VNAV ISSUE - TUTURIAL 4

[Davidb777 0]

Hi there. I've been doing the tutorials for the 747-400X, and have reached tutorial 4 (Lesson 4, Part 2) - I'm having what I think is a problem or erratic behavior of the VNAV function while climbing. As a refresher, this lesson is to takeoff using the autopilot and autothrottle, reach several mid level altitudes (3000, 6000, and 18000), before reaching a cruise of FL210. First things first, before doing the tutorials, I read the PDF manuals that came with the DVD I purchased. I've had this plane for about a month. I have also searched this forum for the problem that I'm having, found a couple of entries relating to it, tried several of the methods found, but I'm still getting the issue.Now, onto the problem. The flight is a preloaded flight found in the tutorials I downloaded. I preload Lesson 4, Part 2, and the plane is already lined up with VNAV armed, ready to go. The altitude in the MCP is initially at 3000, but as instructed in one section of the lesson, I change it to 6000. There are two altitude restrictions in the FMC, both set at 3000 for two made up fixes - one at 5 miles from the airport, and the other at 15 miles. The lesson teaches the reader how VNAV works. What's supposed to happen is that VNAV will take me up to 3000 under VNAV SPD, reach 3000 (the first altitude restriction in the FMC) with VNAV PTH, and upon terminating the 3000 altitude restriction, VNAV SPD engages again to take me up to 6000 (which is set at the MCP), at which point VNAV ALT should engage. Then onto 18000 again with VNAV SPD, and finally reach FL210.When departing 3000 to 6000 (and ending the alt restriction), VNAV automatically pitches the plane up and changes correctly to VNAV SPD, but when reaching about 4000, the VNAV light disengages and the SPD and ALT modes are seen engage on the display (PFD.) The plane levels at 6000 and the ALT HOLD light turns on. VNAV is still "off", i.e., VNAV ALT is not engaged, as is depicted and explained in the instructions of the tutorial of what should happen. When leaving 6000 up to 18000 (changed in the ALT MCP), I press on the ALT MCP button, and hit VNAV, but nothing happens. I tried using the VS to 1000, and then hitting VNAV twice, but nothing happens (this was explained in a posting I read.) I used FL CH, which works perfectly, and then tried to change to VNAV while clicking it twice (sometimes more), but it doesn't change modes. It always stays at FL CH.The curious thing is that when reaching 10,000, the transition altitude, the airplane accelerates to the FMC speed of 323, but the mode is still at FL CH, not at VNAV. I was able to sometimes re-engage VNAV after passing this altitude of 10000 (after clicking VNAV several times), but it was not consistent. At 1000 feet from 18000, instead of VNAV changing to VNAV ALT, it again disengages, and the SPD and ALT modes are engaged. From 18000 to FL210 (after pressing the ALT HOLD button), I need to always use FL CH to initiate the climb, then I press VNAV and it finally engages and works as expected. It seems that at the initial alt restriction, VNAV operates as expected, and also works fine on the last altitude leg to FL210, but the intermediate levels is where the VNAV function acts differently (compared to how it's explained in the tutorial.)I have flown the specific scenario about 10 times, and I can repeat what I have explained above. In reading the tutorial, it doesn't mention anything about the SPD and ALT modes, and from what I understand, I should get a VNAV ALT when reaching the intermediate altitude holds. In other words, it should always use one of the VNAV modes, either PTH, SPD, or ALT. Maybe I'm going about this the wrong way or not understanding how VNAV really works, and sure would appreciate any feedback on this matter to manage the VNAV function correctly. I know the post was long, but needed to be specific. Here are my computer specs:FSX SP2, Windows XP Home SP3 32 bit, 4 gigs Ram, Geforce 9800 GTX+ 512 MB, several airplane addons, payware FSUIPC, ASX + XGraphics, GEX, RC4FSX is on its own dedicated hard-drive.Thank you,David Bolanos

[Flamin_Squirrel 71]

Things to double check: Make sure you've set the cruise atl correctly in the perf init page of the FMC.Confirm you've cleared alt restrictions by checking the VNAV page on the FMC.

[Davidb777 0]

Thank you for trying to help me with this.

Make sure you've set the cruise atl correctly in the perf init page of the FMC.

Confirmed, it's set at FL210.

Confirm you've cleared alt restrictions by checking the VNAV page on the FMC.

