B767 VNAV descend

[Coanda F. Eckt]

How does the B767 VNAV manage say a thight STAR? Is it better than the B737 (which I've heard is not very good), or would you sometimes find yourself using FLCH or V/S to better manage speed and altitude constraints?

[pythagoras]

VNAV works fine, as long as you stick to the programmed route, the wind is as programmed and ATC let you descend as per your programmed profile. Otherwise you will need FL change and VS. Once you loose the VNAV path the FMC concentrates on descending the aircraft at the descent speed you set but will warn you if you won't make any height constraints.
I generally use FL change below 10,000' anyway as it gives more control when you inevitably stray from your programmed track

[ICEMAN757200]

I agree VNAV works just fine if the conditions parameters and atc are ok.I had some problem with Lnav but that is because som acft have gps update and some don´t .But anyway that´why we are there to monitor all things, if the aircraft is doing something wrong ,correct it ,if the autoflight sys is not performing properly ,fly manually.:) :ok:

[Coanda F. Eckt]

Ok, thanks. I get the impression VNAV PATH on Boeings (apart from 777?) is seldom used below 10,000' or at least flying a STAR with a lot of altitude and speed restrictions because it can be a bit unreliable, so instead VNAV with speed intervention or FLCH is preferred. Correct?

[extreme P]

Generally speaking VNAV will give you an altitude constraint but not the associated speed.

[Fliifast1]

50% of the time Vnav to the runway, flap selection will dial back speed bug and meet all constrants...when cleared to descend or cleared for an approach make sure you put field elevation or you will lose path to the runway...back to pilot stuff then. Lnav / Vnav approaches are about the laziest if you are the PF...just call for flaps,gear and checklists. Assuming you have autothrottles. B737NG. PHX Eagle1 Star is better if flown Lnav/Vnav. ATC will give you descend via the star, perfect.

problems come up with poor winds aloft or strong tailwinds on a star, level change works well then. 10-6 software has a glitch thats called Energy Conservation. humm 10-6a will solve that. When I see it dialing back speed I hit speed intervention and start looking for why.

[pythagoras]

Its not that VNAV is unreliable, VNAV gives the vertical profile based on distance to go based on your LNAV route. The minute you get a short cut you loose VNAV path. If you followed your programmed LNAV route all the way down, winds ok, ATC ok i'm sure it would cope fine. Just isn't flexible enough to cope well with the real world - but is it on any aircraft?