Erratic Lateral Guidance During Go-Around

[Skyrideruk 4]

Just tried the new A320/A321 in both FSX + Prepar3D & got his strange behaviour in both sims:

After commencing a go-around, the FMA was blank instead of showing 'GA Track'

After selecting managed NAV, which should have put the aircraft in a turn to the right to follow the missed approach procedure (yes, it was displayed in the MCDU), it actually turned left towards the last known selected heading, even though NAV was annunciated. The aircraft then had a fight with itself, oscillating very quickly left/right/left/right etc. as if it were trying to follow both sets of lateral guidance.

[The Dude 6537]

Which approach was this? When did you go around (alt)? And what GA altitude did you set? I would like to try it on my system.

Thanks

[Skyrideruk 4]

Hi Frank,

It was the ILS DME approach to Rwy 23R at Manchester (EGCC).

Go-around commenced at the Cat 1 DA: 449' baro.

Missed approach altitude set to 3500'

2 autopilots engaged (FMA: Cat 3 Dual). Autothrust engaged.

I've also noticed that there is no 'RW' annunciation in the lateral window of the FMA during takeoff.

I've also noticed this apparent conflict between selected heading & managed NAV modes when overflying a waypoint: sometimes the wings just rock like crazy & you can see the ailerons & spoilers oscillating on the Flight Control page on ECAM as the aircraft attempts to establish on the next leg.

Cheers.

[The Dude 6537]

Thanks for the info I will try the app with GA. I do not really understand the last bit. You are overflying an WP in NAV and it starts rocking its wings? What has HDG got to do with it?

[Skyrideruk 4]

Yes, laterally, the aircraft is in managed NAV mode: sometimes when it overflies a waypoint & starts to turn onto the new leg, there appears to be some confusion in which way it is supposed to be going next: one moment it seems to be turning onto the correct track, but it then starts 'vibrating' in roll, as if trying to deviate from track to follow (perhaps) wherever the heading bug was last set (not in view, of course, since we are in NAV), but at the same time struggling to maintain the flight plan route.

If you check the flight control page on ECAM, you can see the ailerons & spoilers moving in sympathy, i.e. attempting to roll the aircraft one way, then the other, then back the other way & so on.

[The Dude 6537]

hmm, I never seen this behaviour before. I will try the GA now but it is probably linked to the NAV/HDG problem you have.

I will report back with my findings.

[The Dude 6537]

I've also noticed that there is no 'RW' annunciation in the lateral window of the FMA during takeoff.

I do not know if you mean RWY by RW but on my setup it is there:

Now for the go around. Once again all went well on my setup:

You are incorrect about the lateral FMA mode during GA btw. GA TRK is an old standard that is not used on this bus. We modeled the newest systems and those go to NAV as GA mode.

As you see there is no problem with HDG and NAV conflicting on my system. I strongly advise you to de-install and re-install the bus on your computer and hopefully it will sort out your problems.

Good luck!

[Skyrideruk 4]

Thanks for your feedback.

I will do as you suggest & report back...

[Skyrideruk 4]

Okay, just had another go at this:

Sorry, I did mean RWY during takeoff & this time it did appear correctly.

This time the GA was much more correctly flown, with NAV appearing on the FMA (I'll take your word for it about the new standard). However, I noted the following undesirables:

1. At no time did the missed approach routeing appear on the ND, even though it was clearly shown in the MCDU flight plan page.
2. The turn to the right commenced immediately NAV engaged, at approx. 450' QNH, instead of when the aircraft reached the published turn criteria of 750'/D0.0 INN, which was an interesting manoeuvre!
3. The aircraft initially rolled out onto the northerly heading, but after a short time commenced a further turn to the right & continued to do so until I intervened. I'm assuming that it had come to the end of the missed approach routeing & was now looking for another waypoint (still in NAV), instead of perhaps reverting to heading mode. The MCDU shows 'manual' for the routeing at this stage, followed by a route discontinuity, but this is not apparent from what appears on the FMA & ND.
4. On final approach, I understand that that it should be possible to select/preselect a heading & have the heading index in view on the ND + PFD. However, if I try to achieve this, I just see some flickering of the numbers for the current heading in the heading window, which subsequently disappear from view, with no heading marker on the displays.

