Airbus Managed Descent
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Airbus Managed Descent
Hello,
Any Airbus pilots that could please give me a lesson regarding "Managed Descent" on the scarebus please
Very much appreciated
Any Airbus pilots that could please give me a lesson regarding "Managed Descent" on the scarebus please
Very much appreciated
Only half a speed-brake
Well, it is called VNAV on Boeings for start. It works pretty much the same way, especially that it is also of no use If you are NOT given the choice of T/D and track miles below FL100. Perhaps you want to be more specific? Oh, most importantly, it will also teach you itself.
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If you start it down before it's calculated top of descent it will descend at 500fpm until it reaches its calculated descent profile. Once it reaches it's profile it will go to idle thrust and go hell for leather downwards to reach its target altitude, reaching disturbing nose down pitch attitudes and uncomfortable rates of descent which you will have to maintain in order to met the constraints. It will also leave you in the lurch if you are given a heading to fly which takes you out of NAV mode as the vertical mode will revert to V/S rather than DES and will not adjust that V/S itself. My best advice is leave managed descent well alone unless you are the only aircraft in the sky because it doesn't do the job very well.
Nonsense.
Managed descent really does do a splendid job and is calculated to try and achieve a glide descent (i.e thrust idle) from top of descent to touchdown. Speed limitations (i.e. 250 kts below FL100) and level/altitude constraints are also factored into the calculation.
If the MANAGED descent is started prior to the computed top of descent, the aircraft will descend at 1000 fpm until reaching the correct vertical profile.
It does not reach scary speeds or ridiculous nose down attitudes. Regarding speed; it will stay within certain limits of the required speed in order to stay on the vertical profile. For example, if the required speed is 250 kts, on a managed descent, if high, the aircraft will only pitch down to achieve 255 kts to try and increase the rod. Conversely if below profile, it will reduce speed to 240 kts.
The managed descent is a very effective and very efficient system (and understands how it works!). If of course the idiot trying to use it does so properly. However, if the said idiot is incapable or indeed an individual does not wish to fly a managed descent there are primarily two different methods. An open descent (i.e. thrust idle and the aircraft will pitch down to achieve the required speed completely disregarding the vertical profile) or vertical speed can be used (ie. the required fpm during the descent is set on the FCU and the aircraft will fly that rod).
Hope this clears up your queries.
LOC
Managed descent really does do a splendid job and is calculated to try and achieve a glide descent (i.e thrust idle) from top of descent to touchdown. Speed limitations (i.e. 250 kts below FL100) and level/altitude constraints are also factored into the calculation.
If the MANAGED descent is started prior to the computed top of descent, the aircraft will descend at 1000 fpm until reaching the correct vertical profile.
It does not reach scary speeds or ridiculous nose down attitudes. Regarding speed; it will stay within certain limits of the required speed in order to stay on the vertical profile. For example, if the required speed is 250 kts, on a managed descent, if high, the aircraft will only pitch down to achieve 255 kts to try and increase the rod. Conversely if below profile, it will reduce speed to 240 kts.
The managed descent is a very effective and very efficient system (and understands how it works!). If of course the idiot trying to use it does so properly. However, if the said idiot is incapable or indeed an individual does not wish to fly a managed descent there are primarily two different methods. An open descent (i.e. thrust idle and the aircraft will pitch down to achieve the required speed completely disregarding the vertical profile) or vertical speed can be used (ie. the required fpm during the descent is set on the FCU and the aircraft will fly that rod).
Hope this clears up your queries.
LOC
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it will stay within certain limits of the required speed in order to stay on the vertical profile.
I reckon there are two types of Airbus pilot: those who've seen the autopilot/FMCG do unpredictable things and those who are about to! Managed descent works OK based on conservative descent speeds with benign weather conditions. If you're flying around at a high cost index with significantly varying winds in the descent and turbulence it has the capability to make your day really exciting.
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Managed descent works extremely well, and very much as Localiser wrote. It does however need the winds to accurately inserted in order for it achieve a steady path.
Imagine planning your own descent without planning for the wind, and simply having to react to a rapidly changing situation - you would do the same thing to recover the descent profile.
Imagine planning your own descent without planning for the wind, and simply having to react to a rapidly changing situation - you would do the same thing to recover the descent profile.
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From my personal experience flying single isle Airbuses I can say that, if you put in the descend winds you are getting most of the time a nice managed descend. If you don't put them in it might end up in very interesting profile.
Going on radar vector I used always open descend or V/S depending on the situation.
Going on radar vector I used always open descend or V/S depending on the situation.
So back to my original point... If the individual understands how to use it correctly, it works more than adequately.
