Learn Hardcore Icelandic: Flugvöllurinn er langt frá borginni.

This is how Icelandic marks the definite article. Instead of placing “the” before the noun, Icelandic attaches it as a suffix.
• Flugvöllur = “airport” (indefinite)
• Flugvöllurinn = “the airport” (definite)

What part of speech is er, and how is it used here?

Er is the present tense form of the verb vera (“to be”). In this sentence it functions as the copula, linking the subject (Flugvöllurinn) with the predicate (“far from the city”).

Why is langt used instead of langur, which I thought means “long” or “far”?

In the phrase vera langt frá (“to be far from”), langt is actually the neuter singular form used adverbially. Think of it as a fixed expression meaning “far.” When you use langur attributively (before a noun), you’d adjust gender, number and case—this isn’t that situation.

What case does the preposition frá require, and why is borginni in that form?

Frá always takes the dative case. The noun borg (“city”) in the dative singular definite form becomes borginni.
Declension at a glance for borg:
– Nominative ind.: borg
– Nominative def.: borgin
– Dative def.: borginni

Could I say Flugvöllurinn er langt frá borg (dropping the article on “city”)?

Yes, that’s grammatically possible. In that version, borg without a suffix is the indefinite dative, so it would mean “The airport is far from a city” or “from cities in general.” To refer to a specific city (“the city”), you use borginni.

Is the word order here the same as in English?

Very similar. Both languages use Subject–Verb–Adverbial in this sentence. Icelandic also enforces the V2 rule (verb-second), so the verb er appears in second position no matter what starts the sentence.
Example:
English: The airport (S) is (V) far from the city (Adv.).
Icelandic: Flugvöllurinn (S) er (V) langt frá borginni (Adv.).

How do I pronounce Flugvöllurinn er langt frá borginni?

Here’s a rough phonetic breakdown using an approximate English guide:
FLOOG-vuh-TLUR-rin AIR ah-LAHNGT frow BOR-gin-nee
Key points:
• ö is like the “i” in “bird” (without the r)
• ll in this environment is a voiceless lateral fricative (like a soft “tl”)
• r is rolled/trilled
If you want IPA, it looks roughly like:
/flʏɡˈvœtːɬɪrɪn ɛr laŋ̥t frau ˈpɔrkɪnɪ/