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Thread: Vnav question

  1. #1

    Vnav question

    I have a AF-5600, Dynon autopilot, Dynon transponder, Dynon Com and audio panel. No external navigator. I can setup flight plans and crossing altitudes, but nothing I've tried will cause the autopilot to descend to the crossing altitudes. Arming VNAV looks good, but it happily flies the altitude bug right past TOD. VFPL displays TOD and BOD, but won't command the pitch down. I can adjust the bug to the crossing altitude (manually) but I haven't figured out the command sequence to get it to automatically fly the descent.
    Can someone tell me how to get this thing to fly to the crossing altitudes without me changing the bug each time?



  2. #2
    VNAV is only for precision IFR approaches and will remain armed until the capture criteria are met for the selected approach. The EFIS has a special VFPL mode which is what you want to use for enroute vertical flight plan control. There is not a physical button for this on the SV-AP-PANEL, but you can access this mode from the EFIS autopilot page.

    Once this is engaged, go to the EFIS FPL page and here you can enter the altitude profile for each waypoint and any applicable horizontal crossing restrictions. Note that if you do not enter an altitude for a specific waypoint, the EFIS will continue to follow the altitude bug when that leg is active. Also, the EFIS will never descend below the altitude bug even if the VFPL altitude is less than the bug.

  3. #3
    Thank you Jonathon. If I’m understanding this correctly, VFPL only displays the PROMPT to achieve the crossing altitudes I’ve entered in the flight plan. It’s only a prompt because the altitude bug is always the commanding factor for any vertival nav, unless receiving precision guidance from a navigator. This system will not fly a pre-configured descent without manually adjusting the altitude bug AND when the bug is set to the desired crossing altitude, the autopilot immediately follows the bug, not necessarily at the TOD, but as soon as the knob is turned.
    I was very impressed when I saw that I could configure crossing altitudes for each waypoint and the destination. I’m much less impressed now that I know they’re just reminders to re-enter the altitudes into the bug when prompted. I still feel like I’m missing something.

  4. #4
    That is incorrect. With the EFIS in VFPL mode the autopilot will follow the altitudes entered for each waypoint without further interaction. If, however, you fail to enter an altitude for certain waypoints, it will follow the altitude bug for the leg up to that waypoint. The autopilot will not descend below the altitude bug in VFPL mode, so the altitude bug is in effect a sort of minimums bug while in VFPL mode. If the altitude bug is set higher than an altitude you have entered for a waypoint, the EFIS will prompt you to manually lower the altitude bug so as to allow the VFPL plan to proceed as programmed.

  5. #5
    Jonathan! I think I get it!
    I’ll build a flight plan of 4 waypoints, with altitudes. I’ll take off, activate NAV and VFPL and lower the bug to 200’ agl (minimum). It should then cross each waypoint per the specified altitude, with no actions on my part! Right?
    I can live with that!
    I knew I was missing something and you led me through the darkness! Wx is gonna suck tomorrow, but I can’t wait to fly it and try it!



  6. #6
    Update: I'm loving this system! With Jonathon's help, I can now pre-program crossing and terminal descents to my satisfaction.
    I learn new stuff every time I fly.


  7. #7
    How do I exit VFPL mode?

  8. #8
    Switch to ALT mode. One vertical mode and one lateral mode must always be active with the SkyView autopilot.

  9. #9
    I just acquired an RV-10 with 2xAF-5600, Avidyne IFD540 Navigator and a Trutrak Vizion 385 AP. Is it possible to have the AP automatically follow VFPL altitudes either from an internal flight plan on the AF unit or from a flight plan in the IFD540 with this setup?


  10. #10
    Unfortunately VFPL mode requires the SkyView autopilot

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