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Paul_Yorks

VNAV speed reduction

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I use RC4 with the NGX, so I need to ensure I hit about 11/12,000' by 40m out from my destination.

 

I use a combination of v/s and vnav to get down.

 

If I am in vnav, and hit my target altitude early, as one tends to do I find that my speed then starts to drop - quite a lot.

 

Looking at FCOM 2 I see in section 11.31.30 this: "The FMC uses a special program called “Energy Compensation...” etc - so it looks like vnav is shaking off speed, to make the resumed descent easier.

 

Is that what is likely happening here?  I think so, but would like to clear it up.

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In real life they go to flight level change on descent, about the same time that you have this problem. Then speeds should be entered manually

 

RGS,

 

Yori Smulders

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If you enter energy conservation, it means you're too high. You should see the path indicator below.

 

It's not required to go to LVL CHG by any means. That's one way of doing it. If you are on vectors, that's a good way of handling the issue. If you're follow a STAR or and arrival route of some sort, it might be better to stat in VNAV.

 

You need to request lower sooner so you don't end up high on path.

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That's RC4.3: 11k/12k still when only 40 nm out ... but RC vectors you around a lot, so you can lose some ALT after contacting. approach.

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