JW411
There are a number of stands at my local (UK) airport that slope towards the terminal building. One in particular is such a dramatic slope that local procedures have been developed to ensure chocks are in immediately the beacon goes off.
Doesn't always save the day though, just before pushback, tug attached, the chocs were kicked out by the ground staff and the a/c rolled forward catching the door on the airbridge. The brakes had failed on the tug!! As the man says, Sh1t happens.
In twenty odd years airside I've witnessed three a/c roll when no chocks were in. One was my own stupid fault and we got away with it.
Another, a DC10 rolled 40ft (away from stand forunately) when the crew assumed chocs were in and released the brakes. Again, fortunately no one was hurt and as the brakes were released so soon no equipment had time to get anywhere near.