Tne West Collection say it best:
Schabel's celebrated series of "Passenger" photographs were taken during that space in time that occurs when people have been seated in their seats, but the plane has not yet taken off. His muted, black and white images capture people completely unaware that they are being photographed. Schabel himself was inspired by his own fascination with airplane journeys and the whole amalgam of experiences that can be found within a flight.
via It's Nice That.