Originally Posted by
shared reality
Well, as a long time Boeing driver previously, I was quite astonished wrt the incredibly inefficient descent profile on the A320. In my airline we are very fuel conscious and flt ops go to great lengths as to push for efficient, green ops when / where possible.
We have a mix of ceo and neo. Our neo´s are all equipped with DPO (descent profile optimisation), which make the managed descent profile a little less poor.
In my book, any professional airline pilot should strive for an IDLE descent from TOD until just about at the approach stabilisation gate (1000ft AAE).
I know that this is not always possible as ATC /airspace restrictions etc play a part, but when able that is what we do. It is smooth, saves both money and the environment, and is part of the fun of always trying to make the "perfect" flight.
So, we have something on the non-DPO ceo we call the "10% rule" : This means we go beyond the TOD and start descend in OP DES to stay 10% abv the airbus profile. Ex, you cruise at FL350 and dest is at sea level. This means you pull for OP DES app. when you are 2700 ft high (it takes quite long for the bus to go from level flt to get the nose pointing down..). This will put you app 3500 ft (10%) abv the profile initially.
Since you are at an efficient idle, your descent profile will slowly close towards the airbus profile, and you continuously x-check as you descend (passing fl 300 you will be app 3000 "high", at fl 200 2000ft "high" etc, you get the point.
This works great, again, on a non DPO aircraft.
As for the neo, with DPO, I simply go past the TOD with app. 300-400ft then pull for OP DES.
If winds are a bit off etc, you simply have to pull for selected speed and adjust to play with the energy of the aircraft to stay on the idle profile.
Someone might now think, what about constraints? How do you ascertain not busting any alt constraints on the way down if you are not in DES mode??
Simples, again using the "10%" rule: cruise FL350, cross XXX VOR at or below FL150, diff between FL350 and FL 150 is 20000 ft. You simply start down with being 2000ft "high" and monitor on the way down. If that is a problem for any half decent pilot, then our industry is in worse shape than I thought.
Again, as professional aviators, we should take pride in operating as safe, and as EFFICIENT as possible, and a generic diff between OP DES vs DES is app 30% more fuel burn in DES. That is in my opinion, sloppy.
However, if I am performing an RNP AR approach with multiple close-to -each-other alt constraints during the approach, then I set the temp corrected Final Descent Point altitude on the FCU, and press DES, as it will reduce workload quite a bit as the DES will pass each constraint correctly without me having to sit and change FCU alt numerous times on the approach. //TRI/TRE at a European legacy.
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