Airbus don't expand on it.. it is the distance required to go down, slow down, configure the aircraft and land at destination. In a straight line, not taking account of the F-PLAN route. Not displayed in NAV, only in HDG or TRK lateral modes.
How to use it? Imagine a straight line to the runway, and a/c on the centreline.. if the energy circle is beyond the runway, you have too much energy and will have to take appropriate action. If the circle lies between you and the runway - no problem.
Last edited by TyroPicard; 9th December 2009 at 14:29.