Kada budem stigla na aerodrom, proveriću da li moj let kasni.

Because budem stigla is future II in Serbian.

In sentences like this, Serbian often uses future II in a subordinate clause introduced by words such as kada, ako, čim, or pošto, especially when that action will happen before another future action.

Here the order is:

• first: I arrive at the airport
• then: I check whether my flight is late

So Serbian naturally says:

• Kada budem stigla... = When I have arrived / when I arrive...
• proveriću... = I will check...

Using ću stići here would not sound right in standard usage for this kind of time clause.

Budem is a form of the verb biti (to be).

In this sentence, it is used to form future II:

• budem stigla
• literally something like I be arrived

The full pattern is:

• budem stigao / stigla
• budeš stigao / stigla
• bude stigao / stigla
• etc.

So budem is not random here; it is the auxiliary that helps create this future form.

Because the speaker is understood to be female.

The form stigla agrees with the gender of the subject:

• stigao = masculine singular
• stigla = feminine singular
• stigli = masculine/mixed plural
• stigle = feminine plural

So:

• a woman says Kada budem stigla...
• a man says Kada budem stigao...

This is a very common feature of Serbian past-participle-based forms.

Yes. That is very common and natural.

So both of these can work:

• Kada budem stigla na aerodrom...
• Kad stignem na aerodrom...

The version with budem stigla is a bit more explicit about the action being completed before the next one. The version with stignem is often more conversational and very common in everyday speech.

A learner should recognize both.

Because Serbian normally uses na with certain places seen as functional locations or public spaces, and aerodrom is one of them.

So:

• ići na aerodrom = to go to the airport
• biti na aerodromu = to be at the airport

This is similar to other expressions like:

• na stanicu
• na fakultet
• na pijacu

Using u aerodrom would usually sound unnatural unless you meant something very literal like going inside a specific building space, and even then Serbian would usually phrase it differently.

Because this is the standard Serbian way of writing future I when the infinitive comes before the auxiliary.

Compare:

• Ja ću proveriti.
• Proveriću.

In proveriću, the infinitive stem joins with the clitic ću.

So:

• proveriti + ću → proveriću

This is normal in Serbian spelling.

Also, clitics like ću usually cannot stand in first position by themselves, so if there is no separate word before them, Serbian often uses this joined form.

Da li introduces an indirect yes/no question.

So:

• proveriću da li moj let kasni
• = I will check whether / if my flight is late

This is important because English if has two meanings:

1. whether
2. on the condition that

In Serbian, those are usually separated more clearly:

• da li = whether
• ako = if in the conditional sense

So here da li is correct because the meaning is whether my flight is late, not if my flight is late, then...

Because kasni here describes the flight’s status: is it delayed / is it running late?

Even though the checking will happen in the future, Serbian naturally uses the present tense in this kind of indirect question to express the flight’s condition at that time.

So:

• da li moj let kasni = whether my flight is late / delayed

You could also hear da li će moj let kasniti, but that sounds more like asking about a future prediction: whether my flight will be late.

The version with kasni is very natural when talking about delay status.

The verbs are:

• stići — perfective
• proveriti — perfective
• kasniti — imperfective

Why that makes sense:

• stići = to arrive, a completed event
• proveriti = to check once, a completed action
• kasniti = to be late / to run late, an ongoing state or process

So the sentence combines:

• one completed future event: budem stigla
• another completed future action: proveriću
• one ongoing condition: let kasni

This is a very typical Serbian aspect pattern.

The word order can change somewhat, because Serbian is fairly flexible, but the given version is very natural:

• Kada budem stigla na aerodrom, proveriću da li moj let kasni.

This order is clear because it goes:

1. time clause
2. main action
3. indirect question

You can move things around in Serbian, but not every rearrangement sounds equally natural. For learners, the safest option is to keep the sentence in this order.

Also note that the comma after the first clause is standard, because Kada budem stigla na aerodrom is a subordinate clause placed before the main clause.

They both mean when.

• kada = full form
• kad = shorter form, very common in everyday speech and writing

So both are fine:

• Kada budem stigla...
• Kad budem stigla...

In many situations, kad sounds a bit more conversational, while kada can sound slightly fuller or more careful. But the difference is small, and both are normal Serbian.