Me gusta mirar por la ventana cuando el avión empieza a despegar.

Because gustar works differently from to like in English.

In Spanish, gustar literally works more like to be pleasing to. So:

• Me gusta mirar por la ventana = Looking out the window is pleasing to me
• not I like in the literal English structure

So:

• me = to me
• gusta = is pleasing

You use yo gusto only in a very different sense, like I am pleasing / attractive, which is not what this sentence means.

Because the thing being liked is treated as a singular idea: mirar por la ventana cuando el avión empieza a despegar.

In Spanish, when gustar is followed by an infinitive, the infinitive acts like a singular subject, so you use gusta, not gustan.

Examples:

• Me gusta leer. = I like reading.
• Me gusta viajar. = I like travelling.
• Me gusta mirar por la ventana... = I like looking out the window...

You would use gustan with a plural noun:

• Me gustan los libros. = I like books.

After gustar, if you want to say you like doing something, Spanish uses the infinitive.

So:

• Me gusta mirar... = I like to look / I like looking...
• not Me gusta miro...

This is similar to saying:

• Me gusta comer
• Me gusta nadar
• Me gusta estudiar

The verb after gusta stays in the infinitive form.

Both can relate to sight, but they are not exactly the same.

• ver = to see
• mirar = to look / to watch

In this sentence, mirar por la ventana suggests the deliberate action of looking out the window. That makes mirar the natural choice.

Compare:

• Veo la montaña. = I see the mountain.
• Miro por la ventana. = I look out the window.

So mirar fits better because the person is actively looking outside.

In Spanish, mirar por la ventana is the normal way to say to look out the window.

Here, por suggests looking through the window opening/glass.

Common expressions:

• mirar por la ventana = look out the window
• entrar por la puerta = come in through the door

If you said mirar a la ventana, that would usually sound more like look at the window itself, not through it.

And desde la ventana means from the window, which gives a different idea.

Spanish often uses the definite article (el, la, los, las) where English might not.

So por la ventana is the normal, natural expression:

• mirar por la ventana = look out the window

This does not necessarily mean a specific window that has already been mentioned. It is just how Spanish commonly phrases it.

This happens a lot in Spanish:

• Me duele la cabeza. = My head hurts.
• Abre la puerta. = Open the door.
• Mira por la ventana. = Look out the window.

Both are possible, but they are slightly different.

• cuando el avión despega = when the plane takes off
• cuando el avión empieza a despegar = when the plane starts to take off

The version with empieza a despegar focuses more on the beginning of the process, which matches the moment when many people like looking out the window.

So this sentence emphasizes the start of takeoff rather than the whole action in a more general way.

Because empezar is commonly followed by a + infinitive when it means to begin/start to do something.

So:

• empezar a + infinitive
• comenzar a + infinitive

Examples:

• Empiezo a trabajar a las ocho. = I start working at eight.
• El niño empieza a llorar. = The child starts to cry.
• El avión empieza a despegar. = The plane starts to take off.

That a is just part of the standard verb pattern.

Because Spanish often uses the present tense for general habits or things that are typically true.

This sentence means something like:

• I like looking out the window when the plane starts to take off

It is not talking about one specific flight only. It describes a usual preference or repeated experience.

So the present tense works naturally:

• Me gusta...
• cuando el avión empieza...

This is similar to English using the present in general statements:

• I like it when the movie starts.
• I relax when the train leaves.

Because el avión can be used in Spanish to talk about the plane involved in that situation in a general, natural way.

Here it does not have to mean one specially identified plane from earlier in the conversation. It can simply refer to the plane you are on / the plane in that context.

Using un avión would sound more like any plane or introduce a plane as a new, less specific item.

So:

• cuando el avión empieza a despegar = when the plane starts to take off
  feels natural in context
• cuando un avión empieza a despegar = when a plane starts to take off
  sounds more generic or detached

Yes. Despegar has several related meanings.

Its basic idea is something like to come unstuck / separate from a surface, and from that it also came to mean to take off for planes.

So:

• El avión despega. = The plane takes off.
• Despega la etiqueta. = Peel off the label.

This is very common in Spanish, and for flights despegar is the normal verb to use.

It would sound less natural.

The usual expression is mirar por la ventana because it means to look out the window, which is an intentional action.

Ver por la ventana is possible in some contexts, but it usually sounds more like to see through/out of the window, not specifically the act of looking out.

So for this sentence, mirar por la ventana is the best choice.

In Spanish, after cuando referring to habitual or general situations, the present tense is normal.

So:

• Me gusta mirar por la ventana cuando el avión empieza a despegar.

This means something that generally happens whenever that situation occurs.

Spanish does not use the future here the way English sometimes thinks about future time. The present tense is enough because it refers to a repeated circumstance, not a one-time prediction.

If you were talking about a specific future event, Spanish would often still avoid the simple future after cuando:

• Cuando el avión empiece a despegar, miraré por la ventana.

Here the verb after cuando becomes subjunctive because it refers to a specific future event.

So the original sentence is in the present because it describes a general habit or preference.