VNAV Descent setup.

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rsyferd
Posts: 13
Joined: Fri Aug 11, 2017 9:06 pm
VNAV Descent setup.

Post by rsyferd » Sat Jan 18, 2020 9:24 pm

Hello,

I'm having trouble understanding how to set up the AP to follow the VNAV descent path. I've had the AP start and follow the descent path upon reaching TOD without any issues in the past, today it flew right past TOD without starting the descent. I had set the MCP ALT to a lower altitude as before and had and had a VALT indication above the PDF as before. What did I miss?

rsyferd
Posts: 13
Joined: Fri Aug 11, 2017 9:06 pm
Re: VNAV Descent setup.

Post by rsyferd » Mon Jan 20, 2020 10:34 pm

Had the same issue today. The aircraft over flew the TOD without initiating a descent.
First pic TOD is about 5 miles out. At 5 miles before TOD, VNAV has calculated a 1500 FPM descent and provided magenta bug on the VS display. Descent profile diamond has shown up to the right of the ADI. A TOD message has shown up just below and to the left of the ADI. I've set my ALT to 2,000 ft. The AP is in VALT mode.

Second PIC, the aircraft is about to pass the TOD. Just after that, the TOD and all the other indications I've mentioned above disappear, and the aircraft remains at FL280. Is there a missing step? The approach and its ALT restrains are entered and confirmed in the legs page as before which is required for the VNAV to calculate the TOD is the first place I believe.

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2020-1-19_12-49-27-102.jpg (235 KiB) Viewed 1111 times

rsyferd
Posts: 13
Joined: Fri Aug 11, 2017 9:06 pm
Re: VNAV Descent setup.

Post by rsyferd » Fri Jan 24, 2020 6:36 am

Any help on this?

KenG
Posts: 157
Joined: Sat May 09, 2015 2:33 am
Re: VNAV Descent setup.

Post by KenG » Fri Jan 24, 2020 12:48 pm

Did you press the VNAV button, did PATH arm in white?

rsyferd
Posts: 13
Joined: Fri Aug 11, 2017 9:06 pm
Re: VNAV Descent setup.

Post by rsyferd » Sat Jan 25, 2020 12:31 am

KenG wrote:
Fri Jan 24, 2020 12:48 pm
Did you press the VNAV button, did PATH arm in white?
When do I press the VNAV button. Just before I cross the TOD?

KenG
Posts: 157
Joined: Sat May 09, 2015 2:33 am
Re: VNAV Descent setup.

Post by KenG » Sat Jan 25, 2020 11:27 am

Anytime prior to TOD would be fine.


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