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 Post subject: request descent
PostPosted: Tue Feb 21, 2017 6:33 pm 
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Joined: Sun Sep 20, 2015 10:12 am
Posts: 34
I remember long time back someone had raised this issue of adding "request descent" option. I know that we can ask for lower altitude but is it possible to ask for beginning of descent?
Those who use advanced airliners with FMCs, it calculates descent point based on STAR, speed and cost index. Although PF3 usually is accurate in starting descent, in some situations, descent is delayed. Currently, only way to begin early descent to match VNAV profile is it ask for lower altitude. Is it possible in future to add request descent option?

Thanks


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 Post subject: Re: request descent
PostPosted: Tue Feb 21, 2017 10:19 pm 
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Joined: Wed May 27, 2009 8:41 pm
Posts: 955
Location: LIMZ
Quote:
I remember long time back someone had raised this issue of adding "request descent" option. I know that we can ask for lower altitude but is it possible to ask for beginning of descent?
Those who use advanced airliners with FMCs, it calculates descent point based on STAR, speed and cost index. Although PF3 usually is accurate in starting descent, in some situations, descent is delayed. Currently, only way to begin early descent to match VNAV profile is it ask for lower altitude. Is it possible in future to add request descent option?

Thanks
You are asking for two different instructions that in effect do the same thing. "Request descent" to what altitude? Can you see? If you request descent ATC will give you an altitude to descend to. And in any case ATC do not have to descend you exactly according to the FMC. They don't know or care about your cost index etc. What's in your FMS is nothing more than advisory and best economic flight profile. If ATC descend you late then that means you have a higher rate of descent. Quite normal. And here everyone has to put out the washing to descend very rapidly. All you have to do is recalculate your new descent profile in the FMC. It's what happens in real life every day and almost every flight.

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 Post subject: Re: request descent
PostPosted: Thu Oct 05, 2017 12:53 pm 
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Joined: Sun Sep 20, 2015 10:12 am
Posts: 34
I agree to what you but i was asking that if you can inform ATC 'ready for descent' then ATC will either start descent in usual manner or suggest unable at this time and start later.


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 Post subject: Re: request descent
PostPosted: Thu Oct 05, 2017 3:12 pm 
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Joined: Wed May 27, 2009 8:41 pm
Posts: 955
Location: LIMZ
Quote:
I agree to what you but i was asking that if you can inform ATC 'ready for descent' then ATC will either start descent in usual manner or suggest unable at this time and start later.
As stated before either ask for a lower altitude or adjust your fpl profile to be a closer match to your FMC. Again, ATC in real life are not interested at all in what your FMC tells you. It's up to you to inform them that you want to descend. PF3 already does quite a good job at calculating your descent. The fact that it doesn't occur at the precise moment your FMC tells you is immaterial.
If it is really really important that your descent must start at the moment the FMC indicates then adjust your fpl profile.
Even so you will probably never get an exact match.

Your points about making a request and for example ATC saying "unable" could be looked at as "unable at this time" does exist. The response exists but the request doesn't appear to.

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