SA Novespace of France operates an Airbus A310 (F-WNOV) to perform 'parabolic' flights. During these flights, the aircraft simulates weightlessness for a short period of time. The cabin of the aircraft is therefore mostly empty, to give people the space to float around.
Astronauts from ESA use these flights to prepare themselves for weightlessness in space. See for an image what parabolic flight maneuvers are: https://www.researchgate.net/profile/Paolo-Lunghi-2/publication/314285521/figure/fig2/AS:469569253974026@1488965442721/Parabolic-flight-sequence.png
