Based on Season 1, Episode 4 "Phantom Traveller"

Despite the fact the demon had been exorcised and the flight was now diverted from its route to hell, Dean was still uncomfortable with the ordinary odds of a plane crash. He had therefore once again worked himself up into a frenzy, now an hour into the flight.

His knee bobbed up and down while his eyes searched frantically down the aisles for an escape – possibly a door into another dimension. Anything really. His head snapped back up when he felt Sam's hand on his knee.

"Calm down dude, the worst is over"

"We are in the fricking air Sam – and I don't think gravity owes me any favours"

Sam sighed momentarily, before breaking into a grin. "I do"

"What are you on about?" Dean gave him a puzzled look.

"You got on this plane even though you were petrified and helped me defeat a fiend from hell. I recon I'm in your debt"

"Yeah well, you can clean the Impala when we land"

"Actually, I had something else in mind" Sam breathed into Dean's ear, and swiftly stroked his hand up the inside of Dean's thigh and to his crotch.

"What the...!?"

"Shhh, I'm helping you relax"

And as loathe as Dean was to admit it, what happened next really took his mind off flying. Dying. Well – anything really.