A320 Managed descent with DPO and CDO
 

Hello everyone,

What’s your impressions on managed descent with dpo and cdo and latched profile?
TBH what drives me crazy is that it almost always needs speed brakes to decelerate to manoeuvring speeds. When at 5000 you are at 18nm and 250 it’s almost sure it will need speedbrakes sooner or later…

I’m A330, but that sounds very similar to what happens with us. In my experience, if you let DPO do its thing, every descent will have the thrust coming up at one point and speed brake being used at another. That defeats the purpose of minimising fuel burn. I believe it’s because the forecast winds loaded into the FM are different to the actual winds. What I do, is if I see that thrust or drag is needed to maintain speed on the latched path, is pull Open Descent. i.e. the aircraft is now pitching for speed (not path) and thrust remains at idle. Usually, the above and below path errors will average out and once below the stronger upper winds (and before any STAR altitude restrictions) I’ll update the FM calculated path (re-enter Vapp) and reengage managed DES. I’m usually back to being very near the path and speed brake/thrust requirements thereafter are minimal.

I have to agree with both your observations on this. My belief is that it is more to do with winds entered on the descent profile not matching with the actual encountered winds during descent. Hence, the calculations at time can be slightly off at times. Have you guys tried to back track the STAR and add pseudo constraints onto the profile (while ensuring those contracts are complaint with the published constraints) ? I have noticed when this is done a better descent profile is flown by the FMGC. However, I truly believe the DPO update is better than its predecessor.

I never understood why Airbus is not improving their calculated managed descent profile. They do all kind of things for sustainability like green procedures etc, but the FMS still calculates a speed of around 145kt when intercepting the 3° ILS-GP instead of calculating with 185kt, which is the usual speed on A320fam to go onto the glide.

This difference in projected speed by the FMS and in reality flown speed makes for a managed descent profile that is roughly 1500 ft too low. So you can't really use managed descent with the in principal cool idea that you let the machine sort out wind variations by flying within a speed bracket instead of a speed bug.

What do your companies use for IDLE/PERF Factors? My understanding is that the IDLE Factor has a large impact on the sensitivity of Managed Descent to actual winds. My company uses a 1.0 IDLE Factor, which seems to allow plenty of margin for unplanned winds in the descent.

Hi, I agree with you regarding DPO (possibly with also CDA) does definitely a better job than the previous one. Some colleagues that flew 737-300 say that this is what the 737-300 did 20yrs ago. I don’t know as never flew boeing.

yeah, I see modifying a bit the constraints helps, as gives a better profile.
In some airports also inserting (or modifying as we get auto uplink) the winds at around 5000 gives better profile. For instance in Milan many times I see tailwind on approach is far more than forecasted winds, thus adding an extra 10knts TW instead of say a 10knts xwind gives an idle and good profile…

I will pay close attention to this on my next duty, but I've had occasions where I had to insert a lower speed constraint at the FDP on some approaches with low interception altitude because the FM wanted to intercept the glideslope at 190 kts or thereabouts. A321neo in my case.

My experience on the NEOs with DPO so far has not been that bad. My operator regularly updates IDLE/PERF factors and I made it a habit from my 737 days to insert descent winds. Several times I managed to do a descent down to platform altitude, slow down to S speed and intercept the glide without any thrust being added. Just activate approach phase before the actual pseudo waypoint to avoid a momentary thrust increase at ALT* engagement. I'll agree it is not really a CDA per se and it is not what they want in the London TMA.

I think that used to be true with the old style descent planning in the FMC. With DPO/CDO it is not anymore. Easy to see if it puts the flap 1 and 2 pseudo waypoints after glide slope intercept, which can and does happen. Having updated and recent descent winds helps with that, otherwise there is a chance that one might actually be higher than planned, not lower. Resulting either in an intercept from above or speedbrake usage.

Is that such a terrible thing? Your company paid a lot of money for those speedbrakes, it would be a shame if you never used them.

People often forget about the use of anti-ice, almost always required in Northern Europe at some point in the descent. I'd prefer the DPO to be the same as Boeing, where you can enter a block of altitudes on the PERF DES page, for where ant-ice is expected to be used.

Nothing terrible, but it’s a waste of energy. If you use it means at a certain point you lost some fuel by staying higher. So yes, if the approach is what is planned without any EAI or different winds not being able to do a proper profile is quite bad

How tragic!

​​​​​​​Kindergarten must have finished for the year.