Airbus320 <Track mile computation in HDG mode>

[hangil94]

Hi, I'm kinda newoo~ in Airline pilot, and my first assignment is Airbus 321(320) .... ^^

My question is ....

When ATC gives me Radar Vector to final course, I pull HDG and
set the assigned heading.
and if I do that, I recognize track miles in MCDU change, sometimes.....

How can I interpret these track mile figures in HDG mode????

I asked to my co-workers, but I didn't get apparent answer..

Plz, give me the answer ^^


Have a nice FLT !!

[KC-10 Driver]

I'll get back to you after my next flight...

[Artificial Horizon]

As I understand it when you go into HDG mode then the MCDU track miles is still assuming that when you go back to NAV mode you will return to the 'TO' waypoint and carry on the original track. If you don't keep updating the 'TO' waypoint to keep it in front of you then the track miles will over read as the FMGC will calculate the distance back to the 'TO' waypoint even if it is now 100nm behind you!! So the secret is that if you want to keep the track miles accurate then keep sequencing the 'TO' waypoint to ahead of you.

[TopBunk]

....and another one for you wizards out there.....

When the STAR includes an unterminated 'manual' leg, how does it (correctly) calculate the track miles and fuel?

As an example Copenhagen 22L with a non-terminated track off KOR, with no link to the FAP/FAF.

Does it just assume an abeam FAP/FAF point and create (without showing) a base leg?

[joe]

For the last one you could always put in a place / bearing / distance (PBD) into the fmgc. You don't have to let the box fly it but it will give a more accurate track distance and fuel figure!.

Rgds Joe

[TopBunk]

joe

you misunderstand, I DO put in a pbd.

What I asked was what logic the fmgc uses to seemingly come up with the correct answer given that there is an unterminated 'manual' leg. I guessed that it uses some sort of hidden pseudo base leg position to do with the FAP/FAF.

[TAVLA]

The FMGS assumes you will turn onto final approach abeam the Final Aproach Course Fix for the approach loaded for track miles and fuel calculations.

This will be the CF, CI, CL, CB, CD, CV, CS, CN, CQ, CM or CR in the specified aproach.

For instance, an ILS my have a position CI27R.

This is why the miles indication at the bottom of the Flight Plan page is the best indication of track miles in the descent.

Incidently this doesn't work with the A340-200 (and I am guessing a few other older FBW airbusses) if a track offset has been inserted (software problem.

Hope this makes sense and helps.

Regards