Learn Portuguese (Portugal): A que horas é o voo?

In Portuguese, when you ask what time an event happens, you must include the preposition a (at). It is just like how in English you answer with "The flight is AT five," but Portuguese requires the "at" right at the start of the question: a que horas.

Why is horas plural but the verb é (is) singular? Shouldn't it be são?

The verb always matches the main subject of the sentence, which here is o voo (the flight). Since the flight is singular, we use the singular verb é. You are literally asking "At what hours is the flight?"

Could I just use quando and ask Quando é o voo? instead?

Yes, you can! Quando means "when", so it works perfectly. However, quando is broader and someone might just answer "Tomorrow". Using a que horas specifically asks for the exact clock time.

Do I always have to put a que horas at the beginning of the question?

Not always! Portuguese word order is very flexible. It is completely normal and common to ask O voo é a que horas? by putting the subject first and the question phrase at the very end.