VNAV to runway

[dgamble]

Regarding the VNAV to the runway when using the autopilot:

I set up a 3° descent angle, engaged VNAV on the autopilot, and watched in awe as the autopilot guided me down to the runway.

I do have a question, though: once the system engaged for the descent, it replaced what I call the "fly to" altitude in the preselect box to the newly calculated target altitude. What it did not do is level off upon reaching that altitude.

Is that the intended behavior? I can see arguments for both continuing on down as a true ILS would versus leveling at what could be considered an MDA altitude.  I'm just not clear if the behavior I saw was intended, or a result of my using it incorrectly.

 

[KRviator]

Dave's Youtube video of the behaviour. Don't have a beer before watching it, you'll get airsick due the turbulence!

 

[Dynon]

It is the intended behavior. On the IFR side - where the VNAV behavior originated - your "next" altitude should be the one you'll be going to if you go missed. In other words, you don't hang out at your decision height. You have the runway and can continue, or you go missed. Though I suppose you could imagine a more tailored VFR glidepath descent mode that levels off, we try not to have too many inconsistencies in these sorts of behaviors (when you do x, you get y. but when you do (slightly different x), you get z".

 

[dgamble]

Understood - it makes perfect sense

That said, as I thought about the logic and UI of having both modes available, I thought that maybe once I was in VNav mode and descending towards the new altitude in the preselect textbox, pressing the Alt button again would tell the AP that I do want to hold at the (for want of a better term) MDA. That's the way I intercept and hold altitudes now, so it would have felt "right."

This mode would be very useful to VFR pilots. I wonder if it could be configured as a boolean in the settings. I don't think switching between the two would be a common use case - the IFR guys are going to want it to work as accustomed to in their environment, but your larger market, the VFR guys, would likely prefer the level-off mode pretty consistently. And it could also be put in the in-flight setup menu if anyone really wanted to use it in either mode depending on the situation in flight.  You'd probably have to add a mode indicator somewhere, though.

Anyway, thanks a lot for clearing it up for me. It's a good thing to be sure about.

It is the intended behavior. On the IFR side - where the VNAV behavior originated - your "next" altitude should be the one you'll be going to if you go missed. In other words, you don't hang out at your decision height. You have the runway and can continue, or you go missed. Though I suppose you could imagine a more tailored VFR glidepath descent mode that levels off, we try not to have too many inconsistencies in these sorts of behaviors (when you do x, you get y. but when you do (slightly different x), you get z".

 

[preid]

Support;
Using 15.1 the vertical speed required guidance is only overlaid on the VSI when HSI source is set to SkyView. But can it be overlaid on the HSI instead of the VSI? Im learning to look at the VSI, but I sure would prefer to have a horizontal line reflecting the vertical speed required for the destination. It mostly helps see a larger line than a small magenta line on the VSI, which I dont look at much for my descents, especially in turbulence where VSI changes constantly.
Thank you for the consideration.

 

[tomkk]

Is there a way to select a specific runway for VNAV and have that added to the end of the current flight plan? Selecting a runway and pressing "Direct To" replaces the entire flight plan with the single runway waypoint, unless I'm doing something wrong.

 

[Dynon]

Currently, there is not.

 

[airguy]

Currently, there is not.

Do we dare hope that "Currently" might mean this is a temporary situation?

 

[Dynon]

It literally means that that's the way it is right now. It's on our list to possibly change/improve, but that's not a promise.

 

[alexe]

My experience with 15.1 VNAV has been a little different. It consistently leveled off at the preset altitude. However, LNAV consistently tracked several hundred feet left of the extended center line and the runway. I read that HITS might cause that issue, but I have HITS turned off.

Some help and guidance from Dynon clarifying what VNAV is actually supposed to do, as well as addressing the LNAV tracking problem would be appreciated.

Alex

 

[kalewis]

Similar here. With VNAV selected and ALTHOLD on standby it has leveled off at the MDA. And left of centerline ... maybe 75-100 feet.

 

[Schorsch]

Same here by about 60ft and this issue might also cause the HITS boxes to appear as if they are too far to the right...

 

[Dynon]

After VNAV is captured, you should see it re-arm ALT, and the altitude bug will be automatically adjusted to reflect the target you've set up in the deeper setup for VNAV (I thin k1000 feet above an airport, or 400 feet above a runway if you haven't changed the defaults). So it's actually targeting the alt bug, not MDA.

As for the centerline thing - we've seen that too. There might be a bug there.

 

[Savannah_flyer]

Same to me as well, regarding LNAV. It flies about 70-30 feet left of the centerline. It seems like a bug.

 

[dynonsupport]

We have identified that the autopilot doesn't fly the internal LNAV to a runway with as much accuracy as we'd like, so there is a "bug" there.

What we found is that it doesn't simply sit off to the side, but it is "lazy" when within 50 feet of the centerline and doesn't correct the error aggressively enough. This does often look like it's just siting to one side, but it also explains why it could be to one side or the other, or in the center on different approaches or days.

We're working on a fix. Thanks for everyone's input and help.

 

[krw5927]

Dynon, would this same bug also be the reason that, when flying straight-line GPS course guidance from my Garmin GNS480 with autopilot and HITS on, my RV9 often finds itself off to the left by 0.1 or 0.2nm (course deviation as read on the GNS480 display), but when not flying with HITS displayed the deviation displayed on the GNS480 is always 0.0?

I think a couple of us have mentioned this now.

Thanks for looking into it!