Посадка была мягкой, и мне стало спокойнее.

Here посадка means landing, most likely an airplane landing from the context.

This noun can mean different things in other contexts, for example:

• посадка на поезд — boarding a train
• посадка деревьев — planting trees
• посадка пассажиров — seating/boarding passengers

So this is a good example of a Russian noun whose exact meaning depends on context.

Because посадка is a feminine singular noun.

In the past tense, Russian verbs agree with the subject in gender and number:

• он был — he was
• она была — she/it was
• оно было — it was
• они были — they were

So:

• посадка была = the landing was

Because after быть in the past tense, Russian often uses the instrumental case for the predicate adjective.

So:

• Посадка была мягкой = The landing was smooth/soft

This is very natural and standard Russian.

You may sometimes hear or see мягкая in similar structures, especially in more colloquial speech, but мягкой is the safer form to learn here.

A useful pattern is:

• Он был усталым — He was tired
• Она была счастливой — She was happy
• Посадка была мягкой — The landing was smooth

Literally, it is something like:

to me it became calmer

That sounds odd in English, but it is a very normal Russian way to express a change in someone’s internal state.

Breakdown:

• мне — to me
• стало — became
• спокойнее — calmer

So natural English translations are:

• I felt calmer
• I became calmer
• I felt more at ease

Because Russian often uses the dative for the person who experiences a feeling or state.

This is common in expressions like:

• мне холодно — I am cold
• мне грустно — I am sad
• мне стало лучше — I felt better
• мне стало спокойнее — I felt calmer

So Russian is not phrasing this as I did something, but rather as a state happened to me.

Because this is an impersonal construction.

There is no explicit grammatical subject like я in the sentence мне стало спокойнее. In these impersonal expressions, Russian typically uses neuter singular past tense:

• стало
• было

That is why you get:

• мне стало легче
• ему стало плохо
• нам стало весело

Even though the meaning refers to a real person, the grammar is impersonal.

Спокойнее is the comparative form of спокойный / спокойно.

It means:

• calmer
• more calm
• more at ease

A very important point: this comparative form is invariable here. It does not change for gender, number, or case.

Compare:

• спокойный — calm
• спокойная — calm (feminine)
• спокойное — calm (neuter)
• спокойнее — calmer

So after стало, you use спокойнее, not a gendered adjective form.

Because стало shows a change of state.

• мне стало спокойнее = I became calmer / I started to feel calmer
• мне было спокойнее = I felt calmer / I was calmer

In this sentence, the idea is that the smooth landing caused a change: before the landing, the speaker was more nervous; after it, the speaker felt calmer. That is exactly why стало fits so well.

Yes, you could.

• Я стал спокойнее — I became calmer
• Мне стало спокойнее — I felt calmer / It became calmer for me

Both are possible, but they are not identical in feel.

Я стал спокойнее is more direct and personal: it focuses on I as the subject.

Мне стало спокойнее is more natural for describing an internal feeling or emotional shift. Russian often prefers this kind of impersonal wording for states and sensations.

Because и is joining two independent clauses, each with its own verb:

• Посадка была мягкой
• мне стало спокойнее

Since each part can stand as its own clause, Russian puts a comma before и here.

So the structure is:

[clause 1], и [clause 2]