → 탔어요.

Could we omit 비행기 and say 어제 국내선을 탔어요 instead?

Yes. 어제 국내선을 탔어요 is perfectly natural and means “I took a domestic flight yesterday.” Here, 국내선 itself becomes the direct object.

How would you make this sentence more formal?

In a more formal register, use -습니다 instead of -어요:
어제 국내선 비행기를 탔습니다.