VNAV descents and VNAV APP

[arrowspace90]

Ok, so please explain, anyone, how this is supposed to work.  I tried to arrive KDCA and the FRDMM5 arrival to connect to the RNAV to runway 19.  There were no discontinuities.  

First problem was that, between published crossing restrictions on the Arrival and the APP, the FMC would repopulate the in-between fixes with the crusing ALT!  So, FL 370 would be in between 2 crossing restrictions much lower!  Why would it do that?  370 obviously not the altitude that the fMC would "expect" to cross those fixes.

So I took out the 370s and just put in the previous fix crossing alt with a "B" after it, since I cant calculate what it actually is.   I got a reasonable TOD depicted and I put in zero in the altitude window and armed VNAV.  Aircraft did start down and it made the first of the many crossing restrictions.   That was about the only one it made.  The software would show the next expected, lower altitude and it would show a required rate of descent, but it would not start down for any of them on its own with the AP engaged.  I tried to V/S them all, still in VNAV and using the depicted rate of descent.  I probably slightly missed several of them.  

Once I was close in and armed APP, that came on in green.  But again, the aircraft wasn't coming down for me, and I ended up too high to land.  

Yes, I know the real airplane cannot possibly be set up this way.   So, putting in the bottom altitude and being in VNAV and eventually arming APP is not correct?  What is the proper procedure please?  Perhaps in the displays here you can spot an annunciation that suggests what error I am making?

[Pils]

1 hour ago, arrowspace90 said:

Perhaps in the displays here you can spot an annunciation that suggests what error I am making?

Unfortunately there's not really enough context (or quality) in the photos to tell what went wrong. A couple of things from the description you gave:

1. It's not necessary to preselect zero feet for the altitude; the FAF/GS intercept altitude is sufficient.

2. Once in VALT you have to fly at least one dot vertical deviation away from the path before VPATH will capture again, which you have to do explicitly with another vertical mode (FLC, VS, etc.)

3. I can't explain why the cruise altitude would populate the estimated altitude, unless you never reached the planned altitude and the FMS still considered you to be in climb phase.

Is it possible to reproduce and screen record this full flight, and publish a video (preferably in native resolution) to YouTube or similar? Also please post your Log.txt from X-Plane after loading the CL650.

[arrowspace90]

The cruise altitude frequently populates into a descent profile between step downs.  I realize, this is wrong, but I have no idea what the software is doing, or what I could be doing, to cause this??  I definitely did climb to the cruising altitude of 370 and was there for most of the flight. 

I went to V/S on the STAR when the rate of descent suggested went to more than 2500 FPM with the aircraft not starting down.  I'm still not clear on whether or not this should be necessary.  I am a 737 pilot so I only know to put in the lowest cleared altitude in the window and arm VNAV.  I know that there cannot be any discontinuities on the route.  I know that it can't have, inexplicably, the Cruise Alt repopulating the fix crossing altitudes.  

Do you typically have to use V/S on a VNAV descent with this airplane, or should that be necessary?  Often I see PATH go to white instead of green.  Then when I V/S down at the suggested rate, sometimes PATH turns green again and at times it appears to be adjusting to the PATH.  Then not.  Since I don't really know what the airplane in VNAV is "supposed" to do, I don't really know when it is functioning correctly.  Ha.   

Your comments are appreciated.  What does a 737 "LNAV/VNAV" guy need to realize about VNAV descents in this airplane?  Beyond that it is "different"?

Edited January 15 by arrowspace90

[RonMont]

On 1/15/2024 at 11:40 AM, arrowspace90 said:

Do you typically have to use V/S on a VNAV descent with this airplane, or should that be necessary?

No to both questions.

I use VS only in situations where PATH is lost, either because I missed the TOD and need to catch up with the glide path, or if I execute a DIRECT TO that puts me above the glide path.

[arrowspace90]

On 1/17/2024 at 7:00 AM, RonMont said:

No to both questions.

I use VS only in situations where PATH is lost, either because I missed the TOD and need to catch up with the glide path, or if I execute a DIRECT TO that puts me above the glide path.

Ok, thank you, that is good to know.  I feel like I give VNAV every chance, but especially when flying a STAR that has multiple step-down crossing restrictions, I have had issues with the airplane not starting down for the next restriction.  This is with the lower altitude in the window and VNAV engaged.  This is also when all that has been done prior to the TOD.  I fly these same approaches in the Zibo 737 with no issues at all, and from what you say they work the same way.  All the step down altitudes are in the FMC and there are no discontinuities.

[RonMont]

1 hour ago, arrowspace90 said:

Ok, thank you, that is good to know.  I feel like I give VNAV every chance, but especially when flying a STAR that has multiple step-down crossing restrictions, I have had issues with the airplane not starting down for the next restriction.  This is with the lower altitude in the window and VNAV engaged.  This is also when all that has been done prior to the TOD.  I fly these same approaches in the Zibo 737 with no issues at all, and from what you say they work the same way.  All the step down altitudes are in the FMC and there are no discontinuities.

That is very strange; I have never had the issue you describe in the almost 6 months now that I've been flying the CL60 at a rate of about 12-15 flights a week.

Only thing that comes to mind is to make sure that your VNAV is definitely engaged, i.e. not only seeing the VNAV lights lit up in green on the MCP, but actually making sure that the PFD actually shows that it is active (VALTS for example).

