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Capt. Windh

VNAV or LVL CHG on Descent?

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Just a quick question. When should I descend with VNAV and when with LVL CHG? I figured that it should be LVL CHG all the way, but then, maybe it should be VNAV when the T/D has been passed and the FMC "wants" me to go down... And another thing.. How come my EICAS always says "CRZ" when I


/Johan Windh

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Guest Erups

VNAV is generally advisable if and when you have a complitely layed out route, with altitude constraints.The computer will dinamically calculate your path according to the points you inserted (bugs apart, as there is one just in the Vnav).Lvl Chg is a "manual" vertical mode, commanded mainly by speed.Regarding N1 Limits: there are no specific limit for the descent phase, so the FMS automatically uses the Cruise option.

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>When should I descend with VNAV and>when with LVL CHG? I figured that it should be LVL CHG all the>way, but then, maybe it should be VNAV when the T/D has been>passed and the FMC "wants" me to go down... >If you ever watch some DVD video shot from a deck of a real aircraft you would see they use all the modes (LVL CHG, VNAV SPD/PATH, V/S) in descent depending on the situation. Michael J.WinXP-Home SP2,AMD64 3500+,Abit AV8,Radeon X800Pro,36GB Raptor,1GB PC3200,Audigy 2http://www.precisionmanuals.com/images/forum/747400.jpg


Michael J.

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Guest Erups

>Well I

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>configure the MCP to get what you expect, ie to arrive over>that point at a certain altitude with a certain speed.This is the key. Any sim-pilot should subject himself to a test of a really busy arrival (say Golden Gate 4 at KSFO) with lots of ATC interaction. There is simply no way you could use VNAV at this point and even limiting yourself to just LVL CHG would be probably too restrictive. You have to know the aircraft very well and be able to handle whatever is thrown at you. No excuse "sorry, but I thought XXX mode is not to be used in this phase".Michael J.WinXP-Home SP2,AMD64 3500+,Abit AV8,Radeon X800Pro,36GB Raptor,1GB PC3200,Audigy 2http://www.precisionmanuals.com/images/forum/747400.jpg


Michael J.

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Guest Erups

>This is the key. Any sim-pilot should subject himself to a>test of a really busy arrival (say Golden Gate 4 at KSFO) with>lots of ATC interaction. There is simply no way you could use>VNAV at this point and even limiting yourself to just LVL CHG>would be probably too restrictive.Rome TMA is also very busy, and i usually fly online.Thursday evening is Online Day in Italy, and you bet there is more traffic on Ivao then at the real Lirf ;)In those cases i could revert even to V-speed or switch to manual and go speadbreak galore!It all depends on the traffic flow: it can delay you a lot.Anyway Vnav is known to have a (pretty bast_ard) error in the descent, where in case of (multiple) altitude constraints after one the AFDS will not reset itself to descent, and hold a shallow dive of about 500ft/min.It may happen that you don't notice until it's too late... (happened...)

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I use VNAV PATH for all descents to 3000' and then intercept the LOC and then the GS. But I rarely use ATC, so nobody restricts me for traffic purposes (great to have TCAS!). But if I were in a really busy area with a lot of ATC, I'd never use VNAV; I'd use LVLCHG or SPD/VS mode. LVLCHG tends to tip you over rather steeply and you can hit -3500 fpm or more quite easily which is pretty darn fast. I prefer SPD/VS mode for that reason.Actually, to be honest, I can't figure out how to use VNAV quickly and flexibly during descent along with other descent modes. VNAV remains somewhat confusing to me no matter how much experience I get with it.Jonathan


Jonathan Sacks

Dell XPS Gen 4, Pentium IV Northwood extreme 3.8Ghz, 3Ghz RAM, eVGA 7900 GTO,

12 GoFlight modules plus MCP-PRO AP and EFIS, GF pedestal, CH rudder pedals,

CH throttle quadrant, 42" LG LED, 24" DELL LCD, Windows XP, FS2004, FSUIPC 3.96

FS Autostart 1.1 (Build 11), FS Navigator 4.6, UT, FE, GE, REX, PMDG, Level-D, PSS, etc.

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Guest Knikolaes

What is an "autopilot" anyway?Just kidding.Manual rocks, but I agree as well, learn the AC as much as you can. 50,000 touch-n-go's at a regional airport is a good start (that numkber being a figure of speech of course LOL).Chris

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Guest tmetzinger

I spoke with a southwest pilot on their descent profiles. Without an autothrottle, they generally use VS for descents and manage forward speed with the throttle. They find this to be a more passenger-friendly ride than using LVL CHG and managing descent rate with the throttle.When using VS, you should have the FMC DES page up, it will show you the needed vertical speed to meet your next descent constraint.Also, when you use VS and alter the vertical speed, the green arc on your ND shows where you'll be when you reach the MCP altitude - this is very useful for meeting descent constraints.

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