Originally Posted by
1201alarm
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.
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.