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james28

A330 Professional Dive on Descent

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In managed Mode Descent, is it supposed to dive so rapidly?  I'm talking from after the Descent Prep checklist, and selecting managed mode descent from cruise level, the green dot goes for a dive of the PFD and the aircraft attempts to follow it, taking it to something in excess of 3000ft/min sometimes...  It eventually catches up to something normal around 2000-1500 ft/min but really, that first dive is terrifying for the passengers, Is this how it is supposed to work???

 

If it is not supposed to do this, then is there a fix???

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Hi James,

 

The FMGS calculates the descent profile taking many variables in account such as distance to destination, air speed, weather, weight etc etc.  This is what the aircraft is trying to capture.

 

In the real world,  Airbus and Boeing pilots allow the aircraft to gradually settle onto the descent profile first using a shallow rate (e.g. 500 feet/sec) for passenger comfort.  They will then make small adjustments to the rate of descent to reach the assigned altitude in line with the calculated profile, using speed brakes as required.

 

You are right - if you engage managed descent or VNAV from cruise,  in some circumstances your passengers and flight attendants may end up on the ceiling and you will be summoned to a tea and biscuits meeting with your chief pilot! 🙂

 

I think Aerosoft are also working on the VDEV code, so it's possible that it may become more forgiving. 

 

I prefer a blend of open descent / managed descent.

 

Dave.

 

 

 

 

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16 hours ago, djspatrick said:

In the real world,  Airbus and Boeing pilots allow the aircraft to gradually settle onto the descent profile first using a shallow rate (e.g. 500 feet/sec) for passenger comfort.

 

In the Boeing (at least the 737), there is no need to set a shallow rate of descent prior to capturing the descent profile, the capture is built in to the descent profile. The Airbus is different. Prior to TOD, if you enter managed descent, it will give you a 1000ft/min descent rate until you've intercepted the profile.

 

I have seen a few cases of strange descent profiles in the AS 330, where the vertical profile jumps around excessively during descent as well. For me, it typically happens around the 10,000ft mark, whilst the aircraft is slowing from profile speed to 250 Knots.

 

The AS 330 also has an issue with excessively pitching nose low to capture the set speed in open descent mode, if you are below that speed.

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Two videos attached from my recent decent, there is a deviation of the vertical path at TOD that seems to correct itself. Then there is also a video demonstrating the excessively nose down pitch in OP DES mode.

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22 minutes ago, Sharkbait said:

Two videos attached from my recent decent, there is a deviation of the vertical path at TOD that seems to correct itself. Then there is also a video demonstrating the excessively nose down pitch in OP DES mode.

 

Yes this what happens for me too, I just did a flight and after the Descent Prep checklist I selected Open Desc first and when all was settle, I selected Managed Mode and then checked the MCDU Prog page and I was 4,500ft high on profile...  Even when I selected OP Desc in the first instance, the green desc profile dot dived way down.  Anyway, I will update to 1.0.0.6 now and see how that goes.

 

Thanks for the vids and the info.

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Same here. Happens on every flight regardless of weather and route. I can only descend in vertical or open climb modes.

 

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Thanks for the reports. We'll try to have a proper look into VNAV and OP DES logic at some point but bare in mind that it's a huge area that might take some time.

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well, the first video looks like a perfect emergency descent initiation. May be the reaction is faster than the RL counterpart. But it can really and easily reach those VS rates.

On the second one, since you started the descent well past the TOD the plane will really dive to catch the profile as long as it remains within the magenta speed brackets. they do make this dives quite sharp and "uncomfortable"

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52 minutes ago, Viperlead said:

well, the first video looks like a perfect emergency descent initiation. May be the reaction is faster than the RL counterpart. But it can really and easily reach those VS rates.

 

Yes, it can, but it shouldn't go to 7 or 8 degrees nose down to catch up to the airspeed like that, for a 2000ft descent.

 

52 minutes ago, Viperlead said:

On the second one, since you started the descent well past the TOD the plane will really dive to catch the profile as long as it remains within the magenta speed brackets. they do make this dives quite sharp and "uncomfortable"

 

That's the issue, the descent wasn't late per the ND. Have a look at the TOD arrow. Descent was initiated before reaching, by about 2.5nm, but then it's immediately 1300ft high on profile.

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