Originally Posted by
FM_A320
Dear colleagues,
I’ve just ended my Line training on A320/A321, I’d like to ask your opinion about some thoughts about energy management. In my airline we are encouraged to use OP Des and V/S for descent planning, in order to be able to compute ourself.
My question are:
/ how many miles do you add in order to decelerate? Normally I use 3xAltitude (even if some colleagues suggest 3xdistance as this gives a shallowe profile) plus 5 miles from 250. I see this rule works very good and is even conservative if I can descend all the way down at 250, level off and decel, configure.
if I have some altitude constraints where I have to decel quite early to 210, I see I have some problems as then the gradient is very shallow and soon I go above profile…
/ If I have an intermediate altitude constraint say 20nm at 6000 how can I know how much to decel? I see in the same scenario colleagues going straight to Sspeed and F1, others maintain 250 as they say that 20nm at 6000 has its margin and descending at 250 is better as far from GDot (best lift to drag ratio) so descent is steeper.
Thanks for your help
Hi,
First off all congratulations for having successfully completed your line training! A little less congratulations for your trainers that have left you with those unanswered questions
Let's look at a basic but effective descent management tool.
The good old Altitude x 3 to start with.
Then adjust the wind -> +/- 10% tail/head winds
Then adjust the speed + 1 NM for every 10 kt above 200 kt which is usually somewhere around Gdot.
Finally the weight adjustment. On the narrow body Airbus I don't bother too much; if I am very light I will probably need to reduce the RoD at some stage and if I am close to Max Landing Weight I might need to use some speed brakes.
So You need to start your descent from FL350 down to your platform of, let's say, 3000 ft.
32 x 3 = 96 NM
20 kt tailwind = +2 NM
Deceleration = 7 NM (descending at 270 kt)
Start descent in OP DES around 105 NM.
From there keep calculating and adjust, every 5000 feet or so. If you do have STAR constraints to meet in the middle you will need to set targets for the different constraints.
Generally speaking this sort of technique of descending in OP DES/VS works well to optimize fuel consumption when there are not too many constraints to be considered.
It is a "homemade" version of the Descent Profile Optimization by Airbus and can lead to some savings if applied correctly.