It's a good job I had an observant PNF!

BTW, I am not receiving any email notification of replies, even though I have selected this option.

[The Dude 6537]

Back again,

1,2,3) That is a known problem with this kind of missed approaches. The way the database and the auto flight is coded in the simulator has some shortcomings. First the 'whichever is later' causes problems and and it does not always do what it is supposed to. Second are the manual legs. These are infinite in the RW and that is also hard to program. If we program them infinite then we have a problem on STARs that have them and therefor we "cut" them "short". This is what you saw in your example. Unfortunately these are shortcoming that we have to life with at the moment. The dev is still looking at the code but when changing one thing it usually causes a domino effect and causes problems elsewhere.

For the time being you could see this explanation as an OEB and fly the bus accordingly. Whenever the auto flight does not do what you want/expect it to do just take over manually. If I would get a dollar for everytime the AP in RL did not start the turn at the correct distance I would be rich now. (ps, this is not meant as a lame excuse for the AP stuff)

4) Yes, this is possible in RL. I never tested it in the sim and also never use it in RL. Why would you if I may ask? I will check it in the sim and forward it to the dev if I see the same thing but do not get your hopes up that it will be "fixed".

Happy Landings!

[Skyrideruk 4]

Thanks for your informative reply.

Regarding 1,2,3): Fair comment. It would be nice if these could be resolved, but I can understand that there are limitations in practical terms.

Regarding 4): I've always though it good practice to keep the heading bug (where available) lined up, in case any other lateral mode which is in use drops out. Also, there may be cases where you are required to fly a specific heading subsequently, such as during a circling approach, or maybe a non-standard missed approach which is not in the data base, or subject to ATC.

Happy landings to you too (& happier night stops)!

[The Dude 6537]

Regarding 4): I've always though it good practice to keep the heading bug (where available) lined up, in case any other lateral mode which is in use drops out. Also, there may be cases where you are required to fly a specific heading subsequently, such as during a circling approach, or maybe a non-standard missed approach which is not in the data base, or subject to

The nice thing about the bus is that it will fly the HDG it had when there is a mode degradation to the HDG/VS. So no need to turn the HDG knob here.

Your habbit is a good one for every plane you fly but do not forget that the heading you "select" will "auto delete" after 50 sec or so, when in a managed mode or ILS/LOC, on the real bus.

[Skyrideruk 4]

I believe that is correct during most phases of flight, however:

I understand that there is also a HDG/TRK PRESET mode which is available before take-off & during final approach/go around, which enables the desired heading to be set, & remain in view, in the heading window on the FCU. In these scenarios, I believe that the heading bug should also remain visible on the displays.

[Skyrideruk 4]

UPDATE:

Hmm, just flown an ILS approach to Rwy 27L at Heathrow (EGLL), followed by a go around:

During this approach, I could clearly see the missed approach routeing on the ND. Also, the go-around was much more precisely flown, with regard to both the vertical & lateral profiles.

At the end of the missed approach routeing, lateral guidance reverted to HDG, with the aircraft maintaining the current heading.

Completely different behaviour to that experienced during the approaches/missed approaches previously flown at Manchester!

[The Dude 6537]

Yeah, most of the time it works like it should.

[Skyrideruk 4]

Going back to post #7: are you sure that NAV engages immediately on commencement of the GA? My understanding is that, with the new standard, NAV will additionally show as armed (not engaged), with GA TRK engaged initially.

[The Dude 6537]

Going back to post #7: are you sure that NAV engages immediately on commencement of the GA? My understanding is that, with the new standard, NAV will additionally show as armed (not engaged), with GA TRK engaged initially.

The basic GA modes are still SRS and GA TRK. But with the new software GA TRK will be active, with NAV armed blue, for less than a second. You can barely notice it and if you blink your eyes at that moment you would never see it. (talking RL here)

Something tells me you have access to a real pilot or simulator

[Skyrideruk 4]

Maybe, maybe not.

Or, could just be a shot in the dark

Thanks for your input , good to get a professional's opinion