hikouki ga buzi ni kuukou ni tuita to kiite, ansinsimasita.

が marks 飛行機 as the subject of 着いた.

So the core part is:

• 飛行機が着いた = the plane arrived

Using が sounds natural here because the sentence is reporting a specific event: the plane’s safe arrival.

If you used は instead, it would sound more like you are setting the plane up as the topic and then saying something about it. That is possible in some contexts, but が is the most straightforward choice for this sentence.

無事 means safety, without problems, or safely depending on context.

In this sentence, 無事に means:

• safely
• without incident
• all right

The に turns 無事 into an adverb-like expression modifying the verb 着いた.

So:

• 無事に着いた = arrived safely

This is very common in Japanese:

• 静かに話す = speak quietly
• きれいに書く = write neatly
• 無事に終わる = end safely / without problems

They do different jobs.

1. 無事に
   This に makes 無事 function adverbially:

   • 無事に = safely

2. 空港に
   This に marks the destination of 着いた:

   • 空港に着いた = arrived at the airport

So the sentence contains:

• 無事に = safely
• 空港に = at/to the airport

Same particle, different functions.

Because 着いた appears before と聞いて, and before と in this kind of quotation/reporting structure, Japanese usually uses the plain form.

So:

• 飛行機が無事に空港に着いた = the plane arrived safely at the airport
• 〜と聞いて = hearing that / having heard that

This is a very important pattern:

• 彼が来ると聞いた = I heard that he is coming
• 試験が難しかったと聞いた = I heard that the exam was difficult

Even in polite sentences overall, the quoted content is often in plain form.

Here, と marks the content of what was heard.

So:

• 飛行機が無事に空港に着いた = the plane arrived safely at the airport
• と聞いて = hearing that

Together:

• 飛行機が無事に空港に着いたと聞いて = hearing that the plane arrived safely at the airport

You can think of と here as something like that in English:

• I heard that the plane arrived safely.

This use of と is extremely common with verbs like:

• 言う = say
• 思う = think
• 知る = learn/find out
• 聞く = hear

The て-form connects this action to the next part of the sentence.

Here it means something like:

• after hearing that
• having heard that
• when I heard that

So the structure is:

• 〜と聞いて、安心しました。
• I heard that 〜, and I felt relieved.

The て-form often connects actions in sequence or shows a reason/background.

In this sentence, it gives the reason for the relief:

• Because I heard the plane arrived safely, I felt relieved.

Yes, 安心 is basically a noun meaning relief or peace of mind.

But Japanese often makes these nouns into verbs by adding する:

• 安心する = to feel relieved / to be relieved

So:

• 安心しました = felt relieved

This is a very common pattern:

• 勉強する = study
• 心配する = worry
• 予約する = make a reservation
• 安心する = feel relieved

The person who felt relieved is omitted because Japanese often leaves out information that is understood from context.

So 安心しました most naturally means:

• I felt relieved

But depending on context, it could also mean:

• we felt relieved
• he/she felt relieved

In many standalone textbook sentences, the default interpretation is usually I.

Japanese very often omits subjects when they are obvious or not important to state directly.

It can feel like either, depending on context.

Literally, 聞く means to hear or to ask, but in sentences like this:

• 〜と聞いて

it often means:

• hearing that
• being told that
• learning that
• finding out that

So the nuance is not necessarily that the speaker physically heard a sound. It often just means they received that information somehow.

With 着く, the destination is normally marked by に.

So:

• 空港に着く = arrive at the airport

Using へ with 着く is much less standard. へ emphasizes direction, while 着く is about reaching a destination, so に fits better.

Compare:

• 空港へ行く = go to the airport
• 空港に着く = arrive at the airport

Yes. The て-form here is flexible, so several English translations are possible depending on what sounds natural:

• When I heard that the plane had arrived safely at the airport, I felt relieved.
• After hearing that the plane had arrived safely at the airport, I felt relieved.
• I felt relieved when I heard that the plane had arrived safely at the airport.
• Hearing that the plane had arrived safely at the airport, I felt relieved.

All of these capture the Japanese well.

Japanese often leaves the exact relationship slightly broad, and English chooses the version that sounds most natural in context.