FMC troubleshooting guide? QRH?

[DarkBlueMonkey 0]

Hi There,

I've been using the 737ngx for about two weeks and LOVE IT. But the FMC seems really hit and miss. I've got enroute charts and up to date NAVDATA off navigraph, and try to use them (with routefinder and nDAC) as much as possible, but I keep running into brick walls trying to use actual real-world routes!

 

Problem #1: I enter all the information on the pages exactly in the order described in tutorial #1, only using different waypoints. The route has no discontinuities, no DIRECT portions, it's all using valid airways. All pages have the right information, as per the tutorial (octuple checked!), but the LEGS page will not calculate Height/Speed values.

 

Problem #2: Occasionally, a speed or a height on the LEGS page will highlight purple. Whenever this happens, especially when it's the first "TO" in the LEGS page, I get all sorts of CANNOT xyz errors off the FMC, and other things tend to be purple too.

 

Problem #3: I enter a route as described by a real world plan (EGLL->EGPH), but the route created by the FMC involves a left-turn that's so tight that the A/P can't make it.

 

Problem #4: Sometimes at the TOC, before BOD, the FMC will suddenly bring up "DES NOT POSSIBLE", and sure enough, by the time I hit that left-turn on base into EGPH, I'm doing 250KTs, and even on manual with SPDBRKs, overshoot.

 

Problem #5: I enter a route as described by a real world plan (EGLL->EGPH) using current cycle navdata, but it simply will not accept a VIA/TO combination.. it always ends up with a Disco.

 

 

I realise that most of these are because i'm a noob, and I just need to spend more time googling, but my time isn't infinite.... Is there a proper FMC troubleshooting guide anywhere that would help? The tutorials are great for knowing the exact sequence of buttons to press to make the tutorial happen, but when you run into a snafu trying to do something else... it's tricky to get the information you need...

 

The information I'm looking for would be of the form of the 737's QRH:

 

 

On the XXXX page,

when YYYYY says ZZZZ, then you must ASDASDASD.

when AAAAA is <colour> this means you must QWEQWEQWE.

.

.

.

Reasons FMC might not calculate height/speed correctly on Legs:

1 - PERF INT page not complete

2 - Software Bug, restart FSX

.

.

 

FMC suddenly claims DES NOT POSSIBLE

1 - You didn't reduce MCP alt fast enough, and the margins were tight, lower it earlier.

2 - Software Bug, PMDG FMC sometimes miscalculates on tight margins, oopsie.

.

 

 

Is there such a thing? I think it'd be monumentally helpful to noobz like me.

 

Cheers,

 

Nick

[Rations 102]

Welcome to AVSIM!

 

Screen shots, particularly of the various pages in your FMC and of your ND, would be immensely helpful.

 

(with routefinder and nDAC) as much as possible, but I keep running into brick walls trying to use actual real-world routes!

RouteFinder is an automated route generator, so some of its routes may not be completely realistic. FlightAware and the Real-World Flight Plan Database feature real-world routes.

 

Problem #1: I enter all the information on the pages exactly in the order described in tutorial #1, only using different waypoints. The route has no discontinuities, no DIRECT portions, it's all using valid airways. All pages have the right information, as per the tutorial (octuple checked!), but the LEGS page will not calculate Height/Speed values.

 

Problem #2: Occasionally, a speed or a height on the LEGS page will highlight purple. Whenever this happens, especially when it's the first "TO" in the LEGS page, I get all sorts of CANNOT xyz errors off the FMC, and other things tend to be purple too.

 

Problem #3: I enter a route as described by a real world plan (EGLL->EGPH), but the route created by the FMC involves a left-turn that's so tight that the A/P can't make it.

 

Problem #4: Sometimes at the TOC, before BOD, the FMC will suddenly bring up "DES NOT POSSIBLE", and sure enough, by the time I hit that left-turn on base into EGPH, I'm doing 250KTs, and even on manual with SPDBRKs, overshoot.

How are you loading fuel and payload? What was the weight of the aircraft in each of these situations?

 

I just need to spend more time googling, but my time isn't infinite.... Is there a proper FMC troubleshooting guide anywhere that would help? The tutorials are great for knowing the exact sequence of buttons to press to make the tutorial happen, but when you run into a snafu trying to do something else... it's tricky to get the information you need...

