Simviation Forum - Yet another PMDG 737 thread......

Oct 2^nd, 2004 at 7:34pm

zcottovision Offline
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Is it possible to use VNAV descent with the default FS ATC? At the minute I'm using LVL CHG, which sometimes isn't the best.....

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Reply #1 - Oct 2^nd, 2004 at 8:13pm

Nexus Offline
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The PMDG FMC and FS ATC are 2 different things and they can't seamlessly interact with eachother.

The problem with flying with the ATC is that the controller will generally ask you to start your descent too early or even too late regarding to the suggested Vnav Path. I usually disregard ATC commands just to get rid of that problem and contact tower when I'm close to the airport.

AFAIK, you can only fly the azimuth aspect of the route with ATC, but the vertical...that would be impossible I think. And besides, in real life ATC interfers with your descent planning anyways Grin

...not that it helps you though...

I have no problem with LVL CHG (it's almost the same as a VNAV SPEED descent) but just make sure to switch to V/S below 10.000'

« Last Edit: Oct 2^nd, 2004 at 9:27pm by Nexus »

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Reply #2 - Oct 2^nd, 2004 at 11:35pm

Silver1SWA Offline
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The FMC can be programmed to begin VNAV descent whenever you wish. If ATC asks you to descend before the FMC is ready to begin descent, force VNAV to begin descent.

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Reply #3 - Oct 3^rd, 2004 at 12:16am

Nexus Offline
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Quote:

The FMC can be programmed to begin VNAV descent whenever you wish. If ATC asks you to descend before the FMC is ready to begin descent, force VNAV to begin descent.

True Silver, I kinda misunderstood his question...somehow I though he wanted the ATC to comply with his VNAV Path Sad

A capture descent (DES NOW), would be the most easy way I suppose.
Zcotto, you will find that command on the Descent page, and this will intiate a 1000fpm descent until you are intercepting the original descent path
The beauty with this is that DES NOW grants you definite protection from flying through the computed flight path, compared to LVL CHG for example.
You can't go wrong with that one

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Reply #4 - Oct 3^rd, 2004 at 7:06am

zcottovision Offline
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That's pretty much what I was looking for. Now I just have to figure out how to do it!

Also, why the switch to VS below 10,000?

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Reply #5 - Oct 3^rd, 2004 at 7:55am

Nexus Offline
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LVL CHG is so sensitive to speed changes, if you want to lose 10kts, the AFDS will instantly command an agressive nose-up attitude, which sometimes will put you un-necessary high on the vertical path.

If you're noticing that the speed won't drop in V/S mode , simply decrease the V/S and the speed will bleed of..much smoother way of operation, and definetly more comfortable for you and the virtual passengers Grin

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Reply #6 - Oct 3^rd, 2004 at 9:26am

jrpilot Offline
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I find it so diff. to make a descent with the PMDG 737 becasue I always come in to high...then the VANZ discounects becasue it can't reach the altitude constraints I've asked it to complete

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Reply #7 - Oct 3^rd, 2004 at 1:30pm

Nexus Offline
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Junior do the mental math first, are you constraints on the "right" side of the performance envelope, the aircraft must be able to comply with the hard contraints, you know, or else VNAV will disconnect.
Hint: losing altitude and speed at the same time is never easy in the 737.

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Reply #8 - Oct 3^rd, 2004 at 3:14pm

jrpilot Offline
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When I descend 90% of the time VNAV will disconnect and I will have to do a 4000 fpm descent. right away...so what are you saying for me to do...descend earlier?...If I use "descend now" The aircraft only descend at a rate of 1,000 feet per minute...should I use V/S when I use "descend now"...?

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Reply #9 - Oct 3^rd, 2004 at 5:23pm

Nexus Offline
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jr, read the post above regarding "DES NOW" Wink

Yes, it will descent with a rate of 1000ft/min, but just UNTIL you reach the original descent path, then VNAV path will follow the vertical profile, as calculated.

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