Being a quad, there is less concern with a 747 jumping the chocks during a high power run than with the big twins like the 767 and 777. Rather, the primary concern is with the side forces on the nose wheels.
Many years ago, I was in the flight deck on a 767 during high power trim runs when the nose gear moved sideways
- I was mildly amazed at how quickly the engine run guy had the throttles at idle
.
There had been a hydraulic fluid spill near the nose and the tires slipped on the hydraulic fluid. The ground crew reported the nose had moved about six inches - those of us in the flight deck thought it had been more like six feet
.