The second volume of the B737 FCOM contains useful information about the intricacies of the FMC. While it is best to develop a basic understanding of the FMC before operation (instead of diving in and continuously troubleshooting the issues you run into), I understand that you may have time limitations. Look for the FCOM section regarding FMC messages.

[VIPERGTSR01 22]

Problem #1: I enter all the information on the pages exactly in the order described in tutorial #1, only using different waypoints. The route has no discontinuities, no DIRECT portions, it's all using valid airways. All pages have the right information, as per the tutorial (octuple checked!), but the LEGS page will not calculate Height/Speed values.

 

Is your IRS configured and aligned properly? Do you have the ZFW, CI etc prompts (PERF page) filled out first?

 

Problem #2: Occasionally, a speed or a height on the LEGS page will highlight purple. Whenever this happens, especially when it's the first "TO" in the LEGS page, I get all sorts of CANNOT xyz errors off the FMC, and other things tend to be purple too.

 

 

When they're in magenta it means they're restictions placed by the procedure, you can delete them. If these restrictions are beyond the calculated capability of the aircraft (going by your weight input, CI etc into the FMC) you will get warnings like this. Or if the restriction requires a climb during the descent or something weird you will get messages.

 

 

Problem #3: I enter a route as described by a real world plan (EGLL->EGPH), but the route created by the FMC involves a left-turn that's so tight that the A/P can't make it.

 

 

Usually from excessive speed, charts usually give you max speeds to take tight turns if it is part of a airport procedure (sid, star etc). Slow down prior or place the speed restriction in the FMS legs page.

 

 

Problem #4: Sometimes at the TOC, before BOD, the FMC will suddenly bring up "DES NOT POSSIBLE", and sure enough, by the time I hit that left-turn on base into EGPH, I'm doing 250KTs, and even on manual with SPDBRKs, overshoot.

 

 

Once again the FMS calculated the descent with given restrictions is too steep, your cost index (CI) might be very high, try lowering it (15-30 is normal for airlines). I sometimes get the message but can manage it, think ahead. At higher alts it can be helpful to increase speed which increases drag and descent which allows you to get below the VNAV PTH. Also use speed brakes earlier if you need to ensure your stay on path and even hold off descent to lower speed, bring out flaps and even gear if you have to earlier than usual and this will add a ton of drag to get you back on path. Just takes practice but most of the time you shouldn't have too much trouble.

 

Problem #5: I enter a route as described by a real world plan (EGLL->EGPH) using current cycle navdata, but it simply will not accept a VIA/TO combination.. it always ends up with a Disco.

 

Disconnects are normal, if the end of the last waypoint is not the same as the next waypoint you will get a disconnect, you can close them up and check the plan to make sure it look correct but don't worry about them.

 

 

As mentioned pictures do help a lot, sometimes it makes all the difference.

[DarkBlueMonkey 0]

Hi There!

To Both of you, thanks for the response. THE FCOM does give a lot of help with what the messages ARE, but the problem I have is that sometimes something pops up which shouldn't... or doesn't pop up which should.

 

I enter all the details EXACTLY the same as the tutorial, except that instead of flying to EHAM, I fly a slightly shorter route to EGNT or EGPH. All PAX/Fuel/Payload values the same.. sometimes I just hit 'random' and make sure the payload isn't too high.

 

 

For example, in the tutorial, it goes through the process of removing the speed/height restrictions at SUGOL, etc.. and then after sorting the INIT REF page, the LEGS page fills with height/speed information. Sometimes, this just doesn't happen, and I wish I knew why. Is it because I activate the route at the wrong moment? Did I drop a dorito and wege the CLR key?!!

 

All I know is that if I quit FSX, reload it, restart the flight, and follow (what I THINK) are the exact same steps, I stand a 50/50 chance of it working. but I just don't know if it's a PIBCAK, or an FMC 'feature'. :(

 

I've taken a picture of each step as I proceed through setting up the FMC for my flight, you can find it at (Just to annoy me, it worked this time) :-

:

 

FMC_worked.jpg

 

 

However, I quit FSX, restarted and followed the exact same procedure, on the second (and third time before PDMG_737NGX.DLL crashed), I got this:-

 

FMC_failed.jpg

 

 

I'm still a total noob at this, but I suspect that there's a bug somewhere that if you do something sliiiightly out of order, it snafus the FMC irretrievably, and only a complete quit/restart will sort it. Trying to restore it by trial and error ends up with a CTD. The PMDG DLL seems very brittle to me (as a developer), but that's just my 2c.

