modality - Subject + am/is/are + to + verb

Could anybody clear it to me whether these two sentence are grammatically equal? If not, what is the difference?

1) They must use some methods...
2) They are to use some methods...

Answer

The modal verb must in this sentence denotes that using some methods is completely necessary or very important.

On the other hand, are to talks about their likelihood to use some methods.

This said,

They must use some methods - they should use some methods, it's utterly necessary.

and...

The are to use some methods - it's likely that they will use some methods.