Confirmed - when I press the ALT Selector Knob, the altitude restriction on the legs page and VNAV page of the FMC is cleared.I tried this flight again confirming the above, and same thing happens. I get no VNAV ALT mode at intermediate set altitudes. I did find the following:

1. I'm established initially at 3000 (first altitude restriction) under VNAV PTH (correct), and upon passing it, VNAV SPD engages and takes me up to the new MCP ALT of 6000 (altitude restrictions have been cleared both on legs and VNAV pages on FMC.) Again, at 4000 feet, VNAV disengages, and SPD and ALT modes engage all the way up to 6000. So I have in the Autopilot Mode Anunciation in the PFD, modes: SPD, LNAV, and ALT, and the alt HOLD is lit.
2. Once level at 6000, and going up to say 15,000, at least I've found a way to engage VNAV, as I was not successful before, until sometimes passing 10,000. I still can't get it to work by setting the new altitude in the MCP alt window, pressing the alt selector button, and clicking on VNAV. But, if I enter an arbitrary number below 15000 and higher than 6000, hit the ALT Selector Knob, use FL CH, and commence the pitch, and then change the altitude to its correct altitude of 15000, pressing the alt selector knob, and then pressing VNAV, it engages! Tried this several times at different mid level altitudes (below and above 10000), and it always worked.

So, at this moment, I can't get VNAV to correctly display a VNAV ALT mode when holding at intermediate altitudes set in the MCP altitude window. I tried another flight, from KPHX to KLAX (also part of the tutorial), FL340, confirming the FMC (VNAV and perf pages) was properly setup, and that has an initial altitude "hold" at 7000 per the departure procedure, and same thing happens just before reaching 7000. VNAV disengages, and SPD and ALT modes engage. I then need to use FL CH, and do the short work around to engage back again VNAV to take me to FL340. In the end, I've found a way around it and if that's the way I need to fly this bird, then I'll live with it, but I'm still trying to figure out if this is: 1) a bug, or 2) something I still don't understand about the way VNAV specifically behaves on this plane, or 3) just something that is haywire on my install of the 747.Thanks.David Bolanos

[Flamin_Squirrel 71]

While climbing under VNAV you should have THR REF | LNAV | VNAV SPD. Are you getting that at any point?

[Davidb777 0]

Yes. An example of the modes I get - a flight to FL340 with a "hold" initial altitude of 5000 set on the MCP alt window (not a hard altitude restriction, so no restrictions set on the FMC):

1. just after takeoff, when LNAV and VNAV go active= THR REF | LNAV | VNAV SPD
2. at about 1000 feet to go before reaching 5000, modes change to = SPD | LNAV | ALT (this doesn't look right, I should get VNAV ALT based on the tutorial)
3. to go to say 18,000 given by ATC (as an example), I use FL CH (hitting the alt selector button and then VNAV will not work in my case as previously explained) and set 12,000 (arbitrary) on the alt window - plane changes to = THR | LNAV | FLCH SPD
4. then I set 18000 on the alt window, hit on the alt selector button, then press VNAV, and voila, modes change to = THR REF | LNAV | VNAV SPD
5. Because VNAV disengages before reaching 5000, and because I get modes SPD | LNAV | ALT at 5000, hitting on the alt selector knob and then VNAV will not activate VNAV (it's not engaged to begin with.) I should never have lost the VNAV mode; holding at 5000, I should get VNAV ALT and then I would be able to execute the selector knob to continue climbing under THR REF | LNAV | VNAV SPD
6. When reaching FL340, VNAV changes to THR REF | LNAV | VNAV PTH, which is the correct mode

What is not working is that I don't get a THR REF | LNAV | VNAV ALT at 5000 or any other hold altitudes I set in the alt window, as it's explained in the tutorials. Something is quirky with the VNAV function, in my opinion, at least with these tutorial files. If it's not too much to ask, can you or someone else try this tutorial (Lesson 4, Part 1 or 2) and see if you get the VNAV ALT modes at any point during the intermediate holds? It'll take 5 minutes at most, if you have the files ready to go. What I'll do as well is a totally different flight, made from scratch using FSX flight planner, and see if the modes behave the same (or different) and report back. If they act the same as I've been experiencing, then I'll know that the tutorial files that I copied are not the culprit.Thank you for your continuing support to get to the bottom of this.David Bolanos