Nb. No FCOM quotes were used or hurt during the production of my posts
Nb. No FCOM quotes were used or hurt during the production of my posts
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Thanks all for the replies, i created the topic purely to understand this method a bit better and to gain knowledge between the flow of posts from you pro's, i fly something much smaller, but it's french 
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Airway,
My two cents; the Managed descent PROFILE is directly related to the cost index your company uses(1-100), my company uses 35 and the airplane does a great job(320/321), unless you manage the descent after passing the TD top of descent the aircraft is very smooth, I regularly fly long STARS with several crossing restrictions and it does fine. Carnage may have been using a high cost index or in poor wx conditions, not sure.
Dream Land
My two cents; the Managed descent PROFILE is directly related to the cost index your company uses(1-100), my company uses 35 and the airplane does a great job(320/321), unless you manage the descent after passing the TD top of descent the aircraft is very smooth, I regularly fly long STARS with several crossing restrictions and it does fine. Carnage may have been using a high cost index or in poor wx conditions, not sure.
Dream Land
Only half a speed-brake
awy:
Oh, in that case, we still owe you the answer.
On a jet, the most fuel efficient way to descend is of course to stay in the optimal cruising altitude as long as possible, then cut the thrust and glide with a certain glide speed to the destination deceleratate for the approach, and, ideally you only advance throttles as far as the outermarker to spool up for go-around.
Simply put, the speed (i.e. steepness of your glide/dive
) calculation is based on economic fuel to flight time ratio (the cost index). So all you have to do is make a good decison about the top of descent point observing all the speed and altitude constraints ahead. Which is, obiously the tricky part.
For this regime the autopilot interface has a mode selector named Level Change (B) or Open Descent (A).
Should you find yourself short of the field, either you slow down (shallow your descent) - not good as you accumulate extra time on the flight, or add thrust - fuel penalty, the lower the worse.
If, on the other hand, you are coming in 'long' you can dive instead of glide, but this brings extra speed / energy you need to dissipate anyhow (search hot and high) or you can use the speedbrakes / lower the gear early which is definitely bad for your masculine ego (by many considered by far the least acceptable option of all above) . Either way, you've been uneconomical because you could have started descent earlier - saving fuel by cutting throttles sooner.
To help pilot with this task (the irony of the word) manufacturers designed a feature in their flight management/guidance computers. On "A" called Managed Descent on "B" V-Nav. One should stuff the machine with all sort of available data, e.g. constraints, altitude winds and temperature, transition altitude and QNH (1033 gains you about 550 ft which at late stages could make or break your day). Also the expected use of anti ice (some engines would spool up injecting energy to the airframe). What you get, is a glide trajectory the aircraft should follow on the precomputed profile.
As opposed to the LVL CH / OP DES method, main guidance here is the descent angle instead of speed and that is quite off the piloting basic rules, takes some time getting used to but works fairly OK at the end of the day. This should take you to FAP / FAF.
Yet, the what ifs remain. In the classical" way you fear of the altitude, in VNAV you fear of the speed. Abrupt disturbances in Open Descent fill pilots brain lobes, in Managed, passeneger barf bags (overstated on both examples, of course).
Cheers,
FD
(the un-real)
On a jet, the most fuel efficient way to descend is of course to stay in the optimal cruising altitude as long as possible, then cut the thrust and glide with a certain glide speed to the destination deceleratate for the approach, and, ideally you only advance throttles as far as the outermarker to spool up for go-around.
Simply put, the speed (i.e. steepness of your glide/dive
) calculation is based on economic fuel to flight time ratio (the cost index). So all you have to do is make a good decison about the top of descent point observing all the speed and altitude constraints ahead. Which is, obiously the tricky part. For this regime the autopilot interface has a mode selector named Level Change (B) or Open Descent (A).
Should you find yourself short of the field, either you slow down (shallow your descent) - not good as you accumulate extra time on the flight, or add thrust - fuel penalty, the lower the worse.
If, on the other hand, you are coming in 'long' you can dive instead of glide, but this brings extra speed / energy you need to dissipate anyhow (search hot and high) or you can use the speedbrakes / lower the gear early which is definitely bad for your masculine ego (by many considered by far the least acceptable option of all above) . Either way, you've been uneconomical because you could have started descent earlier - saving fuel by cutting throttles sooner.
To help pilot with this task (the irony of the word) manufacturers designed a feature in their flight management/guidance computers. On "A" called Managed Descent on "B" V-Nav. One should stuff the machine with all sort of available data, e.g. constraints, altitude winds and temperature, transition altitude and QNH (1033 gains you about 550 ft which at late stages could make or break your day). Also the expected use of anti ice (some engines would spool up injecting energy to the airframe). What you get, is a glide trajectory the aircraft should follow on the precomputed profile.
