Experiencing more VNAV issues.

[airfrance]

I feel like ever since I bought this plane, as well as what I've seen other people say, the VNAV on this airplane, mainly on decent is just not working like it should compared to flying other 737s. Calculating the top of the decent 60nm away from the airport and it rarely follows the VNAV profile. The legs show it should be at a specific altitude but it never started descending. Or the VNAV path is all screwed up. Constantly being too high or too low. Is there any kind of fix planned for the fairly poor VNAV or is this it? 

[airfrance]

Should be at 5,000 feet and I'm still at 22,000 feet in level change mode. Airplane incorrectly calculated the VNAV and never started descending properly. Now that it's caught up, it's over 13,000 feet high and I'm gonna have to make a big circle to lose altitude. If this was a new thing, I probably wouldn't post it but it's a constant issue, time and time again with the IXEG 737. Google IXEG and VNAV and a bunch of stuff comes up. There are several 737s to choose from that don't behave this way so I feel confident in saying that it's something with the coding or whatever. But it's never fixed. 

Also wondering why it's not flying the speeds on the FMC? Not in this picture but often times, it won't fly the commanded speed in the FMC. I'm just feeling like I'm finding many bugs with the FMC, A/P, VNAV, etc. After 4 years and after flying other 737s. I'm trying to grasp why the IXEG 737 is the way it is.

Edited August 19, 2020 by airfrance

[airfrance]

FLATI1 arrival for DEN rwy 34R. The VNAV is calculating the T/D as being literally when I'm over the airport. From FL350. This is not correct at all.

[Litjan]

Wait, you are saying that VNAV doesn´t work correctly for the descent??

That being said, it could be very well that the calculation is correct, I would need to see the miles remaining on your PROG page to judge that.

 

Edited August 19, 2020 by Litjan

[airfrance]

12 hours ago, Litjan said:

Wait, you are saying that VNAV doesn´t work correctly for the descent??

That being said, it could be very well that the calculation is correct, I would need to see the miles remaining on your PROG page to judge that.

 

Okay. I missed this thread. Sorry, there's a lot of information on sites like these and sometimes you miss something. Anyways, I digress. So you are aware that there are VNAV issues on descent. That's more or less what I was curious about. VNAV climbs the plane very well. It's just the descent that is the issue. I'll be honest.. like most I fly other airplanes as well but love the IXEG. So when I come back to it, it's easy to forget little quirks it has. But I suppose the VNAV issue was something I never really noticed before. Maybe I've always gotten lucky with approaches that didn't have all the restrictions. I'll just have to change how I fly it is all. Having the knowledge of this will help in the future.

I didn't see on there if the VNAV issues are supposed to be fixed. I know it's a list of things that still need to be worked on and what is high priority but after the VNAV, you don't have anything regarding a timeline on when/if it's getting fixed. 

And to answer your question, the T/D was calculated to start 33nm away from the destination (DEN) and E/D. From 35,000 feet. At first I thought maybe it was because there was no PERF information yet and it would recalculate once the CRZ ALT was entered, etc... but it never did. So I had to manually descent when the PROG page showed about 100nm away. Then I used the green arch and V/S to match where I needed to be according to the approach charts. Sometimes the VNAV would randomly catch up and I would be able to use it but as soon as it lost the profile, which it always does, I reverted back to my method. - Not ideal or how it would be in real life as a 737 would almost always use VNAV for descent but for the IXEG, my method will have to do until/if you guys fix it.

Edited August 19, 2020 by airfrance

[Cameron]

I suggest you have a read through these forums about VNAV, why it is the way it is, and the fact that the following is also not entirely true:

"Not ideal or how it would be in real life as a 737 would almost always use VNAV for descent..."

Plenty of information to the contrary about this, specifically with the Classic. @Litjan was a Captain on this aircraft for many years. VNAV just wasn't a thing in daily life, and he explains reasons why when it comes to this specific aircraft in various threads.

That said, yes, VNAV has quirks. This is also why I suggest you read around. It's not something hidden by any means.

[Litjan]

Hi airfrance,

yes, I try to keep that post up-to-date as much as possible. Your observation is spot on - the VNAV climb and cruise works good (except for some small quirks, like being unable to input manual speeds), and the VNAV descent works if there are no restrictions on it.

We will work on the VNAV after this next small patch (1.33) is out.

I guess it may depend from airline to airline, but at my airline VNAV was basically NEVER used on descents in the 737 classic. It may be different for NGs and at other airlines, but the VNAV descent on the Classics was a bit quirky (not as much as ours is, though!).

Thanks for the nice words about our plane!

Cheers, Jan

 

[airfrance]

7 hours ago, Litjan said:

Hi airfrance,

yes, I try to keep that post up-to-date as much as possible. Your observation is spot on - the VNAV climb and cruise works good (except for some small quirks, like being unable to input manual speeds), and the VNAV descent works if there are no restrictions on it.

We will work on the VNAV after this next small patch (1.33) is out.

I guess it may depend from airline to airline, but at my airline VNAV was basically NEVER used on descents in the 737 classic. It may be different for NGs and at other airlines, but the VNAV descent on the Classics was a bit quirky (not as much as ours is, though!).

Thanks for the nice words about our plane!

Cheers, Jan

 

Thank you for your engaging response with the community. If I came across as rude in my original post, that was certainly not my intention. As we all know, it can be very hard to judge tone and other things over text.

Like I said, having this knowledge will help me fly the 737 Classic better. It's another difference from flying the 737NG that takes a little getting used to. Obviously many 737 pilots started off on the classic before moving to the NG so all the little quirks and differences wouldn't have been anything foreign. - I'm sure you can speak to this if you're still flying the 737 today.

