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Precision Simulator update 10.120 (2 August 2020) is now available.
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Author Topic: No fuel calculation in FMC  (Read 216 times)

GodAtum

  • Join date: Jun 2014
  • Posts: 719
No fuel calculation in FMC
« on: Sat, 1 Aug 2020 23:32 »
On my flight from YSSY - KLAX, I'm getting no fuel prediction in the FMC (PROG page). AP is on with SPD, LNAV & VNAV PTH. At ACT ECON CRZ. Please see situ https://www.dropbox.com/s/s91c5623ck9tpos/save.situ?dl=0

Will

  • Join date: May 2009
  • Location: Chicago
  • Posts: 2032
Re: No fuel calculation in FMC
« Reply #1 on: Sat, 1 Aug 2020 23:51 »
Does it have something to do with the fact that your origin and destination airports are the same (KLAX) on the ACT RTE 1 page?
Will /Chicago /USA

Will

  • Join date: May 2009
  • Location: Chicago
  • Posts: 2032
Re: No fuel calculation in FMC
« Reply #2 on: Sat, 1 Aug 2020 23:56 »
Maybe this is all tied together but I can't solve the puzzle... but on VNAV, your OPT altitude is 331, your MAX altitude is 303, and the RECMD altitude is 290. I don't know how OPT could be higher than MAX.
Will /Chicago /USA

Avi

  • Join date: May 2009
  • Location: LLBG
  • Posts: 826
Re: No fuel calculation in FMC
« Reply #3 on: Sun, 2 Aug 2020 00:21 »
Quote
115.06. FMC: Fuel data indications are now blank when any route waypoint altitude exceeds MAX ALT.

Why the MAX ALT is so low is still a question.

Cheers,
Avi Adin
LLBG

Hardy Heinlin

  • Moderator
  • Join date: May 2009
  • Posts: 11756
    • Aerowinx
Re: No fuel calculation in FMC
« Reply #4 on: Sun, 2 Aug 2020 00:41 »
When the route is so short that the climb and descend paths almost intersect each other at an altitude below the performance related MAX ALT, the actual MAX ALT will be lowered for geometric reasons. Edit: Geometric reasons affect the OPT ALT, not the MAX ALT. So that's not the problem.

Why does this FMC route in that situ go from KLAX to KLAX (on the ACT RTE page)? How did you set up your YSSY departure stuff while KLAX was in the ORIGIN field? Now you can't delete the origin KLAX anymore without deleting the entire route. -- Luckily, you have another YSSY-KLAX route in RTE 2. -- Well, that doesn't fix the problem either ...
« Last edit: Sun, 2 Aug 2020 01:19 by Hardy Heinlin »

Hardy Heinlin

  • Moderator
  • Join date: May 2009
  • Posts: 11756
    • Aerowinx
Re: No fuel calculation in FMC
« Reply #5 on: Sun, 2 Aug 2020 01:10 »
I should be burning in hell; this is such a silly bug -- introduced by version 10.115. Unbelievable.

I'll fix it in 10.120.

Temporary solution in your situ:

1. Go to VNAV CLB page and enter 331 in 1L and execute.
2. Check that ECON speed mode is active on CLB page.
3. Enter 330 in 1L and execute.
4. Press the MCP ALT knob.

MAX ALT should now be FL362.


Background story: The bug was introduced by this modification:

Quote
115.05. FMC: MAX ALT displayed on CRZ page now refers to ACT CLB speed when CLB speed causes a lower MAX ALT than CRZ speed. This also affects the MAX ALT scratchpad message.

This modification should only run in ACT CLB, not in ACT CRZ. In that situ there's a hidden SEL SPD mode on the CLB page, and that SEL SPD lowers the MAX ALT even though we are in ACT CRZ. By reactivating the CLB, the SEL SPD mode resets to ECON mode which will not affect the MAX ALT.


|-|ardy

Hardy Heinlin

  • Moderator
  • Join date: May 2009
  • Posts: 11756
    • Aerowinx
Re: No fuel calculation in FMC
« Reply #6 on: Sun, 2 Aug 2020 01:37 »
Fixed now in PSX 10.120:

http://aerowinx.com/board/index.php?topic=4191.0


Sorry,

|-|ardy

GodAtum

  • Join date: Jun 2014
  • Posts: 719
Re: No fuel calculation in FMC
« Reply #7 on: Sun, 2 Aug 2020 08:47 »
Thanks so much Hardy, that's amazing! PSX is the best  ;D

Avi

  • Join date: May 2009
  • Location: LLBG
  • Posts: 826
Re: No fuel calculation in FMC
« Reply #8 on: Sun, 2 Aug 2020 12:57 »
I should be burning in hell;

As long as you are not exaggerating...
Avi Adin
LLBG