Learn Turkish: Kondüktör arka vagona geçmek üzere. - The conductor is about to pass to the back carriage.

The structure -mAk üzere (the full infinitive form of a verb followed by the word üzere) is the standard way to say someone is "about to" or "on the verge of" doing something. Here, geçmek (to pass) pairs with üzere to create "about to pass".

Why does vagon have an -a at the end (vagona)?

The verb geçmek (to pass, cross, or move to) involves motion toward a destination. In Turkish, you mark this destination with the dative case (-e/-a), which functions like the English "to" or "towards". Therefore, vagon becomes vagona (to the carriage).

Where is the word for "is" in this sentence?

In Turkish, the "to be" verb for the third-person singular (he/she/it is) is often invisible. The word üzere sits at the end of the sentence and acts as the main predicate. In highly formal writing or news broadcasts, you might see it written as üzeredir, but in everyday speech, the "is" is simply understood.

Could we say arkadaki vagona instead of just arka vagona?