Imagine driving your car, you want to slow down slightly so you lightly touch the brake...suddenly your brakes lock up hard. Totally different braking systems of course but that's the result. Kickers have been around about as long as air brakes, years ago they were also known as ''dynamiters". Various cures have been tried over the years including heavier springs on some of the internal components of the brake valves, different lubrication, and others. Nothing has totally cured the problem.
In the case you mention, the crew was doubly unlucky. When the train dumped, it pulled out a drawbar and apparently either derailed the car it came out of, or knocked it off center. But in the process it hit the angle cock and closed it. Freaky but it has happened. When the train stopped and the engineer released the brakes, the air restored. Maybe they had already had problems with the kicker that trip, but the crew didn't walk the train. They figured because the air came back up, it was only a kicker. After they went about a mile the derailed car came to a switch and the truck came totally out from under the car.
Today's rules require you to inspect the whole train after an emergency application such as this but you didn't give a date on the incident so maybe such a rule was not in effect.
Kickers are the ultimate crew alerter - seems they always happen when you're relaxed and not suspecting a thing. The standard response to a kicker is usually "Oh sh**!" in unison from all those in the cab.