As opposed to the LVL CH / OP DES method, main guidance here is the descent angle instead of speed and that is quite off the piloting basic rules, takes some time getting used to but works fairly OK at the end of the day. This should take you to FAP / FAF.
Yet, the what ifs remain. In the classical" way you fear of the altitude, in VNAV you fear of the speed. Abrupt disturbances in Open Descent fill pilots brain lobes, in Managed, passeneger barf bags (overstated on both examples, of course).
Cheers,
FD
(the un-real)
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There's a big manual about all this, that came with my conversion
training. But I must admit, I've never read it in full detail.
The whole managed descent thing is much too conservative and sometimes even uncomfortable.
And in european airspace a descend never happens the way the
computer would like to do it. So I hardly ever use it.
It can work, if you're free to do whatever you like (no ATC restrictions) and if you set certain gates manually to make things
a bit more efficient (Descend-Profile and Speed).
Cheers, jojodel
And one more thing...
It\'s not an Airbus (which are very good and reliable planes) Problem. Also on F-100 or MD-11 it\'s the same as described in my earlier reply (the same manufacturer of the FMS?)
But now I\'m off to my local pub...
Have a good evening, jojodel
training. But I must admit, I've never read it in full detail.
The whole managed descent thing is much too conservative and sometimes even uncomfortable.
And in european airspace a descend never happens the way the
computer would like to do it. So I hardly ever use it.
It can work, if you're free to do whatever you like (no ATC restrictions) and if you set certain gates manually to make things
a bit more efficient (Descend-Profile and Speed).
Cheers, jojodel
And one more thing...
It\'s not an Airbus (which are very good and reliable planes) Problem. Also on F-100 or MD-11 it\'s the same as described in my earlier reply (the same manufacturer of the FMS?)
But now I\'m off to my local pub...
Have a good evening, jojodel
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Folks
Can I ask a question please re something I am trying to resolve, although I think you have already given me excellent material for thought to far on this thread.
Here is a specific case. 30 Nm to run and 250 kts, at 8500 above airfield level, straight in approach from 30 Nm to the ILS/RWY.
How much difficulty in achieving this approach?
Add 20 Kts up the derriere - only at the higher levels of course as it is opposite to the SIA so there is probably going to be a small shear and change somewhere on the way down. Still achievable without pilot insanity?
I would value some expert debate on this one.
Can I ask a question please re something I am trying to resolve, although I think you have already given me excellent material for thought to far on this thread.
Here is a specific case. 30 Nm to run and 250 kts, at 8500 above airfield level, straight in approach from 30 Nm to the ILS/RWY.
How much difficulty in achieving this approach?
Add 20 Kts up the derriere - only at the higher levels of course as it is opposite to the SIA so there is probably going to be a small shear and change somewhere on the way down. Still achievable without pilot insanity?
I would value some expert debate on this one.
Only half a speed-brake
I am no expert I just like to talk
. From my little time (737,320-1), no problems at all in your scenario. If you are allowed to keep 250 in continuos descent down to intermediate APCH altitude and decelerate in level flight, this would be even "unnecessary" low. For continuous descent and deceleration, I find it is just about the perfect figure. On the other hand if you have 270 kt and are asked to slow say 220 at 25 DME, there may be only little room to play with but upon slowing down, selecting the first flap setting did work just fine for me.
Cheers,
FD
(the un-real)
. From my little time (737,320-1), no problems at all in your scenario. If you are allowed to keep 250 in continuos descent down to intermediate APCH altitude and decelerate in level flight, this would be even "unnecessary" low. For continuous descent and deceleration, I find it is just about the perfect figure. On the other hand if you have 270 kt and are asked to slow say 220 at 25 DME, there may be only little room to play with but upon slowing down, selecting the first flap setting did work just fine for me.Cheers,
FD
(the un-real)
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FD
Much appreciated. Same hold for 20 Kts tailwind?
Any other Airbus or Boeing drivers who can comment? The profile seems to meet the ICAO PANS OPS requirement but the matter I am looking into claims pilot workload goes into overload on such an approach.
From what I have read on this thread it seems as though the accountants and the CI, not the pilots, are creating the overload situation if such exists?
Much appreciated. Same hold for 20 Kts tailwind?
Any other Airbus or Boeing drivers who can comment? The profile seems to meet the ICAO PANS OPS requirement but the matter I am looking into claims pilot workload goes into overload on such an approach.
From what I have read on this thread it seems as though the accountants and the CI, not the pilots, are creating the overload situation if such exists?
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As long as descent winds are inputted, the airplane compensates well for the tailwind, if winds are not in the box, the pilot will have to do some pilot stuff(if all else fails, throw out the skates), still very easy and manageable. 
D.L.
D.L.
