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GamerNurd

perf/vnav unavailable?

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​Trying to make a flight bewteen ESNQ - ESSA and I always get perf/vnav unavailable when trying to engange vnav. In the tutorial flight it worked but not now. I have filled in the perf init page. Don't know what Iam doing wrong =/

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​Trying to make a flight bewteen ESNQ - ESSA and I always get perf/vnav unavailable when trying to engange vnav. In the tutorial flight it worked but not now. I have filled in the perf init page. Don't know what Iam doing wrong =/

 

Make sure the route has no discontinuities!

 

Jan

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​There is no discontinuities. But I haven't selected arrival rwy yet. The route are VAGAS T317 OSK T318 SIPRI N5 HMR.

I have also noticed that in LEGS page FL is 380 when I have selected FL 340 in PERF INIT and CRZ

 

EDIT: Solved. When select arrival rwy the VNAV is working. So you need to select arrival rwy when you are still at origin?

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Hi Joakim,

 

thats why - you need an E/D (end of descent waypoint) - otherwise the FMS has no idea when you want to be "back down" and can´t plan the vertical profile for you. Hence no VNAV available.

 

You could work around it (if you really dont want to enter an approach quite yet) by assigning an altitude to the last waypoint of your route. (this makes that wpt an E/D).

 

Or you could fly the route in other vertical pitch modes (FL CHG, or V/S)...

 

Jan

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Jan, since you're here and x-pilot is down.. is the end of descent waypoint requirement something currently related to your product or something that affects the plane in general? How would you go about entering the route in real life? 

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Hehe, ok, while I am here...

 

having an E/D is also a requirement in the real plane. I am not sure if the plane could fly on VNAV "just for the climb and cruise" - I have never tried that but it might be possible. However, it can certainly not plan a descent if it doesn´t know where (3 dimensions) the descent should end.

 

In the real plane you ALWAYS enter an approach to a runway (or just the runway itself, it serves as the E/D). Then you can change the approach later, if another runway or approach is assigned.

 

If you wanted to fly the 737 to a "general area", then you could place the last waypoint of your route in that area, and just assign an altitude at it. EG: /5000

 

Cheers, Jan

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Vnav is for pussies ;). Raw data 4 evah.

 

;)

 

hahahah, made me laugh!

 

 

In the real plane you ALWAYS enter an approach to a runway (or just the runway itself, it serves as the E/D). Then you can change the approach later, if another runway or approach is assigned.

 

Hi Jan, one question: Is this SOP dependent or is this aircraft dependent?

 

I know for example that in Iberia on the A320 they have the same policy, the route must always be "closed" and reach the destination. If there's an arrival change, just change it in the FMC.

 

However I'm pretty sure I've seen long haul flights (not on the 737, but I believe the 767 or 777) in which due to the length of the flight the crew don't input an arrival until they are closer to their destination and they use VNAV, "just for climb and cruise". I usually do it this way on the 777 and works fine for me.

 

Mit freundlichen Grüssen :)

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Hi Jaime,

 

it could very well be that it is possible to fly VNAV for climb and cruise only. These parts contain no real "path planning" anyway, the plane will simply climb to cruise as fast as it can and then stay there... :smile:

 

We will verify that with a current on-type pilot if we can, then change accordingly - but I consider this a low-priority issue, we have more pressing things on our hands... :Straight Face:

 

Jan

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but I consider this a low-priority issue, we have more pressing things on our hands

 

Eben! Thanks for the reply Jan!

 

I will use FLCH, as Roland amusingly said "vnav for pussies" hahaha :)

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I've been talking to our real world 733 driver over the last couple of days (I really should be editing the 777 Cadet Course, but this has proved a fun distraction) and it seems that in the older Boeings, there is a latent distrust of the VNAV. The reason why the 777 VNAV is much more accurate is because you can download (and continually update) the winds aloft and winds for the descent. The older aircraft such as the 733, 757 and 767, have to make do without this information and as such the VNAV path can be a bit of crap shoot. Many of the crews still flying these old birds revert to FLCH and old fashioned 3 times table to do it, especially once off the LNAV track under radar vectors.  

 

FWIW, I'm mightily impressed with the IXEG and it's the game changer that X-Plane has been waiting for. 

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I've been talking to our real world 733 driver over the last couple of days (I really should be editing the 777 Cadet Course, but this has proved a fun distraction) and it seems that in the older Boeings, there is a latent distrust of the VNAV. The reason why the 777 VNAV is much more accurate is because you can download (and continually update) the winds aloft and winds for the descent. The older aircraft such as the 733, 757 and 767, have to make do without this information and as such the VNAV path can be a bit of crap shoot. Many of the crews still flying these old birds revert to FLCH and old fashioned 3 times table to do it, especially once off the LNAV track under radar vectors.  

 

FWIW, I'm mightily impressed with the IXEG and it's the game changer that X-Plane has been waiting for. 

 

Very interesting points Ben, thanks!

 

I once talked with a 737 NG F/O about VNAV a lot. He told me that "old school" Captains distrust VNAV because of their past experiences with it (early EFIS aircraft), but that given the correct inputs, it works like a charm. He'd say it's a bit of a generational thing and that he sometimes shows his Captain that VNAV can work just fine, the Captains change their pre-conceived opinions.

 

Another thing he mentioned was UPDATING VNAV. That is, when you're inboud to an active WAYPOINT, go to LEGS and input a direct to the waypoint again, and execute. This won't change anything to the route but it will update the VNAV path. 

 

It's funny how this VNAV distrust also happens to simmers. I have been simming for many years and I believe that older VNAVs didn't work all that well, so I grew accostumed to using FLCH, VS and tables of 3 for descents. If I'm completely honest, I cant say how good or bad the VNAV on the PMDG 777 is because I haven't really tried it that much :)

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