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Precision Simulator update 10.132 (14 February 2021) is now available.
Aerowinx NG FMC and More is now released.

Author Topic: NG FMC calculations  (Read 496 times)

Ton van Bochove

  • Join date: Jun 2009
  • Location: EHAM/EHBK
  • Posts: 355
NG FMC calculations
« on: Fri, 22 Jan 2021 22:00 »


It happens on a regularly basis that the calculation of the cruise altitude is not realistic ( e.g. 4000 feet) No problem just rejecting and choose the right altitude yourself. The last two flights strange calculations like this appear. What might cause this? I have no situ.
Ton

Hardy Heinlin

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  • Join date: May 2009
  • Posts: 12310
    • Aerowinx
Re: NG FMC calculations
« Reply #1 on: Fri, 22 Jan 2021 22:15 »
Very short route, very early altitude constraint near destination, or no destination entered, or destination very close but no destination altitude constraint entered etc. pp.

Ton van Bochove

  • Join date: Jun 2009
  • Location: EHAM/EHBK
  • Posts: 355
Re: NG FMC calculations
« Reply #2 on: Fri, 22 Jan 2021 22:18 »
Lot of choice Hardy ;-) Next time I safe the situ.
Ton

Hardy Heinlin

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  • Join date: May 2009
  • Posts: 12310
    • Aerowinx
Re: NG FMC calculations
« Reply #3 on: Thu, 4 Mar 2021 12:09 »
Hi Ton,

I just recevied your mail with further screenshots.

Please just save a situ file and post it here. Screenshots don't help me to analyse your situation.

A situation file contains thousands of variables. Only that can help me to give you an answer.


Best wishes,

|-|ardy

Hardy Heinlin

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  • Join date: May 2009
  • Posts: 12310
    • Aerowinx
Re: NG FMC calculations
« Reply #4 on: Thu, 4 Mar 2021 12:41 »
Just found some situ files attached after the screenshots.

But I see no problem. They all show a correct CRZ ALT profile on the LEGS.

Do you see incorrect values on your hardware CDU only, and correct values on the PSX server's computer monitor?

If so, maybe your PSX client for your FDS CDU screen is out of sync?


|-|ardy


P.S.: Maybe there are some misunderstandings. The FMC doesn't calculate your initial CRZ ALT. If you see a CRZ ALT of FL210 on the CRZ page in 1L, then you have entered this value yourself, or you loaded a company route that contains a CRZ ALT. In either case: That value doesn't come from the FMS computer.

Ton van Bochove

  • Join date: Jun 2009
  • Location: EHAM/EHBK
  • Posts: 355
Re: NG FMC calculations
« Reply #5 on: Thu, 4 Mar 2021 15:29 »
Just found some situ files attached after the screenshots.

But I see no problem. They all show a correct CRZ ALT profile on the LEGS.

Do you see incorrect values on your hardware CDU only, and correct values on the PSX server's computer monitor?

If so, maybe your PSX client for your FDS CDU screen is out of sync?


|-|ardy


P.S.: Maybe there are some misunderstandings. The FMC doesn't calculate your initial CRZ ALT. If you see a CRZ ALT of FL210 on the CRZ page in 1L, then you have entered this value yourself, or you loaded a company route that contains a CRZ ALT. In either case: That value doesn't come from the FMS computer.

Your PS sheds a completely different light on this matter. Indeed I had the impression that there was a "deep down wonder" taken place where the NG FMC was feeded with data from "PSX Dispatch" (but calculated within the software of PSX) I don't feed the NG with ALT data so I guess PFPX is in case of problems the culprit. As far as possible I tried to analyse a PFPX generated company route but I cannot find any information about CRZ ALT. Mysterious!
Ton

United744

  • Join date: Oct 2014
  • Posts: 911
Re: NG FMC calculations
« Reply #6 on: Thu, 4 Mar 2021 16:56 »
A quick rule of thumb for cruise altitudes: whatever your flight distance in NM, divide by 10 for short routes, and this is a good first-guesstimate cruise altitude.

e.g. 200 NM = FL200. 160 NM = FL160, etc.

The performance of the aircraft at low weight is high, so you can climb quite a bit higher in that distance, but you've got to get it down again. ;)

I don't much like PFPX beyond the basic route planning capability. The performance calcs are totally out of whack, and the fuel calcs are just broken.

I have tried to edit the performance database, but it is more trouble than it is worth. My "back of the envelope" calculations are more accurate!

Hardy Heinlin

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  • Join date: May 2009
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    • Aerowinx
Re: NG FMC calculations
« Reply #7 on: Thu, 4 Mar 2021 17:47 »
Hi Ton,

your PFPX route that you load in PSX is shown on Instructor > Situation > Human > Dispatcher, somewhere on that alphabetical route list in the middle of the page. When you click a route on that list, the related data is shown on the left side. It also shows whether a CRZ ALT and a cost index is stored in that route.

You can overwrite the CRZ ALT on the FMC CRZ page at any time. Just enter a value and execute.


|-|ardy

Ton van Bochove

  • Join date: Jun 2009
  • Location: EHAM/EHBK
  • Posts: 355
Re: NG FMC calculations
« Reply #8 on: Thu, 4 Mar 2021 18:27 »
Thanks Hardy!  I will check that out
Ton