VNAV descent question when approaching dest

[lineman55]

Ok, I know how to handle my descent altitudes using the MCP  as I approach my destination...but what I cant trust is the VNAV handling it by itself.It always seems to be descending to late in the leg..and wont slow down ..speed indicator does not match whats displayed on the CDU leg...

even with a strong head wind everything seems to be starting too late..and I have to intervene all the way to 2000' or my last waypoint.

Is it critical to enter any kind of wind direction and speed while setting up my  route while on the ground? Where would I find out this kind of info if im on the ground? I can see a wind speed/dir that is placed into the FMC where is it getting this info from? XENVIRO that I have?  Is the wind information/direction supposed to be displayed for each leg of the route?  I tried entering a wind dire/speed where it looks like I can but wont take it. I have been busy watching tutorials which are excellent..but Im wondering if Im missing something....Im all ears!
 

[Litjan]

Your observations are for the most part correct. For now, handle your descent with the MCP. We plan to improve VNAV in the future.

Jan

 

[lineman55]

1 hour ago, Litjan said:

Your observations are for the most part correct. For now, handle your descent with the MCP. We plan to improve VNAV in the future.

Jan

 

looking FORWARD to these improvements!  such an amazing aircraft ..so well done compared to what I have flown over the years in FSX and early XPLANE. Its one slippery bird!

[lineman55]

Last night I wanted to experiment..so I setup a short hop from KPVD to KLGA..FL110..ARRIVING using a STAR  for runway 04.

Fiddling around prior to takeoff I somehow managed to change my Target descent/speed from 278 to 210  and Lo n Behold! arrived within a manageable speed

that I was able to slow down within a respectable distance.I also find that If I change a particular altitude on a leg..the VNAV ignores that altitude difference in the flightplan.

The new altitude numbers stay bold..not matching the original flightplan text size..Is this normal? or is there a way to get it to fall into place so the VNAV will see it?

Edited January 17, 2017 by lineman55

[mmerelles]

2 hours ago, lineman55 said:

The new altitude numbers stay bold..not matching the original flightplan text size..Is this normal? or is there a way to get it to fall into place so the VNAV will see it?

how to read altitudes on the legs page:

XXXXXA (the aircraft must cross the waypoint at XXXXX or ABOVE that altitude

XXXXXB (the aircraft must cross the waypoint at XXXXX or BELOW that altitude

XXXXX (standard size not bold) estimated altitude computed by VNAV given your flight parameters

XXXXX in bold (user entered manually or procedure mandatory entered means the aircraft MUST cross at that altitude, not any higher not any lower.

 

hope this helps

[lineman55]

38 minutes ago, mmerelles said:

how to read altitudes on the legs page:

XXXXXA (the aircraft must cross the waypoint at XXXXX or ABOVE that altitude

XXXXXB (the aircraft must cross the waypoint at XXXXX or BELOW that altitude

XXXXX (standard size not bold) estimated altitude computed by VNAV given your flight parameters

XXXXX in bold (user entered manually or procedure mandatory entered means the aircraft MUST cross at that altitude, not any higher not any lower.

 

hope this helps

Thankyou...but I do understand what you mentioned..my question is how to get the VNAV to follow my Manual ALT input for that leg..it seems to ignore the altitude change because I manually inserted this ALT...UNLESS its precalculated and the text is smaller/standard with the rest of the legs.. I know I can do this with the MCP and a level change...but wondered if there is a way for the FMC to do this.

[TDPlane]

Be patient. The devs are working on an update of the VNAV experience ... As Jan points out, the VNAV calculation is only able to handle very basic scenarios for now.

Edited January 18, 2017 by TDPlane