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Mark Oxley

Decent Path

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Hi Thanks for a great update but one issue which is a major one is the decent path.

 

I begin decent just before tod and the aircraft descends at -1000 ft pm then suddenly the descent path drops to 6400 ft pm.

 

The aircraft seems to be constantly chasing the purple descent marker.

 

Regards

 

Mark

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Hi Mark,

 

could you tell us some routes in which this happened to you and show us some screenshots?
What is the FMA reading in such situations?

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Hi, I'm having the same issue, I'm not at home at the moment but when I am I'll post screenshots. Whenever it happens everything is set to managed, I'm at cruise, ATC clears me to descend, I dial in the requested altitude, push the button in to go to managed descent, and it just nosedives like a rock at 6000 fpm even though I'm ~10nm from TOD.

 

I know it's not helpful with just words but I'll try to record it later when I get home.

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I've also seen the plane pitch down to -6000 fpm or higher decent rate when it's trying to race after the vnav path. This will result in overspeed. This is with managed speed and descend mode.

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Hi

 

Same here. No way to get a smooth descend. The AP does not follow the magenta dot.

 

brgs

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Yes, we have found conditions that make this hard. It's being looked into by one of our developers.

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Yes generally you want to engage descent just prior to to the T/D so the A/P doesn't get behind the airplane.

 

I too was getting up to -4400 where I just stopped it there and took over in V/S and brought it back down to 2500. Sometimes you have to be a pilot and not let the airplane get away from you.

 

The issue right now, at least evident to me is the fuselage drag coefficient in the FDE at flight idle in the upper FLs. It drops too much speed at idle in the descent so the A/P has to try to keep the target speed with pitch.

 

Most airplanes of this size should be able to remain on target speed at flight idle with a -1990 to -3000 fpm descent rate or with a little bit of speedbrake help (757 comes to mind). The airplane has lots of momentum and energy as you descent, most of which you bleed off when slowing for 10K or whenever the decel point is.

 

It drops speed currently almost as much as it should at a more level AoA. But as Mathijs said the dev team is look into it.

 

The more feedback they get the better. So they have an idea how to resolve it :) 

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After a few weeks of testing, all is good, apart from excessive decent rate in some conditions. If you are above the descent path required by the flighplan (for whatever reason e.g. missed TOD or ATC instructions), the aircraft will try to aggressively descend , irrespective of the aircraft's safe capabilities, the descent rate can be well above what would be considered acceptable in normal airline ops. This can lead in certain circumstances to being unable to meet the 250kt 10k restriction, even with full spoilers, and difficulty in safely adding flaps during the approach phase. It doesn't appear to have a "decent path unachievable" correction in the flight logic, or if it does, it doesn't work properly. This is not what I remember from the original AS Airbuses, which would pitch up if the speed was getting out of control (I think?).

Other than that, am very pleased with the new buses!

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But that is an issue that the real Busses also have. There are dozens of web pages on Descent Management and it's not a bad idea to read some of them. The speed and moment of entrty are rather critical.

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