[Davidb777 0]

The problem is the "old" files of the tutorial, which were written for FS2004, but work for FSX. Somehow, the VNAV function acts quirky with FSX (at least in my setup.) I did a flight created from scratch (up to FL250 only) from KMIA to KDFW, and VNAV works perfect. I get all the modes working flawlessly, so no need for anyone to try the tutorials as I asked in my previous post - thanks if you did anyway. In case anyone out there is doing the tutorials by step like I did and using FSX, this might help you if you encounter any issues like mine.ThanksDavid

[Guest FruitSalad]

Thank you I managed to get to Lesson 4 part 4 before noticing this because I manually set up Lesson 4 part 2, subsequently downloaded the lessons and for the hell of it tried them to see if they worked in FSX. Annoyingly they work perfectly until exactly as you describe above. I got stuck at 7000' in hold mode and couldn't get out for love nor money. The reason I downloaded the lessons was because I didn't have the route programmed in and couldn't seem to replicate it using "Routefinder".I'm going to try manually setting up the lesson but loading the company route in order to continue with the flight as planned, I'll report back. Thank-you for posting this I've spent about an hour looking for this problem and your the first person I've seen to post it, how did you find out it was an FSX issue?EDIT: It doesn't work, the company route is a .rte whereas the new company routes are .rt2 the only option is to copy the route out of the FMC onto paper and input it and save it as a new company route

[Davidb777 0]

Glad it worked for you. I found out by finally trying to eliminate the variables I thought were creating the problem, since I had spent so many hours trying to find out in the Internet if anyone had similar issues, but to no avail. Since these files were created for FS2004, but are reported to work for FSX (you can find many posts relating to this, and they do "work"), my first trial was to eliminate the possibility that some part of the original code for FS2004 was not transferring well in Lesson 4 to FSX. I've read so much about the VNAV function, that I knew something was not right in my tutorial flight - it's supposed to do things in a certain way. So, decided to fly an original flight from scratch, and doing everything myself instead of using the tutorial files. Gladly, that did it! I imagine the first lessons, because they are "easy" in terms of what you are doing (and not using the autopilot), work perfectly, but as you progress into Lesson 4 and VNAV, which is a mathematical intensive application, something does not write well into FSX, hence the faulty VNAV.David

[Guest pcpilot2010]

Hello !I have been AGONIZING with exactly the same problem, going methodically through the tutorials (which are of course an absolute joy to follow) - but got stuck in Chapter 4, the MCP intervention part (to follow ATC commands) won't work as it is supposed to; i.e., instead of going to the VNAV ALT mode one ends up in the plain ALT mode (Hold) and there is no way of recovering back to VNAV. Many many thanks for your advice (I am yet try it out and build from scratch though, but hopefully my situation should be similar) - it was smart of you to nail this down to an FS2004-FSX compatibility issue; I never thought of that.Ravi

Glad it worked for you. I found out by finally trying to eliminate the variables I thought were creating the problem, since I had spent so many hours trying to find out in the Internet if anyone had similar issues, but to no avail. Since these files were created for FS2004, but are reported to work for FSX (you can find many posts relating to this, and they do "work"), my first trial was to eliminate the possibility that some part of the original code for FS2004 was not transferring well in Lesson 4 to FSX. I've read so much about the VNAV function, that I knew something was not right in my tutorial flight - it's supposed to do things in a certain way. So, decided to fly an original flight from scratch, and doing everything myself instead of using the tutorial files. Gladly, that did it! I imagine the first lessons, because they are "easy" in terms of what you are doing (and not using the autopilot), work perfectly, but as you progress into Lesson 4 and VNAV, which is a mathematical intensive application, something does not write well into FSX, hence the faulty VNAV.David

[Ioan92 63]

Hey guys, I'm having the same kind of problem!My VNAV turns off and sends the CHECK TGT ALT message in my FMC. It then gets stuck on ALT HLD then.I'm confused about how the MCP ALT knob works as I'm having trouble understanding the manual's part on this. I've built a small route from scratch: EDDF>DKB>XERUM>BURAM>EDDM or about 168 NM.

