How many Altitudes should be manually entered. VNAV

So you have just chosen your STAR and approach and the FPL has an altitude entered at the start of the approach cone and during your descent. How many more altitudes should I enter into my FPL or can I just sit with the ones that are already entered?

Also, how do I know when to start/enable VNAV? I have been flying with altitudes in my FPL and I open the A/P Information and it says VNAV (3nm) then it says 2 nautical miles and then changes to 1 (nm) and then just says VNAV. Is there any other way to know when to start/enable VNAV?

Thank you everyone who helps with my questions.
Have a nice day and happy flying

I personally go by what I’ve been given right off the bat, maybe the odd edit of it here and there, but otherwise not really much more.

You can turn it on anywhere from no longer needing to ascend, or the recommended 1 minute before your top of descent. If you want to descend later, turn on VNAV later.

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Thanks, Is there any way to know when there is 1 minute until my TOD?

That’s beyond my knowledge right now.

If you want any further info, Tyler made a good topic on the use of VNAV put into a nice video.

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In the status bar, if you go all the way to the right with your finger. There should be something called “VNAV” I think 2 boxes up? That tells you when VNAV will have you descend if it is enabled.

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If you look at the VNAV button, you can also see how far your are from your TOD. 1 minute away is usually 5-10nm-ish

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This was kind of answered above but not explicitly so. When VNAV says 10NM, 5NM, etc, that’s telling you how far you are from your top of descent. When there’s no longer a distance there, it means you can still activate VNAV, but you’ll be descending at a rate that’s a little faster than the ideal rate because you’re past the “perfect” top of descent.

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