Planen ändras om tåget är försenat.

Because planen is the definite singular form: the plan.

• en plan = a plan
• planen = the plan

Swedish usually adds the definite ending to the noun itself, instead of putting a separate word like the in front.

Ändras means is changed or changes, depending on how naturally you want to translate it.

In this sentence, it is an -s passive form of the verb ändra:

• ändra = to change something
• ändras = to be changed

So:

• Planen ändras = The plan is changed / The plan changes

In English, is changed is often the clearest way to understand the grammar.

Swedish often uses the -s passive where English uses be + past participle.

So instead of:

• är ändrad = is changed

Swedish very naturally says:

• ändras = is changed

Both kinds of forms exist in Swedish, but the -s passive is very common, especially in general statements like this one.

Yes. Ändras is present tense passive.

A helpful comparison:

• ändrar = changes / is changing
• ändras = is changed
• ändrades = was changed
• har ändrats = has been changed

So in Planen ändras om tåget är försenat, the sense is The plan is changed if the train is delayed.

Because tåget means the train.

• ett tåg = a train
• tåget = the train

Tåg is a neuter noun (ett noun), so its definite singular ending is -et.

Because försenat agrees with tåget, and tåget is a neuter noun (ett tåg).

Compare:

• en buss är försenad = a/the bus is delayed
• ett tåg är försenat = a/the train is delayed

So the adjective changes form to match the noun's gender.

Because försenat specifically means delayed, which fits trains very naturally.

• tåget är försenat = the train is delayed
• tåget är sent can be understood, but försenat is the more standard and idiomatic choice for transport.

So this is the normal way to say that a train is running late.

Yes. In this sentence, om means if.

• om tåget är försenat = if the train is delayed

This is important because om can also mean about in other contexts:

• en bok om Sverige = a book about Sweden

So the meaning depends on context. Here it is clearly the conditional if.

Because in a subordinate clause introduced by om (if), Swedish normally keeps the subject before the verb:

• tåget är försenat
• om tåget är försenat

So:

• om = subordinator
• tåget = subject
• är = verb
• försenat = adjective/complement

This is normal Swedish subordinate-clause word order.

Yes, absolutely.

Both of these are correct:

• Planen ändras om tåget är försenat.
• Om tåget är försenat ändras planen.

The meaning is the same. The only difference is what comes first.

Notice that when the om-clause comes first, the main clause still follows normal Swedish V2 word order:

• Om tåget är försenat, ändras planen.

That is why you get ändras planen, not planen ändras, after the opening clause.

Sometimes, yes. Planen can mean:

• the plan
• the field/pitch/court in some contexts

But in this sentence, with ändras (is changed), the meaning is clearly the plan. A field or pitch would not normally be changed in this way.

So context makes the meaning clear.

Sometimes, but it means something slightly different.

• är försenat = is delayed (the state)
• blir försenat = becomes delayed / gets delayed (the change into that state)

So:

• om tåget är försenat = if the train is delayed
• om tåget blir försenat = if the train gets delayed

Both are possible, but är försenat is the most straightforward form in this sentence.