Originally Posted by
tdracer
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
.
You are correct that asymmetric thrust is a high concern on the 777. In fact, it has something called Thrust Control Malfunction Protection. The EEC provides protection against an uncontrolled high thrust malfunction during ground operation and automatically shuts down the affected engine when the thrust lever is at idle, and the engine is above idle speed and not decelerating normally.