[OAC_Sparky]

Believe it or not, planes leave a "wake" of turbulent air that lasts up to two minutes after the plane goes by. When I have to land at Hamilton International I have to be mindful of the Westjets and such; what their lift-off/touch down point is (that's the spot where the wake is most concentrated) so that I don't run into it with my smaller plane. It's invisible, and it'll flip your plane no problem.

http://en.wikipedia.org/wiki/Wake_turbulence