 

[arrowspace90]

Well, here's what's happening, though pics may not be perfect.  The photo that only shows the fmc on the bottom right is before takeoff.  I was flying KCLE to KTEB, Cleveland to Teterboro in the snow at both ends.  The arrival into TEB, similar to Newark, KEWR, doesn't have the crossing altitude restrictions built in, the pilot has to look at the plate and plug those in.  So it had LVZ at 18000 and "Mugzy" at 6000.  When I put those in, the fmc inserted 370, the cruising altitude, back inbetween them!  Why would it do that? It does that again and again.  What can cause this? I knew as soon as I saw that that the VNAV arrival was not going to work.  Since I don't know what altitude the box should have put in there, I just typed in 18000B and 6000B respectively.  That didn't work.

In VNAV with the lower altitude in the window and no discontinuities to the runway, the airplane made the first restriction.  But that's the only one it made, it did not even show my 6000 at Mugzi till I was past the FL180B fix.  By then it would have been way too late to make that restriction.  None of the lower altitudes on the ILS were made either, not by the FMC.  I kept V/Sing them in there.  Only on the final segment did the G/S arm.

Anecdotally, I kept looking for the windshield wipers and the bird doesn't have any.  Though looking from "outside" the plane, the visibility at TEB appeared to be over a mile, from the cockpit I could see nothing at all.  The windshield heat was on HIGH.  Since it's "only" a sim, I continued the APP to about 50 feet and used the FD depiction to flare the airplane, which worked.  Something I have never done IRL of course.

I've put some time into learning this little jet.  Not like getting an actual type rating of course. Far from it. I don't have a procedures manual.  I keep thinking that on some flight the light in my brain is going to come on and I'm going to realize what I am doing wrong.  So far, not.

[Pils]

23 minutes ago, arrowspace90 said:

370

That isn’t the cruise level, unless you’re cruising at 370 feet.

[Pils]

22 hours ago, arrowspace90 said:

Though looking from "outside" the plane, the visibility at TEB appeared to be over a mile, from the cockpit I could see nothing at all.  The windshield heat was on HIGH.

If you're using X-Plane 12, Laminar broke the windscreen heating effect, you'll need to use a script to workaround it: https://github.com/pilsnerish/FlyWithLua-Scripts/blob/main/CL650_window_heat.lua

22 hours ago, arrowspace90 said:

Well, here's what's happening, though pics may not be perfect.

I couldn't really tell what you have done wrong from the description or a few poor quality, grainy photos of your monitor. A video, as requested, would have been much more useful. However, in lieu of that, I tried to recreate the flight as best I could, wherein everything worked flawlessly. I made my own video for you to reference: https://youtu.be/n1-LW4nuwN4

I hope that helps.

P.S. Why is your MACH TRIM off at 8,000 feet?

Edited January 20 by Pils

[arrowspace90]

30 minutes ago, Pils said:

If you're using X-Plane 12, Laminar broke the windscreen heating effect, you'll need to use a script to workaround it: https://github.com/pilsnerish/FlyWithLua-Scripts/blob/main/CL650_window_heat.lua

I couldn't really tell what you have done wrong from the description or a few poor quality, grainy photos of your monitor. A video, as requested, would have been much more useful. However, in lieu of that, I tried to recreate the flight as best I could, wherein everything worked flawlessly. I made my own video for you to reference: https://youtu.be/n1-LW4nuwN4

I hope that helps.

P.S. Why is your MACH TRIM off at 8,000 feet?

The Mach trim was an oversight.  I should have seen the yellow alert.  I will watch your video.  Hopefully I will see you setting up something and think, "wow, I wasn't doing that".  I realize this airplane ain't the one I'm accustomed to, but I can be trained if I see where the difference is.  Thanks, would enjoy making this work.

[Pils]

1 hour ago, arrowspace90 said:

The Mach trim was an oversight.  I should have seen the yellow alert.  I will watch your video.  Hopefully I will see you setting up something and think, "wow, I wasn't doing that".  I realize this airplane ain't the one I'm accustomed to, but I can be trained if I see where the difference is.  Thanks, would enjoy making this work.

I hope so, I want it to work for you too. If you have any further questions about what or why I did something then post it here with the timestamp.

Keep in mind I wasn’t using the checklists or virtual first officer, as general procedures weren’t the topic at hand.

[arrowspace90]

Ok, well duh.  When Pils typed "370" as if were three hundred and seventy feet, that jarred me.  I went back to the perf menu and for cruise altitude, instead of typing in "370" as I did in the Boeing, I typed in FL370.  Yep, that fixed the altitudes.  I believe this one thing might solve VNAV in general.  

I saw in Pils video that he knows how to use the all the little pedestal display knobs better than I do.  I haven't used the Jepp plates on screen, and displaying some of the other stuff would be helpful.

Very happy to know why I couldn't see through the windshield. I will fix that right away.  Yeah, once long ago I actually forgot the window heat at night.  I discovered the error at the TOD and immediately turned it on because the whole windscreen was iced over.  Nice move.  The heat managed to melt a hole big enough to see through before the final approach.  I never did that again, but unfortunately I still remember many of the mistakes I ever made while forgetting most of the things I did right.

Edited January 20 by arrowspace90

[arrowspace90]

How do I download Fly With LUA and then how do I plug in this script?   I think I had FWLUA on XP-11 but I forgot how I got it on there, and I don't remember much knowing what to do with it?

[Pils]

1 hour ago, arrowspace90 said:

How do I download Fly With LUA and then how do I plug in this script?   I think I had FWLUA on XP-11 but I forgot how I got it on there, and I don't remember much knowing what to do with it?

https://forums.x-plane.org/index.php?/files/file/82888-flywithlua-ng-next-generation-plus-edition-for-x-plane-12-win-lin-mac/

[arrowspace90]

I have to apply for membership?  I clicked on "download" and that's what comes up.  Wrong?

[Pils]

2 hours ago, arrowspace90 said:

I have to apply for membership?  I clicked on "download" and that's what comes up.  Wrong?

You probably have to sign up for an account, yes.