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Author Topic: Resetting VNAV phases  (Read 298 times)

Toga

  • Join date: Oct 2017
  • Posts: 228
Resetting VNAV phases
« on: Wed, 28 Oct 2020 18:51 »
Is there a way to reset the VNAV phase? For example if you were to 'accidentally' press '"DES NOW", is there a way to reset it to go back to VNAV CRZ?

Cheers.

Hardy Heinlin

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  • Join date: May 2009
  • Posts: 11985
    • Aerowinx
Re: Resetting VNAV phases
« Reply #1 on: Wed, 28 Oct 2020 19:40 »
Sure.

When you are in ACT DES, enter a CRZ ALT on the CLB or CRZ page.

When you are in ACT CRZ and you want to get into ACT CLB, enter a CRZ ALT on the CLB page.


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Toga

  • Join date: Oct 2017
  • Posts: 228
Re: Resetting VNAV phases
« Reply #2 on: Wed, 28 Oct 2020 19:51 »
Thanks. I presume it only works if you enter a higher FL/ALT than you are already at.

Hardy Heinlin

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Re: Resetting VNAV phases
« Reply #3 on: Wed, 28 Oct 2020 20:04 »
Not when you want to get out of the DES.

Toga

  • Join date: Oct 2017
  • Posts: 228
Re: Resetting VNAV phases
« Reply #4 on: Wed, 28 Oct 2020 21:46 »
I tested out pressing DES NOW when level in the cruise at FL370. VNAV then transitioned to the descent page as expected. With ALT mode engaged level at FL370 i then re-entered FL370 on the CRZ page and executed it. It just jumped back to the descent page. I tried also with the CLB page. It worked when I entered a higher FL than 370, FL380 for example. I was then able to enter FL370 on the CRZ page and continued on my way.

T

Hardy Heinlin

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Re: Resetting VNAV phases
« Reply #5 on: Wed, 28 Oct 2020 21:57 »
When your CRZ ALT is high enough and your distance to the destination is short enough, the FMC will activate the DES. You may get back into CRZ by re-entering the same CRZ ALT. But after a few seconds the FMC will re-activate the DES. This happens in the real FMC and therefore in PSX too.

In other words: When your new vertical geometry is such that the T/D is behind you, the FMC will activate the DES.


Toga

  • Join date: Oct 2017
  • Posts: 228
Re: Resetting VNAV phases
« Reply #6 on: Wed, 28 Oct 2020 23:22 »
Cheers Hardy!

Toga

  • Join date: Oct 2017
  • Posts: 228
Re: Resetting VNAV phases
« Reply #7 on: Thu, 29 Oct 2020 15:03 »
Hardy,

On some occasions - not all - i'm finding the FMC gets stuck in VNAV descent mode when executing a diversion to an alternate after a missed approach. I'm 51nm away from the diversion and only climbing to 8000ft. I go into the CLB or CRZ page and enter 8000 but it resets to the descent page again. I have found i'm able to put in a higher alt, say 9000, and it then resets to CLB phase. I can then re-enter 8000 and it's fine.
This doesn't happen that often but it has on some occasions. 

Hardy Heinlin

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  • Join date: May 2009
  • Posts: 11985
    • Aerowinx
Re: Resetting VNAV phases
« Reply #8 on: Thu, 29 Oct 2020 15:23 »
I can't comment as I don't know your exact situation and what exactly you're doing.

It's not only about distance to destination but also about waypoint constraints etc. pp.