Wrong turn in LNAV

jpgmultimodaljpgmultimodal
in Operational questions

Hi,

I have noticed when doing some complicated LNAV approaches with few alternative turns like VNKT RNP 02 or VQPR (Cloud Break) RNP X, Y or Z that, sometimes, when flying LNAV the turn does not start the right way.

Same applies in holds. Here is an example: the LASTI hold at LYTV (could be any published hold).

1 - Outbound leg - OK

2 - Just before the 180° turn, instead of going right, the acft turns briefly to the left.

3 - After few seconds the acft veers right as it should be.

4 - Inbound leg - Ok.

5 - same behaviour than - 2.

6 - same than 3.

You can stay as long as you wish in the hold, it repeats the same behaviour at the beginning of each 180° turn.

I have Win7 - MJC Q400 Pro - Latest patch - P3dv4.5

Thank you if someone could help.

Regards,

JP

Comments

  • kroswyndkroswynd

    JP,

    How goes it? The behavior being exhibited has been a long time nuisance within the FSX and P3D platform where by the aircraft would initiate a momentary turn in the opposite direction before proceeding to its intended path. The Boss was able to minimize its behavior in most cases, but in some other cases it was not quite feasible.

    Here is a quick link to a discussion from a few years ago:
    https://www.fsdeveloper.com/forum/threads/autopilot-turn-opposite-direction.444258/

    I can Have The Boss take another look into it to see if there are any further improvements that can be made.

    Cheers

  • jpgmultimodaljpgmultimodal

    Hi Simeon,

    Thank you so much for your answer. I noticed this behaviour a long time ago but did not know where the origin was. Now it's OK, perfectly understood and there is no need for the Boss to have a look as there are more urgent things to look after at the moment.

    Anyway, most of the time I would do a hold with HDG SEL like when there was no FMS and it works fine, so no worries.

    Keep on the good work and take care,

    Regards,

    JP

  • janar737janar737

    I can add that the same happens when some Radius to Fix (RF) legs in RNAV approaches became active, for example in

    • Salzburg LOWS RNAV (RNP) Z RWY 33
    • Gibraltar LXGB RNAV (RNP) RWY 09
    • Washington Nat. KDCA RNAV (RNP) RWY 19
    • Santos Dumont SBRJ RNAV (RNP) W RWY 02R
    • Queenstown NZQN RNAV (RNP) Y RWY23

    At the moment an radius to fix (RF) leg becomes the active one, the aircraft often rolls first agressively (~15 degrees bank) in the wrong direction and then it start trying to fly the arc as it should.
    Certainly in cases this arc is supposed to bring the aircraft in line with the runway center line for a very short straight in final, it will be hardly possible to safely land the plane.

    See you, Jan

  • jpgmultimodaljpgmultimodal

    Hi Jan,

    You are absolutely correct but, as Kroswynd explained, the problem is coming from the sim itself (FSX / P3D) and there is not much to do for Majectic to correct that.

    The only way, so far, is to follow these LNAVs with HDG select or hand fly and to have higher minima than the ones published.

    Regards,

    JP

  • jpgmultimodaljpgmultimodal

    Hi Jan,

    I had a much closer look at LOWS and as far as I understand we would not be able to execute the RNP Y or Z Rwy 33. Only RNP Visual V Rwy 33 would be allowed if we do not have the special qualification and equipment.

    Same at LXGB: SRA Rwy 09.

    KDCA: River Visual Rwy 19.

    SBRJ: Not allowed and there are quite few alternative procedures for Rwy 02R.

    NZQN: I suppose you mean RNP Z 23. Again special qualification.

    Same applies for VQPR as well as VNKT that I mentioned earlier.

    We could have also mentioned LOWI. Same applies.

    So we have to stick to more "conventional" procedures.

    Regards,

    JP

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