Is air weightless?

NASA's KC-135 Reduced Gravity Aircraft is based at Lyndon B. Johnson Space Center and affectionately called the "vomit comet". It is an airplane that NASA flies in 6 mile long parabolic arcs, first climbing in altitude, then falling, in such a way that the flight path and speed correspond to that of an object without propulsion and not experiencing air friction. This is realized by propulsion and steering such that air friction is compensated and nothing else. The result is that people inside are not pushed towards the bottom or any other side of the plane, i.e. they are temporarily weightless, each time for a period of 25 seconds. Typically one flight lasts about two hours, in which 40 parabolas are flown.