Helicopters is a plural noun. The singular form is helicopter.
Helicopters can land on any surface that's firm and flat enough. A dedicated spot for helicopters to land on is called a helipad or a heliport. They're often a part of a regular Airport.
The part of speech for this particular word is a noun.
part of speech
The part of speech for "answer" is a noun.
adverb
what part of speech is beneath
The part of speech for "unfamiliar" is an adjective.
The part of speech of "came" is a verb.
The part of speech for "twirl" is a verb.
The part of speech for "explicit" is an adjective.
The part of speech for "indefinite" is an adjective.
The part of speech for "lecturer" is a noun.