[Guest pcpilot2010]

Basically, VNAV means that the Flight Director cues follow exactly the altitude profile shown on the LEGS page of the FMC. In addition, if you activate the autopilot, then the servos will automatically ensure that the plane follows the cues by itself. Now, in the VNAV autopilot mode, when the plane climbs the top right of your PFD should show VNAV SPD (the meaning of which is explained in chapter 4) and when you are level it will show VNAV PTH... HOWEVER, this profile is intercepted by whatever number you have programmed into the MCP ALT window, if that number happens to be smaller than the current altitude per the FMC (on a climb, that is - it is the other way round for descends). So, as you are climbing towards the next level per the FMC in VNAV SPD mode, if you encounter an MCP ALT intermediate number, you would stop and hold there, till you clear that restriction... The difference from a standard ALT hold (in the absence of VNAV) is that this is a tentative situation, and the moment you pull this number to a figure higher than the next VNAV level (I think you may also have to push the knob to release VNAV ALT) the original FMC objectives take over, so you get back to VNAV SPD followed by VNAV PTH once you reach the next level, etc (all happening per the thrust/speed profiles decided by the FMC)... The problem we encounter (with the prepackaged lessons) though is that if you try to intervene with an MCP ALT setting, then the control mode switches to plain ALT (rather than VNAV ALT). Beyond that if you want to climb, etc., you have to do it by one of the non-FMC modes such as FLCH (and you may specify a climb rate manually etc.) - in short one doesn't know how to relinquish control back to the FMC. Well, as David Bolanos (Davidb777) discovered, this is because you are inadvertently force fitting the old FS2004 saved examples packaged with the lessons on FSX - they are not compatible. So, if instead of using their model, you build an exact replica in FSX from scratch you wont have this problem, and you will observe a behavior exactly as described in Chapter IV. Incidentally, I too verified this, building from scratch, and it now works perfectly for me as well !!!! Good luck !

Hey guys, I'm having the same kind of problem!My VNAV turns off and sends the CHECK TGT ALT message in my FMC. It then gets stuck on ALT HLD then.I'm confused about how the MCP ALT knob works as I'm having trouble understanding the manual's part on this. I've built a small route from scratch: EDDF>DKB>XERUM>BURAM>EDDM or about 168 NM.

[787flyer 633]

Guys,Sorry to rehash this but this has been bugging me. I'm still having problems with this.I tried building my own flight plan (given the tutorial seems to be designed for FS2004) but I still only get the MCP ALT intervention and not VNAV ALT. In my case, no Alt restrictions programmed into FMC, CRZ altitude set to a high level but just setting MCP to some intermediate value.Can someone provide the specific steps to get into VNAV ALT mode?Incidentally, I notice there's an Option in the PMDG Add-ons drop down menu and if you look in Options/AFDS, there is a check box for "VNAV ALT (if applicable)". On my set up the check box is checked but the option is grayed out.Just wondering if this has anything to do with it?Would appreciate some guidance with this.Cheers,

[downscc 1,327]

The only step I ever recall is setting the cruise altitude and step interval (usually 0 unless it is a long flight then I use 2000). Review the LEGs pages, and the waypoints/fixes will have a climb segment, cruise and arrival. There is usually at least one constraint introduced by the STAR and of course the approach FAF. Don't you see this during preflight?Above 400 agl, AP on and VNAV on and the rest is automatic until descent. I don't understand your question, how do not get into VNAV ALT?

[787flyer 633]

Hi Dan,OK. I have THR REF/LNAV/VNAV on the ND, have taken off and have 9000ft set in MCP and accelerate to 250kts, flaps clean configuration.In the FMC I have Step Size set to 0 and CRZ ALT set to 350. I have removed all Alt restrictions from the SID on the climb phase but with the STAR loaded I have some Alt restrictions in the plan.When I level off at 9000, VNAV switches to ALT mode, so no VNAV ALT. The only way I can re-enage VNAV is via FL CH and then to VNAV.On the descent into EDDS while I was flying earlier, I did notice VNAV ALT activate since MCP was set higher than the Alt restrictions, so VNAV ALT is operational in descent. I just can't get it to activate during the climb phase. I'm sure I'm missing something!thanks,

[downscc 1,327]

You change to ALT at 9000 logically because of the MCP constraint. When cleared higher, change MCP to next clearance limit or cruise (350), then press the ALT button. The value will be put into the FMS and you should be back to the VNAV mode. See page 8-15 in the AUTOMATIC FLIGHT MANAGEMENT SYSTEMS manual.The manual is required reading :)