Why Does The 777 Overspeed at 330Knots?

[ivo]

This is becuase the air up at 35000ft is thinner than the one down at 5000ft. Less air is flowing through the pilot tube, so you don't get a
reading of your ground speed. You get a reading of you airspeed. Even though you gauges might only show 290 knots, you're actually
going much faster at 30000ft.

TAS=True AirSpeed, the speed at which you move through the air.
IAS=Indicated Airspeed, the speed that you gauges show you.
GS=Ground Speed, the speed at which your plane moves over the ground.