Für den Anschlussflug muss ich das Terminal wechseln.

Because für always takes the accusative case in German.

• The noun is der Anschlussflug in the nominative.
• Anschlussflug is masculine.
• Masculine accusative changes der to den.

So:

• nominative: der Anschlussflug
• accusative after für: den Anschlussflug

That is why you get für den Anschlussflug.

German very often combines nouns into compound nouns.

Here:

• Anschluss = connection
• Flug = flight

Together, Anschlussflug means connecting flight.

This is completely normal in German. Instead of writing several separate words, German usually joins them into one noun, and the last part decides the gender. Since der Flug is masculine, der Anschlussflug is also masculine.

German main clauses usually place the finite verb in second position.

In this sentence, the first element is:

Für den Anschlussflug

So the finite verb must come next:

muss

Then comes the subject:

ich

Structure:

• 1st position: Für den Anschlussflug
• 2nd position: muss
• then: ich
• then the rest: das Terminal wechseln

So German is not counting individual words here; it is counting sentence elements. The whole phrase Für den Anschlussflug takes the first slot.

Yes, that is also grammatical.

Both are correct:

• Für den Anschlussflug muss ich das Terminal wechseln.
• Ich muss für den Anschlussflug das Terminal wechseln.

The difference is mostly focus or emphasis.

• Starting with Für den Anschlussflug highlights the reason or situation.
• Starting with Ich is more neutral and straightforward.

German often moves different elements into first position depending on what the speaker wants to emphasize.

Because Terminal is a neuter noun in German: das Terminal.

So:

• nominative: das Terminal
• accusative: das Terminal

For neuter singular nouns, the article does not change between nominative and accusative.

That is why it stays das.

It actually is in the accusative, but for neuter singular nouns, nominative and accusative look the same.

With wechseln, the thing you change or switch is the direct object, so it takes the accusative.

Compare:

• nominative: das Terminal
• accusative: das Terminal

So the case changes in function, but not in form.

Here wechseln means to change or to switch.

So das Terminal wechseln means to change terminals or to switch to a different terminal.

In travel situations, German often uses wechseln for moving from one terminal, train, room, lane, or platform to another.

It is a very natural verb here.

No. Wechseln by itself is not separable.

That is why in this sentence it stays together as a normal infinitive at the end:

muss ich das Terminal wechseln

By contrast, a separable verb would split in a main clause, such as:

• Ich steige um.

But wechseln does not do that.

Because this sentence contains a modal verb: muss.

With modal verbs in German:

• the modal verb is the finite verb
• the other verb goes to the end in the infinitive

So:

• muss = finite verb, in second position
• wechseln = infinitive, at the end

This is a very important German pattern:

• Ich muss gehen.
• Wir wollen essen.
• Sie kann kommen.

Your sentence follows the same rule: Für den Anschlussflug muss ich das Terminal wechseln.

Usually not with the same meaning.

Umsteigen means to change from one train, bus, plane, etc. to another. It focuses on changing transport/connections.

But das Terminal wechseln specifically means changing terminals inside the airport context.

So:

• umsteigen = change vehicles / make a transfer
• das Terminal wechseln = move to another terminal

They are related ideas, but not identical.

Because this is just one main clause, and German does not put a comma after an introductory phrase like Für den Anschlussflug.

English sometimes uses commas more freely for readability, but German is stricter about comma rules. Here, no comma is needed:

Für den Anschlussflug muss ich das Terminal wechseln.

Here it is best understood as the context/purpose: for the connecting flight.

It tells you in connection with what the terminal change is necessary.

It does not sound like a precise time expression. It is more like:

• for my connecting flight
• in order to catch the connecting flight
• because of the connecting flight situation

So it gives the practical context for why the speaker has to change terminals.

Yes. Very naturally, you could say:

Für meinen Anschlussflug muss ich das Terminal wechseln.

Here, meinen is used because:

• für takes the accusative
• Anschlussflug is masculine
• masculine accusative with mein becomes meinen

This version can sound a bit more personal or specific than just für den Anschlussflug.