Originally Posted by
VegassBus
It's the best way to get down & slow down at the same time, not sure what you are arguing
If you are at at 5,000 ft and Doing 250 and told to "slow to 200 and descent and maintain 2000, turn HDG blah blah. In Open descent it won't really start coming down until the speed is back. Why not dial in -1,000ft and spin the airspeed to 200? It will immediately go to idle and almost immediately start the descent as opposed to the lethargic open descent and roll speed back method.
Your technique may initially get the aircraft started down quicker (a function of how fast the auto thrust reduces engine power in the different a/p mode).
But with your technique, as the airspeed approaches 200, the auto thrust will add engine power to maintain both the 200 knots and the 1000 fpm descent (your FMA will change from 'idle' to 'speed' indicating that engine power has been added).
This addition of engine power will ultimately delay the amount of time to achieve the desired altitude loss. The use of 'open descent' will prevent the addition of any engine power until needed for level off (your FMA will remain in 'idle' during the descent).
With your V/S technique, how much engine power is added will be a function of what v/s is selected. Just realize that ANY addition of engine power will delay your descent.