During the safety briefing on the 744 on UA, the following announcement is made. I don’t know if NW does it, but I would assume they say something similar.
For customers in the upper deck, in a water evacuation, your primary emergency exit is down the stairs and out one of the main deck exits...For customers sitting in the upper deck, in a land evacuation your primary emergency exit is out the upper deck.
Does anyone know what Airbus plans to do on the A380 for a water evacuation? I assume the slides will still be too step to make it possible to have a raft at the bottom, but I doubt only the main deck exits will be capable of evacuating both decks in under ninety seconds. Obviously, I understand that a "water evacuation" is a misnomer, but I am asking this question from a regulatory standpoint, not from a practical one.