Learn Hardcore Russian: Самолёт летит над мостом.

The ending -ом shows that "мостом" is in the instrumental case. In Russian, when using the preposition над (meaning "over" or "above"), the noun that follows must be in the instrumental case.

Why is the preposition над used here and what role does it play?

Над means "over" or "above" and is used to indicate spatial relationships. In this sentence, it shows that the airplane is flying above the bridge and requires the following noun ("мостом") to be in the instrumental case.

Why isn’t there an article like "the" before "самолёт"?

Russian does not use articles such as "the" or "a/an." Nouns in Russian appear without an article, and any definiteness or indefiniteness is understood from context instead.

What is the form and tense of the verb летит in this sentence?

The verb летит is the third-person singular present tense form of the verb лететь (to fly). It is in the imperfective aspect, which indicates that the action is currently ongoing.

Is the word order in Russian flexible? Could this sentence be rearranged without changing its meaning?

Yes, Russian word order is quite flexible due to its rich case system that clearly marks the roles of words. Although Самолёт летит над мостом is the most neutral and straightforward way to express the idea, you could rearrange it (for example, Над мостом летит самолёт) for emphasis while still keeping the meaning intact.