Ako avion sleti na vrijeme, stići ćemo na sastanak.

Because after ako (if), Croatian often uses the present tense to talk about a real future condition.

So:

• Ako avion sleti na vrijeme... = If the plane lands on time...
• not a separate future form inside the if clause

This is actually similar to English, which also says If the plane lands on time, not If the plane will land on time.

Sleti is the 3rd person singular verb form: he/she/it lands.

Here the subject is avion, which is singular, so the verb is also singular:

• avion sleti = the plane lands

This form comes from a perfective verb, so it suggests a single completed action: the plane successfully lands.

Because the sentence is talking about one completed event: the plane finishing its landing.

• sleti = lands / has landed successfully as a completed event
• slijeće = is landing / lands repeatedly, depending on context

In this sentence, the condition is completion of the landing. That is why the perfective form sleti is natural.

Croatian has no articles, so there is no direct equivalent of a/an/the.

So:

• avion can mean a plane or the plane
• sastanak can mean a meeting or the meeting

Context tells you which meaning is intended. In this sentence, it will usually be understood as the plane and the meeting, because both are probably known from the situation.

Because the verb already shows the subject.

• ćemo means we will
• so stići ćemo already means we will arrive / we’ll make it

Croatian often leaves subject pronouns out when they are not needed.

You could say Mi ćemo stići na sastanak, but that sounds more emphatic, like We will make it to the meeting.

Ćemo is the 1st person plural future auxiliary: we will.

So:

• stići ćemo = we will arrive / we will make it

This is the Croatian future tense built with:

• the infinitive: stići
• the auxiliary: ćemo

Because Croatian forms the future with an infinitive plus an auxiliary, and here they are written separately:

• stići = infinitive
• ćemo = auxiliary

Together they mean we will arrive.

This is just the normal way the future is built here.

They are similar, but not always identical.

• doći = to come / to arrive
• stići = to arrive / to reach / to make it

In this sentence, stići na sastanak sounds very natural because it suggests managing to get there in time.

So stići ćemo na sastanak is a bit like:

• we’ll arrive at the meeting
• we’ll make it to the meeting

Na vrijeme is a fixed expression meaning:

• on time
• sometimes in time, depending on context

Here it clearly means on time.

Even though na often means on/to, in this phrase you should learn na vrijeme as a whole expression.

Because na is commonly used with events or activities that you go to, such as:

• na sastanak = to a/the meeting
• na posao = to work
• na koncert = to a concert

So stići na sastanak is the normal Croatian way to say arrive at the meeting or make it to the meeting.

It is in the accusative singular: na sastanak.

That is because na takes the accusative when it shows movement toward a destination:

• ići na sastanak = to go to the meeting
• stići na sastanak = to arrive at the meeting

If you were talking about location rather than movement, Croatian often uses a different case pattern.

Avion is in the nominative singular, because it is the subject of the verb:

• avion sleti = the plane lands

The subject in Croatian is normally in the nominative.

Because the sentence begins with a conditional clause:

• Ako avion sleti na vrijeme, ...

Then the main clause follows:

• ... stići ćemo na sastanak.

So the comma separates the if-clause from the main clause when the conditional clause comes first.

Yes. You can also say:

• Stići ćemo na sastanak ako avion sleti na vrijeme.

That means the same thing.

Croatian word order is fairly flexible, but the original version is very natural because it presents the condition first and then the result.

It expresses a real possibility/condition.

It means:

• if this condition is met, that result will happen

So it is not purely hypothetical or impossible. It sounds like a normal, realistic future condition.

That is exactly why Croatian uses ako + present in the first clause and the future in the second.