Learn Hardcore Japanese: hikouki no tiketto ni ha, tuurogawa ka madogawa ka ga purintaa de kirei ni insatusite arimasu. - On the airplane ticket, whether it's an aisle or window seat is neatly printed by the printer.

チケットに (without は) would simply state the location:
チケットに通路側か窓側かが印刷してあります。
“(Something) is printed on the ticket.”
Grammatically OK, but it feels more like a bare factual description.
チケットは (without に) would mean “As for the ticket, …” but loses the clear idea of “on the ticket”. You’d usually still want に to show “where” it is printed.

So チケットには nicely does both jobs at once:
“It is on the ticket that (X) is neatly printed.”

Why is か used twice in 通路側か窓側か?

Here, 通路側か窓側か forms an embedded “whether A or B” question:

AかBか = “whether A or B”

So 通路側か窓側か means “whether (the seat is) aisle side or window side”.

Compare:

通路側か窓側かが印刷してあります。
→ “(The fact of) whether it’s aisle or window is printed.”
通路側か窓側が印刷してあります。
→ Sounds like “aisle side or window side (one of them) is printed”, which is odd.

That second か tells the reader, “I’m closing off this ‘whether A or B’ chunk now; the whole chunk is one unit.” It’s similar to English “whether A or B is printed…”

What’s going on with 通路側か窓側かが? How can か and が appear together?

Break it into parts:

通路側か窓側か = “whether (it is) aisle side or window side”
が = subject marker

So the structure is:

[通路側か窓側か] が印刷してあります。
“The fact of whether it’s aisle or window is printed.”

The entire bracketed part is the subject of 印刷してあります.

This is very similar to the pattern:

〜かどうかが分かりません。
“(I) don’t know whether ~ or not.”

So かが is just “(embedded question) + が”, not a single particle.

Why is it プリンターで and not プリンターに or something else?

で after a noun often means “by / with / using (as a means or tool)”.

プリンターで印刷する
= “to print with a printer / by printer”

So プリンターで here means “by (using a) printer”, i.e. mechanically printed.

If you used に, it would sound like you’re locating something “at the printer” rather than using it as a tool, which doesn’t fit.

Other examples of で as “by/with”:

手で書く – write by hand
車で行く – go by car
パソコンでメールを送る – send email by computer

What exactly is きれいに doing here? Why not きれいな?

きれい is a na-adjective.
Na-adjectives form adverbs by adding に:

きれい (clean / pretty / neat) → きれいに (neatly, cleanly, beautifully)

In this sentence:

きれいに modifies the verb phrase 印刷してあります
→ “is neatly printed”

You’d use きれいな before a noun:

きれいな字 – neat handwriting
きれいなチケット – a clean/pretty ticket

But before a verb, you need the adverb form きれいに.

What does 印刷してあります mean, and how is 〜てある used?

印刷してあります is:

印刷する – to print
印刷してある – “has been printed (and remains that way)”

The pattern 〜てある describes:

A deliberate action done by someone, and
The resulting state that still exists now.

So:

通路側か窓側かがプリンターできれいに印刷してあります。
→ “Whether it’s aisle or window has been (deliberately) printed neatly by a printer, and it’s there now.”

Other examples:

ドアが開けてあります。
Someone has opened the door, and it’s now (intentionally) left open.
テーブルの上にコップが置いてあります。
Someone has put a cup on the table, and it’s there now.

So the sentence emphasizes the resulting, prepared state of the ticket: the information is already neatly printed on it.

What’s the difference between 印刷してあります and 印刷されています?

Both can translate as “(is) printed”, but the nuance differs:

印刷してあります (〜てある)
- Focus: someone intentionally did the action, and the result remains.
- Implies “it has been printed (for a purpose), and it’s in that prepared state”.
印刷されています (〜ている passive)
- Focus: the state or ongoing result; agent is less important.
- More neutral “is printed / is being printed / is in a printed state”.

In context of tickets, you’d typically use:

〜が印刷してあります。
→ Sounds like: “They’ve printed X on the ticket for you; it’s all set.”

印刷されています could work, but sounds a bit more like a general description of how things are, rather than stressing that it’s been prepared for you.

Why do we just say 通路側 and 窓側, without 席 (seat)?

In airline context, 通路側 and 窓側 almost automatically mean:

通路側（の席） – aisle seat
窓側（の席） – window seat

Japanese often omits words that are obvious from context. Since we’re talking about 飛行機のチケット, it’s clear we’re talking about seat type, not literally “aisle-side” or “window-side” with no noun.

You could say:

通路側の席か窓側の席かが印刷してあります。

This is grammatically fine, just a bit heavier; everyday Japanese tends to drop the second 席 (and often the first, too).

Can the word order be changed, like putting 飛行機のチケットには later in the sentence?

Japanese word order is somewhat flexible, but topics usually appear early.

Your sentence:

飛行機のチケットには、通路側か窓側かがプリンターできれいに印刷してあります。

Other possible (still natural) orders:

飛行機のチケットには、通路側か窓側かがきれいにプリンターで印刷してあります。
(Just moving プリンターで a bit.)

You could move 飛行機のチケットには later:

通路側か窓側かが、飛行機のチケットにはプリンターできれいに印刷してあります。

This is grammatically OK, but sounds a bit less natural because the topic phrase usually comes first in ordinary explanations. Keeping 飛行機のチケットには at the start is the most typical, neutral order here.

Why is it 飛行機のチケット and not something like 飛行機チケット?

飛行機のチケット uses の to link two nouns:

飛行機 – airplane
チケット – ticket
飛行機のチケット – airplane ticket / plane ticket

This の is similar to English “of” or the noun-noun connection in “plane ticket”.

Japanese sometimes makes direct noun–noun compounds (like 新幹線チケット does appear), but:

飛行機のチケット is the normal, standard expression.
飛行機チケット is understandable but sounds more like a shortened, casual or advertising-style phrase than standard everyday Japanese.

So for ordinary sentences, 飛行機のチケット is the natural choice.