A320 AP/FD modes misbehaviour

  • Hello.

    I just wanted to point out something I think is erroneous regarding AP/FD modes displayed in FMA (upper area of PFDs), after creating a flight plan to be flown in managed modes:

    - When starting the takeoff run, vertical mode SRS is properly engaged, but lateral mode should be RWY (or RWY TRK provided there is no ILS associated to takeoff runway) instead of blank until CLB mode activates at ACC ALT.

    - When a heading is preselected before takeoff, likewise RWY (TRK) should be active during takeoff run but HDG mode is in blue below, waiting for pilot to pull HDG knob to activate it. In AF2, HDG mode becomes active just after liftoff, which is incorrect as aircraft might begin a roll at a very low altitude.

    - When in flight if I make a DIR TO towards a waypoint, it seems to me that F-PLN from that waypoint disappears (I have to check it again anyway).

    - Otherwise I tried to use the new feature for suggested ALT CRZ by clicking the corresponding LSK in MCDU, but when I insert it there is no reflection in FCU ALT window nor PFD display.

    Best regards.

  • We have tried to follow the FCOM as closely as possible. There, if I remember correctly, it says that RWY TRK follows a RWY mode when there is no NAV mode armed after takeoff. So to my knowledge RWY TRK only activates if RWY has been active. And for that you require a LOC signal.


    Also to my knowledge you can engage HDG on the ground, it does not arm, it goes straight to active mode. But we have yet had a real world pilot confirm this. Nobody does this in the real world... I know that rotating the heading knob kicks out armed NAV mode on the ground. Not sure what happens if you pull the knob though.


    HDG is the basic lateral mode, so it has to activate in the air when there is no other mode. Also this is implemented to the best of my knowledge, interpreting the FCOM and reading between the lines here. If RWY TRK is active then we would not have to use HDG right away. On automatic engagement the heading synchronizes to the present heading, so no turn is commanded by the flight director.


    If you are a real world A320 pilot and can verify that these things are as you say in the real world aircraft then we can of course adjust this. The FCOM does not mention these edge cases and I would be happy to learn how it actually behaves.


    I've also looked at other A320 add-ons for other simulators, some of which were quite expensive ones. They model these mode changes exactly like we do.

    I have not looked at the MSFS A320 mods so far.


    The DIR TO page is not fully implemented yet, the route does not actually create a direct to when I tell it to. Sadly it deletes everything instead, nothing I can do here, sorry. We'll have to wait until the programmer of the route has their desk free again for this.

  • Quote

    Also to my knowledge you can engage HDG on the ground, it does not arm, it goes straight to active mode. But we have yet had a real world pilot confirm this. Nobody does this in the real world... I know that rotating the heading knob kicks out armed NAV mode on the ground. Not sure what happens if you pull the knob though.


    HDG is the basic lateral mode, so it has to activate in the air when there is no other mode. Also this is implemented to the best of my knowledge, interpreting the FCOM and reading between the lines here. If RWY TRK is active then we would not have to use HDG right away. On automatic engagement the heading synchronizes to the present heading, so no turn is commanded by the flight director.

    Hi Jet-Pack.

    I enclose an excerpt from FCOM where explains HDG PRESET mode before takeoff. In fact, there are SIDs that tell the pilot to keep a given heading after takeoff until a certain altitude (for example) and then resume managed navigation by going straight to a F-PLN waypoint (DIR TO). Before activating HDG mode after takeoff, RWY TRK mode is kept and appears in FMA.

    Please check with a real pilot.


    "The system has a HDG/TRK preset function for takeoff and go-around.

    If the flight crew chooses not to fly the flight plan after takeoff or go-around, they may preset a HDG or

    a TRK on the FCU by turning the HDG/TRK knob. The value they set remains displayed in the FCU

    HDG/TRK window until they pull the knob.

    OPERATION AT TAKEOFF

    HDG/TRK preset is available before takeoff and up to 30 ft RA. Turning the HDG/TRK knob before

    30 ft sets the desired HDG/TRK. As a consequence:

    - NAV is disarmed

    - At 30 ft, RWY TRK is annunciated until the HDG/TRK knob is pulled.

    OPERATION AT GO-AROUND

    Whenever the LOC*, LOC, LAND or GA modes are engaged, the HDG preset is available. If the

    flight crew rotates the HDG/TRK knob to set the value, it will remain displayed in the window. Pull

    out the HDG/TRK knob to activate the mode and turn the aircraft to the preset value.

    When overflying the MAP, HDG/TRK will synchronize with the current value. The HDG/TRK preset

    function is no longer available.

    CANCELLATION

    The flight crew can cancel a preset HDG/TRK by:

    - Engaging the NAV mode using the DIR TO

    - Pushing in the HDG/TRK knob (arming NAV mode)

    - Disengaging AP/FD."


    Quote

    We have tried to follow the FCOM as closely as possible. There, if I remember correctly, it says that RWY TRK follows a RWY mode when there is no NAV mode armed after takeoff. So to my knowledge RWY TRK only activates if RWY has been active. And for that you require a LOC signal.

    Yes, I think you are right. Except that RWY TRK activates at 30 ft if there is a HDG PRESET before takeoff, until pulling HDG knob to activate HDG mode.


    Quote

    Otherwise I tried to use the new feature for suggested ALT CRZ by clicking the corresponding LSK in MCDU, but when I insert it there is no reflection in FCU ALT window nor PFD display.

    Please check what I am doing wrong here.


    Sorry for my questions, I like your A320 and would want it to be as realistic as possible.

    Best regards.

  • I'm not sure what the current release version of the route does with the cruise altitude entry. My developer version is almost half a year further by now, so things will probably behave different on your end than what I am seeing and what may become available with future updates.


    When the cruise altitude is entered and the aircraft captures that altitude the vertical mode should change from ALT to ALT CRZ. I'm not sure if it does that when the altitude is already captured and you enter the cruise altitude after that. I may have to look at that case, too.

  • Hello. My version is of the end of January.

    What I read somewhere in the changelog is that you can change (on ground) the ALT CRZ in the MCDU by clicking the corresponding key adjacent to value shown in PROG page. Doing so and inserting the suggested value (or any other), it is only reflected in MCDU and not in FCU window, and apparently is ignored. Maybe I am doing it wrongly.

    Regards.

  • Hello, Jan.

    Sorry to insist on this. IMHO I can confirm after googling and checking other sources that HDG PRESET function is not correctly simulated: in real aircraft when the pilot preselects a heading prior to takeoff by turning the HDG selector (but without pushing/pulling it), that heading keeps preselected. After liftoff at 30 ft the RWY TRK mode activates (to keep the runway axis) until pilot pulls HDG selector, in that moment HDG lateral mode activates.

    In AF2, there is no RWY TRK mode but instead HDG mode activates after liftoff without pilot input, and the plane would make a roll at such a low altitude. Not realistic.

    Just for info.

    Regards,

    Ricardo