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[SOLVED] VNAV on Descent not following speed restrictions in FMC


I9311I
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VNAV works great except on descent. It always defaults to 250IAS or less. I find myself manually setting the speed on descent for crossing restrictions frequently in the 280 range, then sometimes forgetting about it. Is that a bug or is it how it works in the real aircraft? 

Edited by I9311I
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3 minutes ago, leha74ru said:

if there are no constrictions on the LEGS page in terms of speed, then it will decrease according to the default profile 0.8/250. You can add these speed/height limits on the LEGS page

That’s what I’m saying. The speed restrictions, higher than 250, will be loaded and showing correctly in the LEGS page, yet VNAV descent will still automatically go to 250IAS at TOD. 

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9 hours ago, jetpipeoverheat said:

To add to Tom's post, you need to go to VNAV Setup and change your descent speed to be at or above the STAR speed restrictions. VNAV will not speed up to meet a restriction, but it will slow down. Planning a descent at 250 KIAS is painfully slow, both for your passengers and ATC. Generally .78/290 works well.

Ah, I get this now. Will it be persistent or will I have to change it every flight?

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6 hours ago, sunake said:

To add to what everyone else is saying. Speed restrictions on charts are usually at or less. So if the descent page speed is lower than the restriction on the chart, it wont speed up.

Not an accurate statement. Speed is usually a defined value. Altitude is usually a block.

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  • I9311I changed the title to [SOLVED] VNAV on Descent not following speed restrictions in FMC
22 hours ago, I9311I said:

Not an accurate statement. Speed is usually a defined value. Altitude is usually a block.

Ah thanks for the correction. I was thinking about the behavior of another aircraft type and forgot that not all SIDs/STARs with speed restrictions do not include MAX for the speed restrictions.

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