Стюардесса сказала, что самолёт скоро сядет.

Because Russian past-tense verbs agree with the gender of the subject.

The subject here is стюардесса, which is feminine, so the verb is сказала.

Compare:

• стюард сказал = the male flight attendant said
• стюардесса сказала = the female flight attendant said

In the past tense:

• masculine: сказал
• feminine: сказала
• neuter: сказало
• plural: сказали

Because что introduces a subordinate clause.

Russian normally puts a comma before что in sentences like this:

• Она сказала, что...
• Я думаю, что...
• Мы знаем, что...

So Стюардесса сказала, что самолёт скоро сядет is literally structured as:

The flight attendant said, that the plane will land soon

Even though English often omits that, Russian usually keeps что here and marks the clause boundary with a comma.

Russian does not usually do the same kind of tense backshifting that English does.

In English, after a past verb like said, you often shift the next verb back:

• She said the plane would land soon

In Russian, if the landing is still in the future from the point of view of the original statement, Russian simply uses the future:

• сказала, что самолёт скоро сядет

So this is completely normal Russian. It does not sound strange or inconsistent.

Yes. Сесть literally means to sit down, but it also has several extended meanings.

For vehicles, especially planes, сесть can mean to land.

So:

• самолёт сядет = the plane will land

This is a very common and natural way to say it.

The verb сядет is the future form of the perfective verb сесть.

Yes. Самолёт скоро приземлится is also correct and very common.

The difference is roughly this:

• сядет = literally will sit down, idiomatically will land
• приземлится = will land / touch down, more directly tied to landing

Both are natural.
Самолёт скоро сядет sounds very normal in everyday speech.

Because самолёт is the subject of the subordinate clause, so it is in the nominative case.

In что самолёт скоро сядет:

• самолёт = subject
• сядет = verb

So no special case ending is needed here.

Скоро means soon.

In this sentence it modifies сядет:

• самолёт скоро сядет = the plane will land soon

Its position can change, although the most neutral version here is the original one.

For example:

• Стюардесса сказала, что самолёт скоро сядет
• Стюардесса сказала, что скоро самолёт сядет

Both are possible, but the first one is more standard and natural in this context.

In standard speech, что is very often pronounced closer to што.

So learners often hear:

• что → што

This is normal and not sloppy. It is the usual pronunciation for this very common word.

Yes, it is helpful because ё shows both the sound and the stress.

Самолёт is stressed on the last syllable:

• са-мо-лёт

That helps you pronounce it correctly.

In many printed texts, Russian writers omit the dots and write е instead of ё, so you may often see самолет. But the word is still pronounced самолёт.

Yes, стюардесса is widely understood and still common, especially in everyday speech.

However, you may also hear or see:

• бортпроводница = a more official or formal word for a female flight attendant
• бортпроводник = a male flight attendant

So стюардесса сказала... is perfectly natural, but in airline announcements or official contexts, бортпроводница may sound more formal.

Yes. Russian word order is flexible, though not completely free.

The sentence:

• Стюардесса сказала, что самолёт скоро сядет

is the most neutral way to say it.

Other orders are possible for emphasis, for example:

• Стюардесса сказала, что скоро самолёт сядет
• Что самолёт скоро сядет, стюардесса сказала

But these sound more marked or context-dependent. For a learner, the original order is the safest and most natural choice.