Inspired by this Q&A: How to handle falling down stairs?
Feather fall says:
Choose up to five falling creatures within range. A falling creature’s rate of descent slows to 60 feet per round until the spell ends. If the creature lands before the spell ends, it takes no falling damage and can land on its feet, and the spell ends for that creature.
It has a casting time of 1 Reaction:
which you take when you or a creature within 60 feet of you falls.
In my answer to the above Q&A, I document three (stair) cases where the characters can fall down stairs and take damage.
From Tales from the Yawning Portal:
From Rime of the Frostmaiden:
From Rise of Tiamat:
In the example from Yawning Portal the word "falls" is used to describe our descent of the stairs. In the latter two examples, the word "tumbles" and the phrase "sliding and tumbling" are used instead. As noted in my answer to the linked question, the module guidance for falling down stairs is very similar to the usual rules for falling.
Does feather fall work to prevent falling-down-stairs damage?