HI,The CI for a Boeing 737 6/7/800 must be between 10 and 30, not less not more!See in attachment, the 3 pages of the Boeing official website relatiing of this and to good understand what CI is and the difference between CI and LRC...http://www.boeing.co...ticle_05_1.htmlhttp://www.boeing.co...ticle_05_2.htmlhttp://www.boeing.co...ticle_05_3.htmlFor a correct TOD calculation, it is mandatory to use a correct CI and also to fill in (during the cockpit preparation at the departure airport) the correct winds aloft in the FMC Descent Forecast page. I sent a post here http://forum.avsim.n...cent-forecasts/ but I copy it here so that it will be easy for the TOD calculation, here it is:For those who are flying in Europe and who wants to fly very seriously here's the "Aviation Weather in Europe" link to acces to:Significant weather charts for 00 - 06 - 12 - 18 hr. UTC, Winds Aloft and Temperature Charts, Notams and so onhttp://www.flyingine...eather_maps.htmThis is freeware and update every day, here's a few pictures...Have nice flights guy'sNile Daniel

Thanks for this. But it also means FSX has to follow real weather. What do you use for that?Bert Van Bulck

Some operators use a different cost index for different phases of flight. They will climb with a low index and cruise with a higher index, for example. If later than schedule, a change in CI can help to catch up a little...You do not want to use the same CI as in the MD11... totally different aircraft with different profile... stick with values around 20-30... having a halfway valid cruise wind prediction can help a lot, as do accurate predictions of windspeed and direction on descent... Remember that the NGX, like the MD11/X, has been programmed to respond to changes in these prediction data. You want an accurate descent profile, you will need fairly accurate predictions...I use ASE for weather injection, as well as en route winds prediction. If I enter nothing into the descent forecast fields and the wind is more than minor, or there is a notable tailwind component, VNAV can be way off. Not a problem of the NGX, but of the person controlling it, or not properly...If you have a pay version of vroute, the data sheet provides a good enough estimate of cruise winds, or you can use the report generated by ASE...Andrew

Of course, just fly in FSX with option "real weather update each 15 minutes", internet connected of course!Also, chose the correct Winds Aloft chart, for exemple if your ETD (Estimated Time of Departure) is 13.30Z make use of the T+12 chart and so on...There is no need of a special weather program like ASE for exemple.For those who are flying outside Europe, it's possible to find the same weather service on the web, maybe a collegue Flight Dispatcher in the US can put a link in this thread, it would be great. I made a test flight yesterday evening arround 21.00Z from London Heathrow (EGLL) to Brussels (EBBR) STAR KOK4A with a CI of 10 and encoding correct Winds Aloft in the Descent Forecast page using T+18 Chart and the TOD calculation was adapted for a smooth and normal descent, it works perfectly...PMDG team did a great work, I wish to thanks them for this high level of simulation so much expected, it's just like the real bird but which one need correct procedures and of course to read FCOM 1 & 2 ...

HI,The CI for a Boeing 737 6/7/800 must be between 10 and 30, not less not more!Nile Daniel

It must be? I've flown many flight at CI60 and just had one at CI80.

Isn't there also some difference between the Boeing CI and MD CI methodology? I thought Boeing's were a factor of 10 less than the others. A CI of 10 on Boeing is 100 on others, whereas a CI of 680 on the MD is 68 on a Boeing. That could also be causing some confusion Trystan.

You guys keep discussing that Trystan has a too high CI but aircraft has to be able to descend even with a higher no matter what. Whats the point with a simulation if you only can use a specified amount of CI. We all know that 05-40 is the standard initial CI but if the aircraft is running late thy often increase the numbers to be there on time.

Right, but calculations and data models are only as good as the numbers you give them. Boeing programmed those calculations with a certains range of CIs in mind. Outside of that range, or closer to the extremes of that range, you're going to get errors. VNAV isn't a simple beast, and if you push it to the edge of its range, you're going to get weird results. Keep in mind that they developed a really in-depth simulation of Boeing VNAV logic to the best of their abilities within a limited FSX environment.Why is everyone railing so hard against this? Have you even tried it yet? Try a really high CI on a flight with NO weather, and go back and try it again with a lower CI and NO weather, and you're going to get some weird results on the higher CI.Trash in, trash out.

HI,The CI for a Boeing 737 6/7/800 must be between 10 and 30, not less not more!See in attachment, the 3 pages of the Boeing official website relatiing of this and to good understand what CI is and the difference between CI and LRC...

CI of 10 to 30 is not a maximum and minimum value, they are a range of typical values, so it's wrong to say "no less, no more". As Boeing say, entering 0 gives you maximum range, so you may well enter that if low on fuel, or higher values if behind schedule. The FMC should be able to cope with a higher cost index than 30 in descent and position the T/D accordingly. The problem seems to arise when there is an early height or speed restriction above the usual 250/10000' limit, as mentioned in post #5. Maybe the VNAV algorithms PMDG have developed aren't sophisticated enough for this kind of restriction.Thanks for the link though. It's interesting to see how typical CI varies with aircraft type.Kevin Hall

The thing with using a lower CI might work for flights in Europe because the distances are a lot shorter, but mind you in North America it is not uncommon for flight to Be cross country so cruising at M.75 cause of the low CI and on top of that battling +80 kts headwinds at cruise going less than 400 GS is a little annoying, with a Higher CI you might be burning a bit more fuel but at least you dont take 8 hours to fly a flight that usually lasts 6. Bottomline the TOD calculation should be able to compensate for this and increase the descent lenght, I don't have this problem with the MD-11 nor the 747, only the NGX so it might not be a higher CI but rather maybe a little variable that is out of whack in the calculation algorithm or whatever it uses to do the calculation.

I know all that and apply it when required but a plane still shouldn't nose dive at -3000 and -6000 FPM in a descent, if that were real I'd have passengers flying through the cabin

I'm probably not the first one to report this, but for some reason my TOD is always off, resulting in the plane going into 6000fpm descent or even more often VNAV kicking off with the Descent path unachievable error on the FMC.No matter what I try it constantly does this, I always set the runway and the correct altitudes for the STAR yet it constantly happens, am I missing something here? I even try starting the descent early but no luck. Is this a bug or is it something I'm forgetting here?ThanksTrystan

Several people i know had this same (or very similar) problem, a SP1 reinstall over the existing SP1 install fixed it, and we haven't experienced it since..

I think you need to do the tutorial flight to verify if this is a problem or not.A screenshot would be very helpful too.Fred.

I think you need to do the tutorial flight to verify if this is a problem or not.A screenshot would be very helpful too.Fred.

+1. I've used a CI of 90+ and even 100 on some flights and vnav works perfectly. The vertical speed on descent is faster, but that is due to the increased descent speed from the higher CI.

Yes you're right Kevin, of course I should have said "not less than 10, not more than 30 to stay in the recommended Boeing 737 6/7/800 values", sorry for the small lack of precision.With pleasure for the link, hoping this will help those wishing to fly seriously. Between passionates we are here to help each other ...Good flights to all.Nile Daniel

Yes you're right Kevin, of course I should have said "not less than 10, not more than 30 to stay in the recommended Boeing 737 6/7/800 values", sorry for the small lack of precision.With pleasure for the link, hoping this will help those wishing to fly seriously. Between passionates we are here to help each other ...EGood flights to all.Nile Daniel

Nile,It wasn't a small lack of precision though. They aren't Boeing's recommended figures. They are typical values chosen by operators. Kevin Hall