 

 

What I really would like is a QRH for the FMC, that goes into troubleshooting, rather than explaining what all the buttons do. Does that make sense? I'll go back over FCOM 2 with a fine toothed comb, and see if my answers are hidden in there.

 

 

Thanks for the recommendation of flightaware and checking the weights etc. I'll make triple sure I'm within specs from now on.

 

 

Nick

[rsvit 16]

When they're in magenta it means they're restictions placed by the procedure, you can delete them.

 

No, it means next resriction you'll met on your route.

 

FMC_worked.jpg

 

Speed on waypoints after runway waypoint RW07 are missed approach waypoints, so speed is not calculated for them.

 

FMC_failed.jpg

 

The only strange thind I see here is your CG. Try to check out payload again.

 

BTW did you executed perf init changes? For some reason on legs page altitude constraints are shown in FL below the transition altitude. Who knows, but maybe it's a bug and you'd better write a support ticket.

[DarkBlueMonkey 0]

Hi There,

to produce both of those flows I used my own checklist, so apart from the fact that I was sat on the rwy, so used a different amount of fuel while running the APU, they both had identical values for PAX/Payload/Fuel and I used the same process.

 

The only thing I cannot guarantee is that I didn't skip to the wrong page, before going back and hitting EXEC. For example, I may have thought "OK, next I go to RTE..." clicked RTE, and then thought "whoops.. didn't activate those changes", then go back to PERF INT, and click EXEC.

 

i'll try again tonight and see how I get on. I just started up FSX, and despite buying brand new AIRAC data three days ago, the FMC is already saying "NAV DATA OUT OF DATE", but it's showing the right Code JAN10FEB10/2013 (or something like that). *sigh*..

 

This is why I'd like a clearer QRH for the FMC.. It's so hard to know if this is all my noobness, or there's an actual bug (even if the FMC simulates a real bug in the original unit).

 

 

N.

[DarkBlueMonkey 0]

I'm trying to troubleshoot this myself... But does anyone know if that when you change your fuel loadout, you have to update the FMC manually? Here's a little experiment I just did:-

 

 

 

When I say "the other information", I mean the V-speeds, alts, etc on the RTE page... This doesn't happen every time, but occasionally when it does, another symptom is that it won't accept a value into the Cost Index field, any value entered is ignored...Another (happening right now) is that the ND does this:-

 

 

A restart of FSX will often clear it. Any idea what I'm doing wrong? Or does everyone else just shrug and restart FSX when this happens? a restart only takes 30 seconds, so if a flight takes an hour, an extra 30s to restart fsx is acceptable, I guess..

 

N.

[Oliver Branaschky 2]

If you change the fuel load, you will have to update the ZFW on the PERF INIT page. Simply click on the LSK next to it twice. Don't forget to EXECute the modification!

 

What's wrong with the ND?

 

 

Oliver Branaschky

[DarkBlueMonkey 0]

Hi There,

Thanks for replying.. Yeah.. There's a couple of places you have to make sure you double-click to get it to 'stick', and I always give the ZFW a good poking whenever I pass that page

 

I'm sure it's something I'm doing wrong.. but the ZFW isn't the thing that's wrong.. I've not modified the PAX/PYLD, I've modified the fuel loadout, so ZFW doesn't change..

 

The ND's displayed route is flipflopping between two projected courses. One "hits" the WPT, one misses it.. it's flipping each time the ND updates (I've set it to 10fps for perf reasons, so it flips every 100ms).

 

Ach, It's gotta be PIBCAK if nobody else sees this issue... If I work out what I'm doing wrong, I'll update

 

Thanks for all your help (everyone)! It's much appreciated!

 

N.

[Rations 102]

Trying to restore it by trial and error ends up with a CTD. The PMDG DLL seems very brittle to me (as a developer), but that's just my 2c.

