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flightsimmer747

Just curious if there a tutorial on VNAV i'm reading about but would like step / step?

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No way! The manual explains what happens more than how to do it.Here's my experience with VNAV in the NG: you program; fly; develop a VNAV issue in flight; post the question (or SEARCH) here; print; file; and repeat the process--about 27 times. Then you have a ref file and have learned a lot!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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Joe,There's information in abundance here on the forum. You could start discovering the search facility to get a grip of what's been covered over the months. If still left with issues I'm sure a lot of us would be glad to help you out.VNAV is by far the most challenging mode in the AFDS on the NG. Good luck,


Mats Johansson
PMDG Flight Test Dept
Boeing777_Banner_BetaTeam.jpg

| Asus Z270-A | Intel i5-7600K @ 4.8 GHz OC/H2O | nVidia Geforce GTX 1070 8GB OC/O2|

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Joe,First, your question is not specific. It's not even complete. I can figure out by combining the subject and the body that you are looking for a step by step of VNAV. A step by step of what in VNAV??? VNAV as I said is one of the most challenging modes of the auto flight system so you'd better have some knowledge about the basics which are there in the manual plus a lot of information here.Second, search reveals for VNAV:http://forums.avsim.net/dcboard.php?az=sho...ing_type=searchhttp://forums.avsim.net/dcboard.php?az=sho...ing_type=searchhttp://forums.avsim.net/dcboard.php?az=sho...ing_type=searchhttp://forums.avsim.net/dcboard.php?az=sho...ing_type=searchhttp://forums.avsim.net/dcboard.php?az=sho...ing_type=searchhttp://forums.avsim.net/dcboard.php?az=sho...ing_type=searchhttp://forums.avsim.net/dcboard.php?az=sho...ing_type=searchhttp://forums.avsim.net/dcboard.php?az=sho...ing_type=searchhttp://forums.avsim.net/dcboard.php?az=sho...ing_type=searchhttp://forums.avsim.net/dcboard.php?az=sho...ing_type=searchAnd this is just a tiny little part of what can be found here. A little research before asking questions never hurts. The point is. If you do your research before asking the question, you might never need to ask it.


Mats Johansson
PMDG Flight Test Dept
Boeing777_Banner_BetaTeam.jpg

| Asus Z270-A | Intel i5-7600K @ 4.8 GHz OC/H2O | nVidia Geforce GTX 1070 8GB OC/O2|

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Guest pagotan

Joe,With all due respect forums are also continuously evolving libraries and as you surely know, in all libraries you have to search for the information you need. Only if and when the information you need cannot be found or is not satisfying then it is a good move to ask for opinion. This is how a library of information evolves. Forums like this one have tens of thousand of information and although new ideas pop-up almost every day almost all possible topics have been discussed at one point in time. This is also why AVSIM provides with one of the most advanced and powerful search tool which you can access anytime from the top of the page.Michael

