O sistema do banco está fora do ar agora.

Because do is a contraction of de + o:

• de = of
• o = the
• de + o = do

So:

• o sistema do banco = literally the system of the bank
• In natural English, that usually becomes the bank’s system

Portuguese often expresses possession this way instead of using an apostrophe like English does.

Portuguese uses definite articles much more often than English.

So o sistema means the system, and in many everyday contexts Portuguese prefers that article where English might sometimes leave it out or use a possessive structure instead.

Here, o sistema do banco sounds natural because it refers to a specific system: the bank’s system.

Portuguese has two common verbs for to be: ser and estar.

Here, está is used because being fora do ar is a temporary state or condition. The system is down right now, not permanently.

So:

• está fora do ar = is down / is offline
• é fora do ar would be incorrect here

A good rule of thumb is:

• ser = identity, characteristics, definitions
• estar = current condition, location, temporary situation

Yes, it’s an idiomatic expression.

Literally, fora do ar means out of the air, but in real usage it means things like:

• offline
• down
• off the air
• not working
• unavailable

It can be used for:

• websites
• systems
• apps
• radio/TV broadcasts
• phone lines

So in this sentence, está fora do ar means the bank’s system is currently unavailable.

No. It is very common with technology, but not only with technology.

Examples:

• O site está fora do ar. = The website is down.
• A rádio está fora do ar. = The radio station is off the air.
• O sistema está fora do ar. = The system is down.

In Brazil, it is especially common for websites, apps, and computer systems.

Sometimes yes, especially in tech contexts, because offline is widely understood in Brazil. But fora do ar is more natural and more broadly used in everyday Brazilian Portuguese.

Compare:

• O sistema está fora do ar. = very natural, common
• O sistema está offline. = understandable, but more English-influenced

If you want the safest everyday phrase, use fora do ar.

Agora means now, and Portuguese allows some flexibility in where adverbs go.

These are all possible, though they can sound slightly different in emphasis:

• O sistema do banco está fora do ar agora.
• Agora o sistema do banco está fora do ar.
• O sistema do banco agora está fora do ar.

The version with agora at the end is very natural and often puts the focus on the current moment: right now.

Yes. Banco can also mean bench or seat, depending on context.

But in this sentence, banco clearly means bank because of sistema. A system strongly suggests a financial institution, not a bench.

So context usually makes the meaning obvious.

Not with exactly the same meaning.

• o sistema do banco = the system of a specific bank
• o sistema bancário = the banking system in general, or the banking system as an industry/sector

So if you mean one bank’s computer system is down, o sistema do banco is the right choice.

It is neutral and very natural. You could use it in everyday conversation, customer service, work, or even in a written message.

It is not slangy, even though fora do ar is an idiomatic expression. It is standard, common Brazilian Portuguese.

If you wanted something a little more formal, you could say:

• O sistema do banco está indisponível no momento.

That means essentially The bank’s system is unavailable at the moment.

In careful pronunciation:

• está = eh-STA
• fora = FO-ra
• do = doo
• ar = ar

In natural Brazilian speech, the final r in ar is often pronounced like a soft h sound, depending on the region, especially in Rio and many other areas. So ar may sound a bit like ahh with a breathy ending.

Also, connected speech may make the phrase flow together smoothly:

• está fora do ar

The stressed syllables are mainly:

• es-TÁ
• FO-ra
• ar

Yes.

• O sistema do banco está fora do ar. = The bank’s system is down.
• O sistema do banco está fora do ar agora. = The bank’s system is down now / right now.

Adding agora makes the time reference explicit and emphasizes that this is the current situation. Without it, the sentence still works perfectly if the context already makes the timing clear.