Have you tried applying stability tweaks?

 

Two essential stability tweaks many people recommend are:

HIGHMEMFIX=1 in FSX.cfg, which largely eliminates aircraft graphics rendering (“skeleton”) issues.

UIAutomationCore.dll in the FSX main folder, which largely eliminates memory insufficiency/usage errors (e.g., after long periods of flight, using menus too frequently, etc.).

For specific instructions, please reference the appropriate sections of Word Not Allowed's Guide (use Find in your browser).

 

I have found that loading fuel to PMDG aircraft must be done very carefully. Never use default fuel and payload loading tools.

 

First, I determine the amount of fuel required for flight. Then, I load the PMDG aircraft (the aircraft for the FSX default flight should always be a non-complex one) and commence the flight. After the flight has loaded, I immediately pause the simulator and select the cold-and-dark cockpit state, so the aircraft does not automatically configure itself to a taxi state. I then un-pause the simulator and load fuel via the PMDG fuel menu, ensuring that I hear clicks. Sometimes fuel will not load properly. I can tell if the fuel pumps have not been automatically configured or if the EICAS fuel page displays incorrect values. For example, sometimes I will request 42000 lb, only to have the fuel load remain at the default of approximately 104000 lb. When such errors occur, I restart the simulator, as I have found that reloading fuel may cause various issues such as a lack of wing flex.

 

So, to answer your question, I would recommend restarting the simulator if you find that you are experiencing fuel loading issues. For me at least, making an effort to continue is not worth it due to the possibility of various simulator errors that only lessen the immersion and realism factor.

 

The ND's displayed route is flipflopping between two projected courses. One "hits" the WPT, one misses it..

I have experienced this, too. I am guessing that it involves the buggy winds of FSX, which can be remedied by wind smoothing functions of programs such as FSUIPC. What weather add-ons are you using, if any, and what winds are you experiencing when your issue occurs?

Edited January 22, 2013 by zowen11

[Oliver Branaschky 2]

You're right, of course, about the ZFW. I should have been more clear: pressing the LSK next to the ZFW will update all weights, i. e. GW. What I only now realize, though, is the fact that the fuel didn't update. I've never seen that before.

 

As far the ND is concerned: does the problem still persist after entering the V-speeds?

 

 

Oliver Branaschky

[Lek767 37]

I'm trying to troubleshoot this myself... But does anyone know if that when you change your fuel loadout, you have to update the FMC manually? Here's a little experiment I just did:-

 

 

Hi there!

 

I'm trying to replicate the erroneous results you're getting, but can't seem to make the FMC misbehave the way it does for you. I *can* tell you how it *should* be working: on the FUEL configuration page, the moment you select a different fuel load (such as 2/3, as shown in your bottom left screenshot), the GW and CG parameters should be updated automatically and immediately show the correct values pertaining to the amount of fuel on board. That is, with a 2/3 fuel load (and a payload set to zero, per your example), you should get the following values:

 

GW = 121.7 (x 1000 lbs)

MTW = 174.7

ZFW = 91.3

CG = 21.7%

 

Your screenshot clearly shows that these parameters do not get updated, as it still displays the previous values appropriate for a 1/3 fuel load. There's definitely something fishy going on here.

 

Contributing to the confusion could be that you seem to enter the amount of fuel on board manually on the PERF INIT 2L LSK. Strictly speaking, you don't have to do that -- but if you do, you'll have to take care to update the GW value manually as well. If you leave the "PLAN" value on the 2L line blank (i.e. ---.-/30.6, for example), the FMC will calculate and update the GW automatically, based on the ZFW and the actual amount of fuel on board. That said, I don't think this could be the root cause of the problems you're having but it is something you should take into account.

 

Incidentally, could you describe how exactly you launch FSX, select the NGX and load your flight? There are some pitfalls to be avoided here, and depending on how you load the aircraft, strange behaviour (such as the FMC/fuel config shenanigans you're encountering) could ensue.

 

Good luck!

[DarkBlueMonkey 0]

Hi All!

Wow, thank you all so much for assisting with this! I absolutely love this plane, and with the FS2Crew voice addon, it's really superb!

