Helicopters can be landed softly without power, via autorotation. It's not hard to imagine an autonomous helicopter that can manage autorotations. Some drones

Helicopters can be landed softly without power, via autorotation. It's not hard to imagine an autonomous helicopter that can manage autorotations. Some drones already do. But for people-carrying operations, it would need to have an extremely fine-grained terrain database (better than we probably have today) to pick suitable landing spots and avoid low-level obstacles.