Pulse1 - sounds like the episode recounted by one of the early post WW2 captains flying York freighters out of Lebanon. Fully loaded he entered the base of an active Cb at 6000' and hit up-draughting of such violence that, even with gear and flaps down and engines at idle, they still went up and were eventually spat out of the side at (IIRC) 26000'!!!
Stay clear of the 'thunder-bumpers'!!