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Airbus MCDU Question

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PittsburghLever:
Wow, first one to post ;D

I was watching a cockpit video of an approach to EHAM where the STAR ends in vectors. On the MCDU, I saw that after the last published fix in the STAR, the MCDU showed a waypoint labelled "MANUAL", and immediately after that followed the first point of the final approach. My questions are these:

* For fuel calculation purposes, does the MCDU assume direct path between last published waypoint before the vectors and the first waypoint of the final approach?
* If the above is true, is the vertical path across the MANUAL waypoint assumed to be based on the straight line between the two points?
* Is the MANUAL waypoint something that can be added by the pilots, or is it from the database only?
Thanks!

Trevor Hale:
Hey Boaz.
 
Hopefully Roberto will jump in here soon enough, but in the meantime I will see if I can help you out.  (I use to build an airbus) LOL Then got changed to the dark side. 
 
As far as the MCDU is concerned it will want to fly a direct course from the last fix in the STAR to the "Manual" Fix inputted in the system.  as far as the computers are concerned that is where the plane will want to go.  However, with the vectors the pilots will fly with direct input to the fcu or hand fly the remaining approach as specified by ATC.
 
The Manual waypoint can be added to the MCDU (I can't remember the key sequence) but you basically input the coordinates in the mcdu legs page.  you can create all your own fixes (as with the boeing fmc).
 
To answer your second question, I am trying to picture the layout of the path, but I would think the vertical line you are refering too would be based on the runway heading (If inputted) as a "Reference for intercept for the approach".
 
But maybe I am not following your question.
 
Trev

PittsburghLever:

--- Quote from: Trevor Hale on October 26, 2009, 08:33:34 AM ---To answer your second question, I am trying to picture the layout of the path, but I would think the vertical line you are refering too would be based on the runway heading (If inputted) as a "Reference for intercept for the approach".

--- End quote ---

I guess I didn't phrase it all that well 8) I got a little confused when I read my question again. Here is what I am asking:

Assuming that the MCDU will try to follow a direct (laterally) course between the two waypoints, what will it do in terms of decend profile across the MANUAL waypoint? Will it assume that it has x number of miles (distance between the two waypoints on either side of the MANUAL waypoint) to decend y ft (altitude difference between the two waypoints on either side of the MANUAL waypoint)?

Hope I made my question clear (or, clearer),

Trevor Hale:
LOL, that makes much more sense.  Well when you define the position of the Manual waypoint, you also can specify the "Speed" and "Altitude" to be at when you reach the waypoint.  If you do not specify any, the speed and alt you were at when you hit the last point on the Star will be added to the Manual fix.  However, after it ads the fix, and you modify the speed and Alt, the aircraft will continue to decend on that linear course.  HOWEVER.  if you are operating under "Vectors" as before you will more then likely manage the speed and heading through the fcu as dictated by ATC, and just use the Manual Fix, and the Approach course as a reference.

Hope that helps.

Trev

PittsburghLever:
Thanks Trev, that makes sense!

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