Перед посадкой я всегда проверяю посадочный талон ещё раз.

Because перед normally takes the instrumental case when it means before or in front of something.

So:

• посадка = boarding
• instrumental singular = посадкой

That gives:

• перед посадкой = before boarding

This is a very common pattern:

• перед уроком = before the lesson
• перед встречей = before the meeting
• перед вылетом = before departure

So the ending -ой on посадкой shows the instrumental case.

It can mean either, depending on context.

• посадка в самолёт = boarding a plane
• посадка самолёта = the plane’s landing

In this sentence, it clearly means boarding, because of посадочный талон (boarding pass). Those two words naturally go together in airport language.

So:

• Перед посадкой here = Before boarding

Посадочный is an adjective formed from посадка. It means something like for boarding or related to boarding.

So:

• талон = pass/slip/coupon
• посадочный талон = boarding pass

This is the standard Russian expression for boarding pass.

A learner might expect something more literal like билет, but билет is usually ticket, not specifically the document you show when boarding. At the airport, посадочный талон is the normal term.

Because Russian uses the present tense for habitual or regular actions, just like English does in sentences such as I always check.

So:

• я всегда проверяю = I always check

It does not mean only I am checking right now. In this context it means a repeated habit.

Also, проверяю is imperfective, which fits well with repeated actions:

• проверять / проверить = to check

Here, the imperfective проверяю is natural because the speaker is describing what they generally do every time.

It is in the accusative case, because it is the direct object of проверяю (I check).

• проверяю что? → посадочный талон

However, for an inanimate masculine singular noun, the accusative looks the same as the nominative.

So:

• nominative: посадочный талон
• accusative: посадочный талон

That is why the form does not change here.

Ещё раз means one more time or again.

In this sentence:

• проверяю посадочный талон ещё раз = I check my boarding pass one more time

It suggests a repeated check, often for safety or certainty.

A useful nuance:

• ещё раз = one more time / once again
• снова or опять = again

In many cases they overlap, but ещё раз emphasizes the idea of an additional repetition. Here that works very well: the speaker checks it once more before boarding.

Yes, but the nuance changes a little.

• ещё раз = one more time
• снова = again
• опять = again, often with a feeling like yet again

In this sentence, ещё раз sounds especially natural because checking a boarding pass is a small repeated action done once more before boarding.

Compare:

• Я всегда проверяю посадочный талон ещё раз.
  = I always check my boarding pass one more time.

• Я всегда снова проверяю посадочный талон.
  Grammatically possible, but less natural here.

• Я всегда опять проверяю посадочный талон.
  Can sound like I end up checking it again, sometimes with a hint of annoyance.

So ещё раз is the best choice in this sentence.

Not always. Russian often drops subject pronouns when they are clear from the verb.

So you could also say:

• Перед посадкой всегда проверяю посадочный талон ещё раз.

This still means Before boarding, I always check my boarding pass one more time, because проверяю already shows I.

Why include я, then?

• for clarity
• for emphasis
• because it sounds natural in many full sentences

So я is optional here, but perfectly normal.

Russian word order is flexible, and всегда can move around depending on emphasis.

In the given sentence:

• Перед посадкой я всегда проверяю посадочный талон ещё раз.

This sounds neutral and natural.

You could also hear:

• Я всегда перед посадкой проверяю посадочный талон ещё раз.
• Я перед посадкой всегда проверяю посадочный талон ещё раз.

These are all understandable, but the original order is very smooth and standard.

In general:

• the meaning stays the same
• the word order changes the focus or rhythm, not the basic grammar

Yes, до посадки is possible and also means before boarding, but there is a slight difference in feel.

• перед посадкой = before boarding, often right before it
• до посадки = before boarding, more generally before that point in time

So:

• Перед посадкой я всегда проверяю посадочный талон ещё раз.
  sounds very natural for something done shortly before boarding.

• До посадки я всегда проверяю посадочный талон ещё раз.
  is also understandable, but slightly less idiomatic in this exact context.

For airport routines, перед посадкой is an excellent choice.

It actually does match the noun, just in a way that may not be very visible if you are new to Russian.

In посадочный талон:

• талон is masculine singular
• посадочный must also be masculine singular
• the whole phrase is accusative, but because талон is inanimate, accusative = nominative

So the phrase stays:

• посадочный талон

If the noun changed, the adjective would change too. For example:

• перед посадкой — here посадкой is feminine instrumental
• if there were an adjective with it, that adjective would also be feminine instrumental

Russian adjectives always agree with the noun in:

• gender
• number
• case

A close natural translation would be:

• Before boarding, I always check my boarding pass one more time.

Other natural versions:

• I always check my boarding pass again before boarding.
• Before boarding, I always double-check my boarding pass.

That last version, double-check, captures the idea of ещё раз very well, even though it is not a word-for-word translation.