Learn Spanish (Latin America): Si el radar hubiera funcionado, habría advertido al capitán. - If the radar had worked, it would have warned the captain.

This sentence sets up a hypothetical situation in the past because the radar didn't actually work. To express 'if something had happened', Spanish uses si followed by the past perfect subjunctive (hubiera plus a past participle). Using the indicative había funcionado after si is grammatically incorrect for impossible past events.

What tense is habría advertido and why is it used here?

Habría advertido is the conditional perfect, meaning 'it would have warned'. In 'if' sentences about the past, this tense is used for the result clause to express what would have happened if the hypothetical condition had actually been met.

Can I say si el radar hubiese funcionado instead?

Yes. Both hubiera and hubiese are correct forms of the auxiliary verb haber in the subjunctive mood. However, in Latin America, the -ra endings like hubiera are much more commonly used in everyday speech than the -se endings.

Why is it al capitán instead of just el capitán?