Aside from aeroplanes, humans should not the feeling of flying, correct?
Wrong.
When Arthur makes the effort to show him how he feels – like leaving daisies with his notes if he had to go to work earlier than normal, calling him in his lunch break or kissing his cheek in public before hiding his face in Francis' chest. His ears will flush when he does that, and if he is with Francis, he won't cover them like he would with anyone else.
He doesn't say it, but he knows how to tell Francis that he is the one he will let see this, he is the one he will show his true self to.
Then, Francis feels like he has grown wings and could soar past the grimy buildings of this city, could take Arthur with him and hold him close forever. Then, he feels like he already has done and can do it again, could do it a thousand eternities over. Instead, he will just put an arm around Arthur and delight in the way that the smaller man's shoulders relax when he lays a hand on them.
And Arthur will never admit it, but he feels as though he is flying.