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Hello Joe, I agree with Mats that VNAV is most challenging but also believe that with pratice you can get a good handle on it's operation so start off small, working your way up. VNAV - It is a part of the Flight Management System that controls your veritcle profile that is contained in the FMC (Flight Management Computer). As an example, we program the FMC with all the nessary required items for a flight, we input our weights, crz altitude, a starting and ending point and at least one waypoint for an active route. Sometimes our route contains restrictions along the route say like 230/3000 YXYX on a departure. After we takeoff and at acceleration height (most likely 1000AFE but not always) and retract our flaps and speed up, most likely to 250 knots depending on any restrictions. At this point we want to engage VNAV. To be able to do this we must have a speed within a certain creteria for it to engage, so if the only restriction that is on the CLIMB page is 250/10000, we are good to go. So we engage VNAV, A/P in CMD is ON otherwise we only have F/D (Flight Director) guidence for manually following the profile. We are now climbing in VNAV, the MCP (Mode Control Panel)'s speed window BLANKS meaning the the FMS is controlling speed. VNAV works with the MCP, so say that our CRUISE ALTITUDE is set on the FMC to 32000 but our MCP altitude window is set only to 15000 in our climb, the aircraft will level off at the MCP altitude until you reset the MCP and push VNAV. Couple of notes here, on the 737 NG there are different airline options, one of these options is called VNAV ALT. If we have VNAV ALT, the aircraft will level off at 15000' but remain in VNAV with the Pilot Flight Display's (FMA) pitch annunciation showing *FMC SPD*, you simply reset the MCP and push VNAV and continue your climb. Crz is a breeze, if you desire to RAISE your crz altitude you can do it easy, simply have the CRZ PAGE displayed and reset the MCP to a higher altitude, you will see the new altitude being dynamically displayed while you are turning the dail in the CDU's scratchpad, then simply line select it into the CRZ ALT line (1 left) and up you go. You can also do this in reverse too, that is to say, you can lower your crz alt in the same manner but lower altitude (Don't raise your CRZ ALT if you are within 50NM of T/D (Top of Descent). Of course with ALT INTERVENTION you can simply reset the MCP and push the ALT INTV button to accomplish the same thing, just don't try to LOWER your crz altitude with ALT INTV or you will find yourself in a EARLY DESCENT exactly like DESCEND NOW. Descents - The FMC calculates a vertical profile at a given airspeed (it will make no attempt to follow this speed unless you get too slow) and when no unforecast winds come into play will generally keep the descent profile (speed and path). Yet VNAV PATH is going to do one thing regardless of wind, it will keep the PATH profile without regards to the target speed. So remember that the default descent mode is always PATH without SPEED. It's not really that bad because you can help it to either speedup or slow down. To slow use the speedbrakes, to add speed push F4 and hold it momentary for thrust. VNAV SPD is like VNAV PATH except that it keeps the target speed regardless of the PATH profile. All is not lost in options here either, you can keep it "close" to the path profile in the same manner you help PATH keep speed by using the speedbrakes and adding thrust. A couple things to keep in mind with either mode -Both will keep restrictions, SPD better than PATH and is why SPD is perfered over path with many restrictions down hill. Say we are in SPD and have a RESTRICTION of 250/12000 at XYXY, you ask "If SPD is not concerned with PATH how will it keep the resriction on the PATH"? It will LEVEL OFF at 12000 regardless of it's position on the PATH and and stay at 12000' UNTIL passing XYXY then resume. So in a sense it did keep at least one part of the path. VNAV PATH's speed can at times exceed the TARGET displayed, it in fact can reach VMO/MMO (Red Bricks on the speed tape RED MEANS DANGER!) so if it reaches within a few knots of this it the AFDS reverts to LVL CH. So stay ahead of your speed, if you have winds input them into the FORECASTS PAGE so that the FMC can re-calculate the descent profile. VNAV SPD's height can be a little higher than you desire, you can simply revert back to PATH on the DES PAGE or try LVL CH. APPROACH - One thing to keep in mind for APPROACH, at G/S the FMC will disconnect VNAV so be prepared. You will manually control the speed either by throttles or if it is not very windy you will set the MCP speed to VREF plus 5 (More if it is very windy). The reasons for manually controlling in windy conditions is because you as the PIC can "feel" any speed changes and REACT faster than the A/P although it is not too bad itself. Now there is a way to take VNAV to the rwy but we won't go there. This is just some general VNAV comments and forgive me if I presented anything innacurrate ;-), it's just simming ..[h4]Randy J. Smit h[/h4]


Randy J Smith

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Hi Randy thank you for taking up your time to write all this,i have been searching everywhere to try and learn Vnav, and to be quite honest your explanation was the one that really helped me. Once again thank you for putting me on the right path and helping me understand it faster :)

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Guest frankathl

Thanks for a very helpful summary of VNAV functioning, Randy!However, I must point out one MAJOR inaccuracy in your post|||||||||||v"it's JUST simming .." {my emphasis}:-):-):-)BR,Frank

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Hi I was able to perfectly play with speed and altitude at crz it was a breeze one problem i'm having is steep climb on ECON i believe, both climb phase and decent had fpm reaching 4000, would of probably gone more but i disengaged vnav to regain control. What can i be entering wrong? Is my SPD to fast making my plane want to climb in (vnav) of course.

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Could be a couple of reasons, one, could it be that you are really in CWS mode? This is Control Wheel Steering and is easy to bump or touch the controls in CMD which will revert to CWS depending on the direction your applied the pressure on the controls (Either vertical or lateral). Look at the pilot's flight display to make sure you see no yellow CWS where you normally see the VNAV modes.Two, VNAV does not take into consideration PAX comfort and the real bird is know to be quite agressive in pitching. It will at times climb or descend at such rates depending on a few things most likely WEIGHT.[h4]Randy J. Smith[/h4]


Randy J Smith

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