A320/A321 energy management and configuration

[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

[321XLR]

General Rules of Thumb

The short answer to this is all Arrivals should be via Managed DES and with the PROG page displayed. As soon as you get high above your profile, use the speed brakes. If you have a tailwind, especially on the 321, be especially attentive to the descent. V/S means Very Seldom. Some guys love it and use it like a master, but your protections are gone in V/S. Use V/S out of 12,000, speed 300, down to 8000, and you will soon be flying 300 knots below 10,000 feet, thus busting the 250 below 10,000 rule.

"Open" XXXX (climb/descent) should primarily be used with ATC says "....and maintain" with the clearance. Intermediate descents, say 350 down to 310, due to turbulence at 350, is a DES not Open Descent.

I don't get too worked up over the math I watch the intercept path symbol and descent arrows, and level off point, to manage stuff. I don't have my head in the sand, blindfully ignorant either, but I am just not doing math equations for my descents. I might use "math" for a sanity check nothing more. I am not calculating decel points or things like that.

Also, it is easier to "get down first" then slow down once you level off, versus try to slow down, AND get down. The Airbus really does not slow down and get down well at the same time.

If in the airport environment aka "talking to Approach" and speed 210, go to Flaps 1. Downwind is typically speed 210. Base turn, speed 170-180, Flaps 2.

Watch the VLS with spoilers out, some instructors will tell you "it doesn't matter" if you airspeed enters VLS, others will break your kneecaps if VLS touches your present speed. Speed 210 with Flaps 1 largely mitigates that.

Again, general rules of thumb. Adjust for the operational situation at hand.

[sonicbum]

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 :ugh:

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.

[tubby linton]

321XLR I don’t know what protections you are talking about. You are fully protected in V/S mode. Perhaps you mean mode reversions, they are described in DSC 22_30-40-110

[snl13]

321XLR I don’t know what protections you are talking about. You are fully protected in V/S mode. Perhaps you mean mode reversions, they are described in DSC 22_30-40-110
I think he meant that when you go on V/S plane will keep ROD and speed could keep increasing during descent if you ask for too much v/s, and go faster than atc/company restrictions. Whereas in OP DES ROD will reduce to try to maintain the desired speed.

[FM_A320]

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 :ugh:

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.

Thank you very much!
Unfortunately during training I see some captains are not really able to transmit those things, on energy management sometimes they just rely on experience and feeling in order to judge descent and configuration, which is obviously perfect and normal after many hours, but for a fresh new pilot cadet level some rules of thumb and guidance are still required, as experienced needs to be built…
Thank you for your help, I’ll try. Sometimes I get a common restriction with 9000/29 nm before joining an arc dme and descending on the arc. I reduce to speed 210 and then maintain this speed in order to avoid overshooting. When descending gradually I see losing miles (especially with 10kts tailwind), I try to solve going F1 speed 210 and sbrake but it’s not really efficient and couple of times had to use the gear… Not nice that feeling of rush thinking “will I make it or not” :) Probably also the plane makes the difference… some of them look very reluctant to descend steep

Thanks again for the help.

[tubby linton]

I think he meant that when you go on V/S plane will keep ROD and speed could keep increasing during descent if you ask for too much v/s, and go faster than atc/company restrictions. Whereas in OP DES ROD will reduce to try to maintain the desired speed. That used to be called airmanship and managing the platform in my day. The FCTM stated 250kt/ 9000 feet above the airfield at 30nm. When I first started flying Airbus every approach was meant to be a decelerated approach and taking flap as soon as you got to target speed as long as you were on the profile. The FCTM seems to have taken out some of this info but it states that the typical descent is based upon n FPA of 2.5degrees.

[easymxp]

That used to be called airmanship and managing the platform in my day. The FCTM stated 250kt/ 9000 feet above the airfield at 30nm. When I first started flying Airbus every approach was meant to be a decelerated approach and taking flap as soon as you got to target speed as long as you were on the profile. The FCTM seems to have taken out some of this info but it states that the typical descent is based upon n FPA of 2.5degrees.

I agree a common figure, also in the FCTM and many Airbus FOBN is 250/9000/30. Tbh a part from descent with light weight and a normal amount of headwind I feel on the high side at this distance and height. 9000 at 33nm is generally a better starting point, but I play maybe in the conservative side.

[sonicbum]

Thank you very much!
Unfortunately during training I see some captains are not really able to transmit those things, on energy management sometimes they just rely on experience and feeling in order to judge descent and configuration, which is obviously perfect and normal after many hours, but for a fresh new pilot cadet level some rules of thumb and guidance are still required, as experienced needs to be built…
Thank you for your help, I’ll try. Sometimes I get a common restriction with 9000/29 nm before joining an arc dme and descending on the arc. I reduce to speed 210 and then maintain this speed in order to avoid overshooting. When descending gradually I see losing miles (especially with 10kts tailwind), I try to solve going F1 speed 210 and sbrake but it’s not really efficient and couple of times had to use the gear… Not nice that feeling of rush thinking “will I make it or not” :) Probably also the plane makes the difference… some of them look very reluctant to descend steep

Thanks again for the help.