Your product is in my top 5 favorite ever produce for X-Plane, despite the little bugs and imperfections. And after 4 years, I love seeing that you guys are still trying to keep it updated. (I won't name names but another big producer of X-Plane aircraft should be taking some notes...) I hope to see you guys keep this product alive as long as you can, maybe even taking it a step further with different varients, updated model taking advantage of new XP technology, etc. It's a marvelous airplane and very fun to fly. 

[Litjan]

48 minutes ago, airfrance said:

I'm sure you can speak to this if you're still flying the 737 today.

Unfortunately my airline phased out the 737 Classic about 5 years ago and we didn´t get NGs or MAX as a replacement. I was transferred to the A320 family, which I personally do not enjoy flying as much as I enjoyed the 737.

Yes, we intend to keep the IXEG 737 current and relevant as X-Plane progresses, and once it is "feature complete" we will look into expanding its scope as well.

Cheers, Jan

 

[airfrance]

18 hours ago, Litjan said:

Unfortunately my airline phased out the 737 Classic about 5 years ago and we didn´t get NGs or MAX as a replacement. I was transferred to the A320 family, which I personally do not enjoy flying as much as I enjoyed the 737.

Yes, we intend to keep the IXEG 737 current and relevant as X-Plane progresses, and once it is "feature complete" we will look into expanding its scope as well.

Cheers, Jan

 

Well that's no fun! Of course I've only flown the 737 in XP but I can say I prefer the NG over the classic just because of all the upgraded features that the classic can't do, like no speed intervention. Gosh I wish the classics had that. But I also love the classic so I manage. It makes it more fun to change between types. Flying a 300 classic one flight and a 900ER NG the next. Everything is pretty much identical as far as flows go. Just a few differences.

I fly the Airbus in XP as well (A319-A321) so I guess I'm "type rated" on the 737 and A320 although that doesn't really exist in XP. But the two are equal but also very different. Like I've been amazed how much runway the small A319 actually uses up under certain conditions. Same with the 737. 12,000 foot take-off rolls on the 737-800 are not uncommon! Haha... anyways, this forum is for the 737, not the Airbus. 

Edited August 20, 2020 by airfrance

[Litjan]

5 hours ago, airfrance said:

that the classic can't do, like no speed intervention.

The later Classics even had speed and alt intervention - we chose to model the earlier variant because it is easier .

But I have never in my life pressed those buttons on the aircraft that had them - I know what they do from the manual, but that description was just a little vague...too vague to try this with a real aircraft, I guess .

I think those buttons got about as much use as the "expedited climb" button does in the 320s...

Cheers, Jan

 

[airfrance]

19 hours ago, Litjan said:

The later Classics even had speed and alt intervention - we chose to model the earlier variant because it is easier .

But I have never in my life pressed those buttons on the aircraft that had them - I know what they do from the manual, but that description was just a little vague...too vague to try this with a real aircraft, I guess .

I think those buttons got about as much use as the "expedited climb" button does in the 320s...

Cheers, Jan

 

Haha... I can't ever think of a reason to use expedited climb on the bus unless you really needed to do as quick of a climb as possible but I feel like OP CLB does the same thing. It's going to climb and descend the plane at the fastest rates. I've noticed some A319-321s have had that button removed or had an INOP sticker added.

Like I said, speed intervention on the 737s that have it is certainly a nice feature. Probably the best part is for an approach where you want to fly faster than the published speeds. Or even the flaps speed. If ATC tells you to fly 180 knots even though the published speed is only 160 for example. Or maybe you want to start setting approach flaps but still want to keep your speed up. Considering you can fly something like 220 knots with flaps 5, you can use the speed intervention for that, although I don't know why you'd want to as the higher speed is going to make it that much harder to get down. Anyways, I like that the classics have the quirk of not having this. It makes me appreciate it more when I fly the NG.

[Litjan]

4 hours ago, airfrance said:

but I feel like OP CLB does the same thing.

The difference to EXP CLB is that OP CLB will climb at the speed you have set on the FCU. EXP CLB will pull the nose up to green dot, converting all kinetic energy into altitude, then climbing at green dot (best angle).

It is a pretty violent (for passenger jets) maneuver, I have tried it on a ferry flight - but using OP CLB with the speed dialed back to green dot would accomplish the same thing, just a bit more smooth.

Cheers, Jan

 

[airfrance]

19 hours ago, Litjan said:

The difference to EXP CLB is that OP CLB will climb at the speed you have set on the FCU. EXP CLB will pull the nose up to green dot, converting all kinetic energy into altitude, then climbing at green dot (best angle).

It is a pretty violent (for passenger jets) maneuver, I have tried it on a ferry flight - but using OP CLB with the speed dialed back to green dot would accomplish the same thing, just a bit more smooth.

Cheers, Jan

 

Yeah that's what I figured. I always fly green dot speed in OP CLB or OP DCT...

While I have you... I want to upgrade to the newer version of Gizmo 64 and wondering if there's a way to do that without having to reinstall the whole airplane. I always just check to install the stable version but I haven't seen anything regarding issues with the new one (that says is in beta) and would like to give it a try to see the performance increase. With the current version, I still get little micro-stutters which I think the new version of Gizmo is supposed to fix. I just didn't want to create a new thread just for this.

Edited August 23, 2020 by airfrance

[Cameron]

2 hours ago, airfrance said:

While I have you... I want to upgrade to the newer version of Gizmo 64 and wondering if there's a way to do that without having to reinstall the whole airplane. I always just check to install the stable version but I haven't seen anything regarding issues with the new one (that says is in beta) and would like to give it a try to see the performance increase. With the current version, I still get little micro-stutters which I think the new version of Gizmo is supposed to fix. I just didn't want to create a new thread just for this.

https://www.x-aviation.com/downloads/Gizmo_Updater.zip