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Crossbleed
6th Mar 2008, 23:32
When on an intercept HDG to LOC and have say the IF as the next active waypoint, what/how does the PROG page calc. DTG??
My company doesn't believe in tidying up the LEGS page (irritates me no end),and often have several waypoints left behind...what, if any, effect does that have? ( B744 for e.g.)
And to further muddy the waters; If we've been vectored through the LOC and are now heading away from the ILS, what does the PROG page now tell me?

Bruce Waddington
7th Mar 2008, 00:03
Hi Crossbleed,

Leaving useless waypoints in the flight plan page (Airbus) can create several interesting issues.

For instance, if the flight plan page is not cleaned up when radar vectors commence the distance to run will be in error as will the calculations for fuel on touchdown.

If the waypoints left in the flight plan page do not sequence properly on approach and you find yourself doing a missed approach it will be without the proper waypoints on the flight plan page and therefore the managed NAV capability may give you some interesting routing, or none at all. At least until you figure out what is wrong and how to fix it :-))

An acceptable procedure is to delete waypoints until a fix on the approach you will fly over is the to waypoint and PPOS is the from waypoint. The FMGC then calculates the distance to go and the fuel based on present position direct to the to waypoint. And it gives you a good navigation picture on the ND.

best regards,

Bruce

EMIT
7th Mar 2008, 07:45
Hello XBleed,

Also in a Boeing, it is like the previous poster states: distance from present position to active waypoint and then the route along the string of waypoints to destination.
Whether the FMC/FMGS just takes straight line distance from PPOS to active waypoint, or whether it makes an allowance for turn circle, I am not sure of.

When being vectored to final, the most convenient way to clean up the waypoints is to create an intercept leg to the glidepath intercept waypoint.(Airbus drivers, don't forget to disarm NAV). In that way, NAV or LNAV will be available for missed approach guidance.

Crossbleed
7th Mar 2008, 09:09
Thanks for the replies guys, I assumed the PROG page extended a line to the extended centreline with an excecuted INTCPT CRS from PPOS and maybe assumed a rate one turn at current speed onto that magenta line....My gripe is that on approach my people are leaving all sorts of old waypoints lying aroung and don't bother X-checking DTG at anytime. Without an alive GS I get blank looks when I suggest they're a bit low etc...
The absence of a Boeing FCTM in English make it harder to make my point.

potkettleblack
7th Mar 2008, 12:43
On the Airbus 320 we clean up the flight plan to delete any unused waypoints. We do this generally as we pass over or abeam them or it is clear we won't be going near them when the controller has given us a heading to fly. Then when we have a fair idea that we will get vectors for base or onto an intercept heading for the final approach course we will clean up the entire flight plan by going direct to the centre fix shown in the plan and checking that the radial is the extended centre line of the runway. This gives a nice picture to help with your situational awareness and particularly at airports with parallel approaches is a good reference to ensure you don't go blasting through the localiser course. You also need to pull heading so that it doesn't go into NAV mode and voila the track miles should be more representative. Also I usually have the runway in the progress page so that it gives me distance to the threshold as a further check and I flick between the flight plan and progress pages to keep an eye on my distance. Usually you will also have a DME as a further backup on the ND as well.