No worries.

Next time take your 9000 ft as your aiming point and calculate from there. You should end up there with Gdot ready for your arc.

To crosscheck how you are doing during descent also use the "official" Airbus formula:
Required Dist to descend = Diff. in FL / FPA
I.e. I am passing FL250 descending FL90 or 9000 ft like in your case so that's a Delta of 160 divided by what the bird shows, let's say 4° probably -> 40NM needed bare minimum distance. That's where all the psychometrics pain in the a°rs math tests come in handy :E

You can monitor you current FPA in Descent by occasionally going bird ON and see how you are doing.

As a general rule try to correct your descent profile while still far from the target as you will have many more tools, such as increasing your IAS and using speedbrakes. This combination can double your descent gradient when you're still far out and can afford higher rates of descent and speeds.
Below FL100 you will mostly be on a 3° descent on idle thrust, that you can increase by adding speed brakes and bring it up to even 7° by going full manual speed brakes at 250 kt but there are some threats involved in doing that (high rate of descent below FL100, manual flying with tunnel vision). So I would recommend to keep your AP on and accept the half speed brake of the A320.

During your next flight go Bird ON from time to time during descent and see how the aircraft behaves at different levels, how air density variations and wind changes affect your descent gradient. That should help :ok:

[mustafagander]

First caveat-I'm not an Airbus pilot. I have been around a very long time though and as I see it your best way to learn is to glean all the worthwhile info from threads like this.

Plan EVERY descent, even as PM fly it in your mind, so that you will build an experience base to work from.

When you are PF fix any errors you see as soon as you see them. Say you're high and fast around 10,000 ft, fix it now don't hope it gets better. You may be wrong with your fix and it would have fixed itself but you demonstrate to any watchers that you have a plan and are aware of variations. This is the stuff that makes aviation interesting and worth doing, the fact that the air is unpredictable.

Accept that even after 45 years you will NOT know it all and keep learning and enjoying the way that things almost invariably change. That's what I did and enjoyed my career immensely.

Good luck!!

[PapaEchoIndia]

Generally altitude x 3 times with 1 nm per 10 kt reduce in the speed works well in my experience but what I did (and actually still do is); I enter the runway or the faf to the PROG page and make all the calculations and planning aloud, like "ok we have xx nm to faf, we are at xx feet, we are high/low, I will do this/that", then as written above everyone in the cockpit knows you are aware of the situation and have a plan, and secondly everyone will share their experiences based on the situation.

[CVividasku]

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.

Hi,
The more correct formula is "altitude/slope = distance". Altitude x3 puts you on a 3.33° slope (approx) so is indeed steeper.
A good rule of thumb is to add 5 miles for 320kt to 250, and another 5 miles for 250kt to under VFE2.

If you're about 500-700ft above profile you should be more than okay for a decelerated approach (at least on my FMS standard which wants to do an early stabilized..)

If you're (very) high, it's usually best to slow speed first, get flaps 2, full spoilers (sometimes gear down even) and then dive. This will give you almost 10 degrees..

To avoid unstabilzed approaches, I put the runway in prog page and don't turn to base then final unless my altitude is lower than distance x 3 + 1000ft (to account for the turn)

You can also compute your own FPA. Compute your nautical miles per minute first : 120kt is 2 nm/min, 180 is 3 and so on. Just use the nearest figure, closest to your ground speed. Then, there is 100fpm for each degree and each nm/min. For example at 240kt, if you want to go down by one degree, you need 400fpm.

[FM_A320]

Hello everyone,

Thanks to all your advices my descent management has significantly improved. With 3*Altitude + 1nm each 10kts to lose down to 200 (+\- wind adjustment) descent goes really fine. Just one question. Sometimes ATC asks me 210 quite early due to traffic sequencing, especially at heavy weights this can give some troubles as gradient is shallower and S/brakes are very limited due to VLS (unless I use Flaps). When you expect 210 very early due you still use 3xAlt to monitor your descent, and if you start drifting high you go F1 + Sbrakes or you modify your computation to allow for this?

[Fursty Ferret]

OP DES is faster than DES even if “THR IDLE” is shown on both.

[Mark.S]

This information is quite valuable; thank you for sharing.

[321XLR]

keep in mind OPEN DESCENT up at cruise altitudes is basically a rock falling out of the sky and may trigger some TCAS alerts due to "excessive descent rate" and closure rate calculations with out traffic

I personally dont really use it unless below 18,000

[Amadis of Gaul]

What I find interesting about this question is that it gets asked all the time, and every time it's like someone is discovering something new. Personally, I'm not particularly smart, so I just use straight 3:1 rule. Has worked peachy in every type I've flown. Mind you, I am a big-time overthinker by nature, but not in this case.

