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PMDG 747 FMC CRZ ALT problem

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Guest lowercase

I am having trouble getting my FMC to adjust my specified CRZ ALT setting across all relevant waypoints on a flight plan.For example, I enter a CRZ ALT in the FMC of FL320, add all of my waypoints, and where my cruise altitude should now be FL320 across these waypoints, I get FL410, or FL390 or something else entirely.Is there something I am doing incorrectly? Is this a bug?No matter what order I do things in - whether I input flightplan waypoints first then input the CRZ ALT, or add CRZ ALT first - activate and then waypoints, the same result.I just want to be able to specify a certain CRZ ALT in the FMC and have it translate to my waypoints.At the moment, I am finding it incredibly frustrating to edit the flight level of every waypoint I need too - sometimes on long flights 30 or 40 fixes!If I enter into the FMC a flight level of 320, why aren't my waypoints adjusting to be set at FL320?Any help appreciated.

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Hello, try lowering your cost index. If its high, you will have a higher cruise alt. If you have a heavy fuel load the FMC shouldn't be predicting an initial crz. alt of FL410. I don't remember the FMC even stepping me to FL410. The highest I usually get is between FL380 and 390. Hope it helps. Don't forget to sign your name. Joe


Joe Colao

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Guest John Khan

Hi I don't think the Cost Index changes the Optimum Cruise Altitude,or the altitudes shown on the Legs pages of a flight.I have noticed in the 737s it shows the suggested Cruise altitude after the Cost Index is inserted in the Perf. Init. page.I always thought the Cruise Alt. went on the weight of the Aircraft.I presume you are doing things in the right order to initialise the FMC and run through the pages as per the Index. IE:- Get the weather and airport information first, Then on the FMC -Ident, Position, Route, Dep/Arr Page, select the Runway (and SID if applicable) Then go back to the Route page, select Next Page and enter the route you are have planned. (in the VIA and TO columns) Perf Init page and enter the details, Thrust Limit (to select the speed of the climb) Take Off (insert T/O flap and % if applicable)I can't think of anything that would give these strange altitudes otherwise.RegardsJohn Khan

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The LEGS page will take into account step climbs, and that is why you are seeing these level differences.If you don't want to step climb, set the step climb option to zero, and the waypoints should all indicate the same level.Can't quite remember where the step climb option is. Either on the PERF INIT page or one of the VNAV pages in the FMC.


Phil Brown

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Guest lowercase

A huge thank you to everyone who replied so quickly.It looks like the problem has well and truly been detected and fixed.As Phil suggested, it was a stray step climb setting on the second VNAV page that was fixed at FL410. Not sure if that is the default or not, as I don't recall ever using that page let alone setting options on it.For any future readers of this who may come across the same issues I did, the quick fix...Go to the 2nd VNAV page, and on the STEP SIZE option, enter the number 0 as Phil suggested (the default is ICAO). This will automatically make the vital STEP TO option (which in my case was FL410 and can't be changed without the prior step), redundant.Problem averted and thanks again for your help. The other advice has been taken on board also in regard to cost index switching and the importance of programming the FMC in the right order.Lessons learnt and some major frustrations out of the way, it is back to some flying!cheers,Brett.

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