Recently on the Kerrville ramp, there was a Challenger bizjet parked and secured. A Gulfstream was under tow to parking near the Challenger. The line person put the Gulfstream in place, unhooked the tug, but neglected to chock the wheels.
[You know what’s coming, right?] The Gulfstream started rolling and ultimately an engine collided with the windscreen and cockpit of the Challenger.
