Learn Spanish (Latin America): El avión había aterrizado en Chile para la escala. - The plane had landed in Chile for the layover.

Había aterrizado is the past perfect tense. We use it to emphasize that this action was completed before another past event. Even though the second event isn't mentioned here, using había implies a timeline like 'The plane had landed... by the time I woke up.'

Why use para instead of por in para la escala?

We use para here because it expresses purpose or intention. The specific goal of the landing was the layover (la escala).

Will the ending of aterrizado ever change depending on what is landing?

Not in this structure. When a past participle like aterrizado is used with any form of the helping verb haber (like había), it always ends in -o. It does not change to match gender or number.

Does escala always mean 'layover'?

In the context of travel, yes, una escala is a flight connection, layover, or stopover. However, in other contexts it can mean 'scale' (like a musical scale or a map's scale).