A320 DPO
Joined: Aug 2017
Posts: 80
Likes: 3
From: Somewhere
What is that??
I fly the 320 and have never heard of it. Best thing would be to descend in accordance with ATC instructions and if the green dot on the side of the altimeter scale is in the middle everything is working as it should.
I fly the 320 and have never heard of it. Best thing would be to descend in accordance with ATC instructions and if the green dot on the side of the altimeter scale is in the middle everything is working as it should.
Joined: May 2001
Posts: 1,424
Likes: 34
From: London,England
Joined: Aug 2007
Posts: 289
Likes: 2
From: The Netherlands
Idle or Idle
From what I recall of A-320 descent - it is calculated with (increased) idle, as if engine anti-ice is ON all the time - this out of concern by Airbus that they don't want you to have an excess of energy at the bottom of your descent, if they would calculate with minimum idle, and you would need engine anti ice during the descent.
This means that usually you will end up with too little energy at the bottom of your descent and thrust will be added (automatically) if you reach the bottom of the (descent) speed margin.
I gather from the DPO snippet of information, that a new descent profile calculation is invented, where the figures for descent thrust will be more accurate to real world usage of low idle, the margin to cater for excess thrust will not be so large anymore.
In a Boeing, they used to calculate the other way around - real idle as standard, and increased (anti ice) idle below the pilot entered flight level for (expected) anti ice usage.
In the 787 however, VNAV descent now uses slightly more than (real) idle thrust for the whole descent. Now the fanatics on environmental fuel consumption can stay level a bit longer than the VNAV Top of Descent and try to fiddle an idle descent in FLCH.
This means that usually you will end up with too little energy at the bottom of your descent and thrust will be added (automatically) if you reach the bottom of the (descent) speed margin.
I gather from the DPO snippet of information, that a new descent profile calculation is invented, where the figures for descent thrust will be more accurate to real world usage of low idle, the margin to cater for excess thrust will not be so large anymore.
In a Boeing, they used to calculate the other way around - real idle as standard, and increased (anti ice) idle below the pilot entered flight level for (expected) anti ice usage.
In the 787 however, VNAV descent now uses slightly more than (real) idle thrust for the whole descent. Now the fanatics on environmental fuel consumption can stay level a bit longer than the VNAV Top of Descent and try to fiddle an idle descent in FLCH.
Joined: Mar 2001
Posts: 4,563
Likes: 35
From: I wouldn't know.
That explains quite a bit actually, always wondered how the bus handled anti ice, whereas the 737 required the input to correctly calculate VNAV. As the bus is not as aerodynamically clean and descends much better though, i never really cared. It is so damn easy to get it down compared to the 737, i found it always more than easy to get it to where i want it to be.
Joined: Jul 2006
Posts: 1,100
Likes: 111
From: Somewhere over the rainbow
I noticed the TOD arrow is usually quite conservative assuming correct winds have been insterted and no anti ice systems used. I usually wait to cross the TOD arrow and when it disappeared and FMA displayed “T/D reached” or “deccelerate” on the older version then only I initiate the descent. It goes immediately to idle thrust slightly faster than the target speed for a little while then usually settle again nicely to the target speed. I love those idle segments.
Good question and I’m not sure either. Would be cool if someone can bring some lights on this one. = )
Good question and I’m not sure either. Would be cool if someone can bring some lights on this one. = )
Joined: Oct 2010
Posts: 422
Likes: 5
From: 5° above the Equator, 75° left of Greenwich
*Using a combination of selected modes and speed brakes, depending on the airport. My 2c.
Particularly true for STARs with some amount of constraints.
Out of pure observation I reckon it's done with current wind + current modes and values selected. I've noticed it's accurate enough whether with descent winds inserted or trip wind inserted in init B.
Originally Posted by Sidestick_n_Rudder
I figured out long time ago, that the Bus Vnav is cr@p
Originally Posted by Spudder
Just out of interest, the blue level off arrow when in HDG. Is that computed using the inputted decent winds, current actual wind or still air?
