How to differentiate between multiple meanings of "devoir"?

Question

Please correct me if I'm wrong, as per my understanding:

"Devoir" has multiple meanings, usually depending on the context; it can either be (literal or figurative) debt, obligation, or probability. It's also usually translated to 'must' or 'to have to'.

With that being said, consider the following sentence:

L'avion doit atterrir à dix heures.

How can one tell if it can be translated as:

The plane is supposed to land at ten o'clock. (probability)

or

The plane must land at ten o'clock. (literal translation)

Answer 1

The context will allow to choose between the possible meanings.
In your example, both translations could be possible, but given the context, only one would suit.

Without any additional information, your example would be understood as 'the plane is supposed to land at ten o'clock', and that's what is planned.

Another example where we would instead choose the second meaning:
L'avion doit atterrir à dix heure ou il perdra son créneau. -> The plane must land at ten o'clock or it will lose its slot.

As you can see, the context allows us to choose the suitable meaning. If there is no context, usually it can be inferred from the common use of the sentence.

Answer 2

It depends on context.

Si l'on veut arriver à l'heure pour le déjeuner, l'avion doit atterrir à dix heures.

⇒ The plane must land at ten o'clock

Tu peux venir me chercher à l'aéroport ? L'avion doit atterrir à dix heures...

⇒ The plane is supposed to land at ten o'clock

J'ai bien étudié les temps de parcours. L'avion DEVRAIT atterrir à dix heures.

⇒ probability