Question regarding VNAV's relationship with ATC

Hello Fellow Simmers,

As we await more aircraft equipped with fully functioning VNAV, I have a general question. First of all, I know how VNAV works, and have used it extensively in previous versions of FS, P3D and XPlane. But I have always wondered if in real life ATC knows when I any given aircraft is going to begin descending to a new altitude. My mind says that ATC “needs” to know so that potential mid-air collisions can be avoided. After all, we can’t just have airplanes descending “willy-nilly” all over the sky without ATC and other aircraft being aware.

ATC in FS2020 never starts descending me as I reach the TOD (Top Of Descent) in my flight plan. Sometimes they’re early, and sometimes they’re late. So I have two options. First, I can request a lower altitude as approach my TOD. But then I run the risk of being assigned to an altitude that is different from the altitude in the descent profile of my flight plan. Or second, I can play just along with whatever ATC says.

I suspect that in the real world, IFR Flight Plans filed with ATC include the altitudes for that flight, but I’m not sure. I also suspect that High Altitude Airways have something to do with it. Does anyone know how this works in the real world?

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Um, I fly the a320 in rl but no not really I mean the transponder does allow ATC to see your current altitude but typically you send a request over frequency to ATC if u would like to descend or climb to a new altitude assuming they take note of that

In the real world we don’t use VNAV unless we’re cleared to use it by hearing “Descend via the AnyName Arrival”. When that happens ATC expects us to descend soon (Top of descent calculated by FMS) and we start down and hit each altitude at a given waypoint on the arrival. VNAV can be used on approaches such as an ILS but not until we’re cleared for the approach otherwise the last assigned altitude must be maintained. For example, I was once on an arrival into LAX and 30 miles out we were cleared for the ILS approach. When that happened, the altitude at the GS intercept prior to the FAF was entered in the altitude selector so VNAV would take the airplane down to that altitude before intercepting the GS and then switching the nav source to LOC to fly the ILS.

Thanks Bril0ve, I appreciate the response.

Thanks for the input TCPD5091.

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