A320 FMGC Logic

[Last Ditch]

I need some help here..
The other day I was heading merrily to a busy Airport along a STAR and ILS approach inserted.
ATC suddenly asks me to cancel STAR and proceed to VOR of the airport.
I use the direct to function and typed in the VOR.
FMGC deletes all waypoints of the STAR, ILS, missed approach and takes me to the starting point of Alternate that starts from the VOR!! (Is this normal?)
And, just while I was begining to wonder if this is normal, ATC asks me to disregard last and continue with STAR... @@@@!! Can anyone suggest a better way to go about things?
(Luckily my experienced Captain had the presence to recall the Seconadry and get going. And to our good luck the Secondary was not setup for something else e.g. differnt STAR for opposite R/W)
Thanks

[CI54]

Yes, yes.. Been there, done that and u know what else? Had the same solution under the circumstances.

Thing is, was almost caught in the same trap in a Boeing FMC once.. The good thing about Boeing FMC is the appearance of the erase prompt, and that saved the day for me..

[Dalex64]

This very thing was a contributing factor in the AA965 fatal crash.

"FMS logic that dropped all intermediate fixes from the display(s) in the event of execution of a direct routing"

American Airlines Flight 965 - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/American_Airlines_Flight_965)
Cali Accident Report (http://sunnyday.mit.edu/accidents/calirep.html)

[Canuckbirdstrike]

This is standard FMS logic, does not matter which aircraft and whose box. If the direct "to" point is a part of any of the route in the FMS then all points prior to that point are deleted. In this case the VOR was part of the route to the alternate.

And yes been there myself.

[Microburst2002]

hi guys

do you mean that all waypoints in between are erased, including the destination???

[MCDU2]

Happens quite regularly at places like Amsterdam. Your options would be to dial up the VOR into the RAD NAV page and then fly manually towards it correcting for wind in HDG mode or my preference is to go into Trk/fpa. Invariably you will only by tracking towards the VOR for a short time before another vector so having the remaining bits of the STAR is useful for track miles to go and covers you in case the controller changes their mind and gets you to fly the rest of the arrival. Just remember to go back into heading and sequence your flight plan or better still extend the runway centreline to tidy up the plan.

[Last Ditch]

@Microburst2002
Yep, deleted all waypoints (left with waypoints from VOR to alternate)however 'm not sure the destination was still original or alternate... situation developed quickly in descend, weather, thick traffic and struggling control. Also, I am new at this :uhoh:.

@Canuckbirdstrike
My old bird's FMS (based purely on GPS) had a clear distinction between insert function (typed and line selected) and 'cut & stitch' function. Very easy to understand and operate.

@MCDU2 & OK465
Flying to the VOR manually on raw is the option that my Captain debriefed me (I find this hard to believe and thus this post). MCDU2's suggestion of selecting the Bird to nullify the wind changes in descend is taken. Sequencing the flight plan is SOP in our Co on receiving the last vector before arming approach. Sometimes this happens so late, you rather arm approach than clean up (am I right at this?).

Mainly, I hate to think that the FMS can't do it for me without complicating the matter.
Or, am I going wrong somewhere..

[Capn Bloggs]

I'd insert the VOR into the Active flight plan above the STAR and ILS, then go DIR INTC to it. You won't lose the STAR/ILS. Profile will be wrong, of course. If required, you (or the PM:)) can then Lat Rev off the VOR waypoint to set up the new arrival/runway.

Or...As soon as they give you the Direct, Copy the Active (if not already done, as mentioned) then do your direct to.

[Microburst2002]

If the destination remains, there is not much to worry about.

when I "loose" the whole star I just keep flying to the VOR in HDG or with the DIR TO and then make a new DIR tO to any desired point in the sTAR, if they want me to resume it. Not a big deal.
in the mean time I have to make teh VNAV my self, which I like to do anyway...

[rudderrudderrat]

Hi Last Ditch,

I been there and still have the tea shirt.

It all depends on where the VOR (or any point) is, and if you select the "abeams option". If I can't find the place on a sensible part of the FPLAN, then I use "direct to", then HDG towards it, and sort out the problem at my leisure. I don't want another tea shirt.

[capt. solipsist]

create a discontinuity by going direct to some remote waypoint, eg., OSAMA. make sure to pull the hdg knob soon after of course. then go direct to the instructed waypoint, clear OSAMA, and maintain the discontinuity. :}

better yet, just activate secondary :ok:

[OPEN DES]

You cannot use the DIR TO function to fly to a point in the alternate flightplan (it is disabled). You'd have to enable the altn in order to make that work.

Was the VOR you were cleared to overhead the airport? What happened was probably the FMGS going into the done phase thinking that you've landed already. In the done phase everything is dumped. Happens all the time with guys activating the secondary when still not properly established on downwind during circling approaches.

[LOFT]

i think if you enter the vor in the lsk 2L and manage nav (A320), it will create a discontinuity on the mcdu between the VOR and the next wpt of the STAR.
This will allow you to go direct to the vor and still have all the waypoints of the star on the mcdu.

[Big Trevor]

The VOR has probably been hard tuned in the rad-nav page if it's on the field, so is displaying itself on the ND? I'd just do what MCDU2 said and just pull hdg and put your green track line running over it on the ND. You can then tidy up the box to give u the extended centreline or whatever you like. Just keep it simple. You can faff about putting in discontinuities and going dir to and keeping it in managed, but you dont want to be heads down in the box drawing green string all over your ND at this point and u don't know where they are gonna send u after the VOR anyway.

[Last Ditch]

@LOFT
:suspect: My understanding is that... typing a waypoint into 2L lsk (or using next waypoint in Lat Rev) will have the same result as selecting Dir To function... need to check on this.

@OPEN DES
The VOR was overhead the airport, but still if I remember right, about 30+ miles away. However, I think 'done phase' is what happened. And, thank you for the tip on circling approach!! I wonder why 'done phase' dosen't have a better trigger logic?

@Big Trevor
Point taken. What if Control gives me a Hold over VOR?? :confused: I have seen this happen before when Control wants to buy time. Will lat rev from Ppos work? (flying the Hold manually like good ol days is always an option.)


@ALL
Thanks for the input guys.

[0.82]

This reminds me the old and classic OEB 169-2F DUAL FM RESET WITH FIX INFO.

[Microburst2002]

Another option that I often do is just keep in the F-PLN what i think more likely to be the clearance (or expected to fly under radar vectors) and fly to the VOR using HDG. Most of the times I do it, after a while they will give me vectors or a direct to another intersection. So all those times I did't have to reprogram and reprogram again the damn machine.

But you have to take wind drift into account, which sometimes changes dramatically during descent.

[sabenaboy]

But you have to take wind drift into account, which sometimes changes dramatically during descent.

Huh? Ever considered using track/FPA to track inbound to a VOR? :)