Means jacking off on an airplane in flight. Usually done in toilet cubicle or underneath an airplane blanket. An elaboration on Mile High Club that has long meant sexual congress on an airplane.
"You mean, join the Solo Aviator Division? That's SAD! (chuckles). As a flight attendant, I see all sorts of things, like splooge in the unisex toilets the last visitor didn't even clean up. And you wouldn't believe what goes on under those airline blankets."
"Yuck! Now I know why they're so skanky. Thanks for the warning."