A380 Descent calculation
Thread Starter
Joined: Jul 2013
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From: Bangkok
A380 Descent calculation
I'm converting to A380 and looking for a rule of thumb for the required distance in DES planning. Has anyone got any ideas?
Currently I use my A340 formulas which are ...
(height X 3) + 20 kts when DES speed is 300 kts
(height X 3) + 10 kts when DES speed is 250 kts
(height X 3) + 5 kts when speed is at green dot
I think it's not quite work as my DES profile always ends up too high (LDG weight approx 370 T) and cant capture G/S without speedbrake
Currently I use my A340 formulas which are ...
(height X 3) + 20 kts when DES speed is 300 kts
(height X 3) + 10 kts when DES speed is 250 kts
(height X 3) + 5 kts when speed is at green dot
I think it's not quite work as my DES profile always ends up too high (LDG weight approx 370 T) and cant capture G/S without speedbrake
Joined: Mar 2002
Aviation Qualifications: ATPL
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From: Seat 1A
I don't fly the Dugong but...
I assume by "+ 20 kts" you mean miles? If so, assuming the A380 flies like most other aeroplanes, the slower you descend the further out you need to start. Similarly, I understand Green Dot is best Lift/Drag? In that case, Green dot descent point would be even further out. Lower speed = Less drag-> better glide range.
That is, based on your figures, 300 should be 3x+5nm, 250 should be 3x+10nm. Green Dot should be +20nm.
What's your Vnav tell you?
I assume by "+ 20 kts" you mean miles? If so, assuming the A380 flies like most other aeroplanes, the slower you descend the further out you need to start. Similarly, I understand Green Dot is best Lift/Drag? In that case, Green dot descent point would be even further out. Lower speed = Less drag-> better glide range.
That is, based on your figures, 300 should be 3x+5nm, 250 should be 3x+10nm. Green Dot should be +20nm.
What's your Vnav tell you?
Thread Starter
Joined: Jul 2013
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From: Bangkok
Thanks Capn Bloggs 
That was my mistake. I meant NM, not kts 
Just want to have my own rule of thumb instead of 100% relying on the computer-generated DES path or "VNAV" in Boeing world.
Your understanding about green dot is right, but according my figures I didn't mean to use the green dot speed from TOD all the way down to landing. Normally speed is 300 kts, subject to CI and ATC requirement, until approaching 10,000' and then reduces to 250 kts. 300 kts needs longer distance than lower speed to reduce to green dot or S or F speed. That's why!
That was my mistake. I meant NM, not kts Just want to have my own rule of thumb instead of 100% relying on the computer-generated DES path or "VNAV" in Boeing world.
Your understanding about green dot is right, but according my figures I didn't mean to use the green dot speed from TOD all the way down to landing. Normally speed is 300 kts, subject to CI and ATC requirement, until approaching 10,000' and then reduces to 250 kts. 300 kts needs longer distance than lower speed to reduce to green dot or S or F speed. That's why!
Joined: May 2009
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From: Australia, maybe
That is a really odd question.
After you have 'programmed' the arrival the FLT PLN page will give you ToD.
For a 'Rule of Thumb' the aero plane was designed to descend at a 4 times your height profile, and that is pretty much what it does.
After you have 'programmed' the arrival the FLT PLN page will give you ToD.
For a 'Rule of Thumb' the aero plane was designed to descend at a 4 times your height profile, and that is pretty much what it does.
Thread Starter
Joined: Jul 2013
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From: Bangkok
Hi Trent 972, Thanks for your opinion 
What will happen when ATC gives you a radar vector and provides you only expected track miles? I think your programmed F-PLN will no longer accurate. Can you still rely on your TOD or vertical deviation?
From my experience, height profile X 4 is too much for B737, A320, A340 and A380 (LDW 370 T) descending in normally speed (300-320 kts). But it is not enough for A330 as she needs some more NM on top of the height profile X 4.
That's why I'm looking for something more accurate
What will happen when ATC gives you a radar vector and provides you only expected track miles? I think your programmed F-PLN will no longer accurate. Can you still rely on your TOD or vertical deviation?
From my experience, height profile X 4 is too much for B737, A320, A340 and A380 (LDW 370 T) descending in normally speed (300-320 kts). But it is not enough for A330 as she needs some more NM on top of the height profile X 4.
That's why I'm looking for something more accurate
Joined: Dec 2012
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From: Here
You'll be told on your conversion if any difference to your current type, so why not start with what you know? 15 yrs on all big Airbus and 4x height from TOD down to FL150, then start working towards 250kts/ 10000'/ 40nm has always worked for me .Then it's all about distance to run. Be prepared for short cuts and extended arrivals. Start what you know and learn any minor changes from your 380 trainers. Good luck.
Last edited by crwkunt roll; 23rd July 2013 at 05:32.
