Absence of subject marker?

Question

This sentence with a relative clause is intriguing me:

비행기를 보는 사람이 많습니다. [pihaenggi-reul po-neun saram-i manh-seumni-da]

I know that this means "There are many people who are looking at the airplane". In this sentence, 는 qualifies the preceding sequence "are looking at the plane" as the relative clause. Presumably, 이 is the verb "to be". But why is there no particle 가 before the verb and after 사람?

I saw a second sentence, which is as follows:

착륙하는 비행기가 많습니카? [ch'angnyuk'ha-neun pihaenggi-ga manh-seumni-kka]

"Are there many airplanes (which are) landing?". Here, the syntactic function of the words is clear-cut. 는 standing for the relative clause, 가 standing for the subject, with the verb "to be" omitted before the adjective 많 ("many").

So, in the first sentence, the subject particle 가 is omitted and the noun 사람 is directly followed by the verb 이. While in the second sentence, the subject particle follows the noun 비행기 and the verb is omitted.

I have no doubts about the second construction, since the verb "to be" can be omitted before an adjective. But why is the subject particle omitted in the first sentence?

Answer 1

비행기를 보는 사람이 많습니다. [pihaenggi-reul po-neun saram-i manh-seumni-da]

Presumably, 이 is the verb "to be"

Here, 이 is the subject marker. 많습니다 on its own conveys the full meaning of 'there are a lot', so there's no need for another verb 'to be'.

착륙하는 비행기가 많습니까? [ch'angnyuk'ha-neun pihaenggi-ga manh-seumni-kka]

with the verb "to be" omitted before the adjective 많 ("many").

There's no 'to be' being omitted; English has the 'to be + adjective' construction, but Korean has descriptive verbs that stand alone without 'to be'.

the subject particle follows the noun 비행기 and the verb is omitted.

The verb is 많습니까 - a descriptive verb meaning 'to be numerous', here in question form with the 니까 ending.

since the verb "to be" can be omitted before an adjective

In my opinion, thinking of Korean descriptive verbs as the equivalent of English adjectives can be confusing if it means you expect them to work in the same way as English adjectives. I much prefer to think of words like 많다 as descriptive verbs.