VNAV should still provide a reasonably accurate descent profile up to 20 nms to the left or right of the magenta line. This is based on the fact that at distances greater than 20 nms, the next waypoint will not be recognised as one passes abeam the position. In this case, the data will most definitely be invalid, including fuel, dist and time remaining.
Last edited by 777boeings; 27th Dec 2012 at 06:13.