[hans brinker]

OP DES is faster than DES even if “THR IDLE” is shown on both.

Have you compared fuel flow for both when THR IDLE is displayed? If the FF is the same, the descent rate has to be the same for the same speed.

[vilas]

Have you compared fuel flow for both when THR IDLE is displayed? If the FF is the same, the descent rate has to be the same for the same speed.
I don't know whether it's true now because lot of changes take place. Previously managed descent thrust idle fuel flow was at anti ice on fuel flow to keep predictions accurate should anti ice be required. OP DES was normal idle. That's why the difference.

[I-WEBA]

No worries.

Next time take your 9000 ft as your aiming point and calculate from there. You should end up there with Gdot ready for your arc.

To crosscheck how you are doing during descent also use the "official" Airbus formula:
Required Dist to descend = Diff. in FL / FPA
I.e. I am passing FL250 descending FL90 or 9000 ft like in your case so that's a Delta of 160 divided by what the bird shows, let's say 4° probably -> 40NM needed bare minimum distance. That's where all the psychometrics pain in the a°rs math tests come in handy :E

You can monitor you current FPA in Descent by occasionally going bird ON and see how you are doing.

As a general rule try to correct your descent profile while still far from the target as you will have many more tools, such as increasing your IAS and using speedbrakes. This combination can double your descent gradient when you're still far out and can afford higher rates of descent and speeds.
Below FL100 you will mostly be on a 3° descent on idle thrust, that you can increase by adding speed brakes and bring it up to even 7° by going full manual speed brakes at 250 kt but there are some threats involved in doing that (high rate of descent below FL100, manual flying with tunnel vision). So I would recommend to keep your AP on and accept the half speed brake of the A320.

During your next flight go Bird ON from time to time during descent and see how the aircraft behaves at different levels, how air density variations and wind changes affect your descent gradient. That should help :ok:

very interesting. More or less what the DPO does. But do you think on most A320 Ceo at 210 (or very close to GDot) you will be able to descend on a 3°? So 210/6000/19, 210/5000/16? I see most of the times it’s slightly shallower than 3° and deceleration takes longer….

[Cough]

321XLR - I think the differing answers come because folk are based in different continents. Most US airfields have so many altitude constraints on arrivals/departures that DES/CLB would indeed be the primary way to go (especially the descend via ATC instruction which fits this mode well). Europe has comparatively few constraints and actually some ATC units actually require a fixed descent rate (specified at the time and not charted). Ref climb/descent rates using Open Climb/Des - Our operator asks us to limit V/S approaching a cleared altitude when around other aircraft, so if in DES we would be reverting to V/S anyhow.. So yes, your answer is good for the US, but actually there are many ways of achieving the goal...

[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.

I

[I-WEBA]

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.

I

Very very interesting and makes sense. In this way you can still use managed des (or better it’s guidance while going down in OP DES) and avoid too many calculations (like 3xrule) etc.
Many times I get very annoyed with managed des descending with some thrust while being very very low.
quick question: many approaches in Europe have some “snake arrivals” that 99% are cut with a significant shortcut. Most pilots stay a bit low to be ready to accept the shortcut. Do you have any technique like this 10% rule or something else?

[321XLR]

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.

I

You are descending out of FL350 in Open D? Any TCAS alerts etc due to descent rate? How about engine noise or lack of noise and startled passengers (maybe that is a old wives tale).

Thank you

[CVividasku]

It does not cause any problem of this nature at all.
Except if you combine open descent with increasing speed from cruise to 340kt. Then maybe the cabin crew will complain about a 5° down pitch.

[TheEdge]

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.

I
I didnt know it was called "10%" rule, but this is what i do more or less whenever possible by ATC/STAR constraints or practicability.

[Uplinker]

Can anyone give the difference in fuel used between a typical descent from cruise to landing, in managed DES and open DES for, say A320 ?

As actually measured not theoretically.

[FM_A320]

Hello,

Thanks to all advices, especially sonicbum one my descent has significantly improved. Our aircrafts (mostly) don’t have DPO thus using height*3 + 1nm each 10knts down to 200 really optimizes descent.
In your opinion in busy airspace where I expect ATC will ask me to decelerate many times while descending (ie speed 220 then speed 210 then 180) do I need to stay lower and account extra margins or not? As for many subjects many captains give different feedbacks (and prompts): some of them say that even if I will get speed deceleration by ATC while descending 5nm from 250 to decelerate is perfect, others that 5nm is fine only if I can keep 250 until close to level off, decel and configure. If I expect deceleration while descending should be lower and account maybe 10nm from 250 to decel…