Προτιμώ απευθείας πτήση, γιατί δεν μου αρέσει να αλλάζω αεροπλάνο.

Προτιμώ means I prefer. It is the 1st person singular present tense of the verb προτιμώ.

So:

• προτιμώ = I prefer
• προτιμάς = you prefer
• προτιμά = he/she/it prefers

In this sentence, the speaker is saying what they generally prefer, so the present tense is the natural choice.

Here απευθείας means direct or non-stop.

In απευθείας πτήση, it works like an indeclinable modifier, meaning it stays the same and does not change for gender, number, or case.

So unlike many Greek adjectives, it does not have different endings. You can think of it as a fixed word meaning direct in travel contexts.

Examples:

• απευθείας πτήση = direct flight
• απευθείας σύνδεση = direct connection
• απευθείας μετάδοση = live/direct broadcast

Greek often leaves out the article when talking about something in a general or indefinite way.

So:

• Προτιμώ απευθείας πτήση = I prefer a direct flight

This sounds natural when speaking generally about one’s preference.

You could also say:

• Προτιμώ μια απευθείας πτήση

This also means I prefer a direct flight, but μια makes the noun a little more explicitly a/an.

πτήση is in the accusative singular, because it is the direct object of Προτιμώ.

The basic dictionary form is η πτήση = the flight.
Its singular forms are:

• nominative: η πτήση
• genitive: της πτήσης
• accusative: την πτήση

After προτιμώ, Greek uses the accusative:

• Προτιμώ την πτήση
• Προτιμώ απευθείας πτήση

In everyday speech, feminine nouns like this often look the same in nominative and accusative except for the article.

Greek uses αρέσει differently from English like.

Literally, μου αρέσει is closer to:

• it is pleasing to me
• it appeals to me

So:

• μου = to me
• αρέσει = pleases / is pleasing

That is why Greek says:

• Μου αρέσει ο καφές = I like coffee
  literally: Coffee is pleasing to me

And here:

• δεν μου αρέσει να αλλάζω αεροπλάνο = I don’t like changing planes

So the thing that is disliked is the whole action να αλλάζω αεροπλάνο.

μου is the weak form of the pronoun meaning to me / my, depending on context.

Here it means to me:

• δεν μου αρέσει = it is not pleasing to me = I don’t like it

This is an indirect object pronoun.

Compare:

• μου αρέσει = I like
• σου αρέσει = you like
• του αρέσει / της αρέσει = he/she likes
• μας αρέσει = we like

This is a very common question, because Greek distinguishes between imperfective and perfective verb forms after να.

• να αλλάζω = to be changing / to change in general / repeatedly
• να αλλάξω = to change once / to complete the change

In this sentence, the speaker means they do not like the process or general experience of changing planes, so να αλλάζω is the natural choice.

So:

• δεν μου αρέσει να αλλάζω αεροπλάνο = I don’t like changing planes

If you used να αλλάξω, it would sound more like a specific single instance:

• Δεν θέλω να αλλάξω αεροπλάνο αύριο = I don’t want to change planes tomorrow

να is a very common Greek particle used before verb forms that correspond to things like:

• to do
• that I do
• in order to do
• various subjunctive-like meanings

After expressions such as μου αρέσει or δεν μου αρέσει, Greek usually uses να + verb to talk about an action.

So:

• Μου αρέσει να ταξιδεύω = I like to travel
• Δεν μου αρέσει να περιμένω = I don’t like to wait
• Δεν μου αρέσει να αλλάζω αεροπλάνο = I don’t like changing planes

In English, you might use either to change planes or changing planes. Greek uses να + verb.

Literally, it means I change airplane.

But in natural English, the meaning is:

• to change planes
• to transfer to another plane

Greek often expresses this idea with:

• αλλάζω αεροπλάνο

This is a standard and natural way to talk about flight connections.

Because the sentence is talking about the activity in general, not a specific plane.

So:

• να αλλάζω αεροπλάνο = to change planes

This is similar to how English also often avoids an article in general expressions.

If you added an article, it would point more to a specific plane, which is not the idea here.

Yes. A few natural alternatives are possible, depending on style and context.

For example:

• Προτιμώ απευθείας πτήσεις, γιατί δεν μου αρέσει να αλλάζω αεροπλάνο.
  = I prefer direct flights, because I don’t like changing planes.

• Προτιμώ πτήση χωρίς ανταπόκριση.
  = I prefer a flight without a connection.

• Προτιμώ να πετάω απευθείας.
  = I prefer to fly direct.

Your original sentence is completely natural and clear.

γιατί means because here.

It introduces the reason:

• Προτιμώ απευθείας πτήση = I prefer a direct flight
• γιατί δεν μου αρέσει να αλλάζω αεροπλάνο = because I don’t like changing planes

Be aware that γιατί can also mean why in questions:

• Γιατί προτιμάς απευθείας πτήση; = Why do you prefer a direct flight?

So the same word can mean either because or why, depending on the sentence.

No, Greek word order is more flexible than English word order, although some orders sound more natural than others.

The given sentence is very natural:

• Προτιμώ απευθείας πτήση, γιατί δεν μου αρέσει να αλλάζω αεροπλάνο.

You could also hear slight variations, such as:

• Γιατί δεν μου αρέσει να αλλάζω αεροπλάνο, προτιμώ απευθείας πτήση.

But this sounds more marked, because it puts the reason first.

So the original order is the most straightforward and neutral one for everyday use.