 

I've tried the routine by zowen above three times, and it works perfectly every time, so that's going to become my procedure... I don't know if that's the cure, but 100% success definitely floats my boat...

 

As for the stability tweaks: Yes and no. I've done the two essential ones, but when I use the PDMG-recommended fsx.cfg tweaker tool online, the DLL tends to crash MUCH more frequently. At worst, I cannot start a free flight with the 737, I have to start it with the trike, then switch planes to the 737 (the trike is my default plane on the start menu, and in my default flight). It seems to be the optimisations to do with memory usage and allocation.. So I've left them at stock values. I get 40fps in and around EGLL using the VC, so it's all good. That's why I think the DLL is a little brittle.. It doesn't bow out gracefully, it just takes a shotgun to FSX and pulls the trigger ;-)

 

No, I have no Weather FX installed and the in-game Weather is off.. clear sky for this guy... ;-) I followed the setup to the letter. I have no weather addons either (although I'm sorely tempted by the nice gfx of some of them).

 

I have done a lot more playing, and the problem seems to occur when I'm double-checking my route using vroute or nDAC. Something about switching in and out of FSX in windowed mode seems to really irritate the FMC. I wrote the route down on a notepad, and entered it without leaving FSX, and I haven't made it crash yet (although the flopflopping ND still happens).

 

To Lek: Thanks for the figures, I'll use those to check my loadouts from now on. I've been using the figures from FCOM1 to guesstimate the right numbers, but it's nice to have actual rw values. OK, here's my loading procedure:

 

1. Double-click on FSX.EXE

2. Wait for the spinny trike

3. Choose the 737ngx (BA livery, cos I like it).

4. Choose EGLL, any heavy gate.

5. Click "fly"

6. If FSX crashes, wait 10 seconds, then go to step 1.

7. Load Panel State Cold-And-Dark

8. go.

 

I've got everything set according to the manual, don't try to load a 737 after a different 737 of the same config, don't scratch my nose while blinking.... all the things they suggest in the manual.

 

 

 

I'm going to play with it some more, but I think Zowen's workaround works for me.

 

 

 

N.

[Rations 102]

I've tried the routine by zowen above three times, and it works perfectly every time, so that's going to become my procedure... I don't know if that's the cure, but 100% success definitely floats my boat...

That's good to hear, but even I occasionally experience issues, so no loading method is perfect. I don't know whether it is true or not, but I initially found that failure to un-pause the simulator before loading fuel resulted in fuel loading errors, so ensure that you un-pause FSX before loading fuel every flight.

 

I've done the two essential ones, but when I use the PDMG-recommended fsx.cfg tweaker tool online, the DLL tends to crash MUCH more frequently.

For many people, it seems as if a reliable version of UIAutomationCore.dll cures many memory insufficiency crashes, but I have heard of cases in which it only made things worse. Be aware that there are also manual tweaking guides available, notably Word Not Allowed's Guide and NickN's Guide. While many of the tweaks suggested by the three tweaking approaches are similar, it's worth reading and trying each of them, due to the nature of the unpredictability of FSX and its vastly differing behaviors on different computer systems.

[DarkBlueMonkey 0]

Zowen, you are a FREAKIN' GENIUS.

 

I just realised that when I alt-tab out to nDAC to get my route, or check the enroute chart, and then alt-tab back, FSX is "paused", even though the FMC window is still operational.. Whenever I use it to plot the route, then enter the fuel load, it produces exactly those symptoms! It looks like you're able to do about 50% of your work with FSX paused, but some of the FMC's internal calculations must be tied to the main engine loop! Sometimes if you set it up paused, and then unpause it, the FMC start spitting out errors about MACH's and SPEEDs. If programming the FMC when FSX is paused is not a supported operation, then the FMC should be paused when FSX is paused too..

 

That's why it didn't bork when I didn't alt-tab out! I *knew* it was a PIBCAK issue. I've been beating my head against the yoke for days over this before baring my incompetence in a public forum ;-)

 

I've tried a lot of tweak guides and tools for FSX, but they all just end up with FSX being slower, or PDMG737NGX.DLL crashing FSX.

 

Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you! Thank you!

 

If there were virtual cookies to hand out, I'd hand one over right now!

 

N