The bird species that can amazingly stay in the air for 4 years and longer without landing is Albatross.
The Albatross bird is a master of soaring through the air without landing for over 4 years when needed and they are able to glide over vast tracts of ocean without flapping their wings.
Since the Albatross bird doesn't need to flap their wings as much to stay in flight and can soar most of the flight that makes it possible for the bird to stay in flight for several years.
The Albatross bird spends at least the first six years of their lives and sometimes longer staying in flight in the air.
So the Albatross can stay in the air for as long as at least 7 years before landing but maybe longer.