No Descent Via VNAV

[berts 97]

21 hours ago, Captain Kevin said:

I don't think he actually knows Bob, I think he was just using it as an example. Probably make more sense reading it this way.

OK, Kevin.  In that case:-

Kyle, I think I can understand why you say the Bob you apparently do not know is remarkably vague about this subject.

 

4 hours ago, downscc said:

I notice the PFPX aircraft template I have for the -8 has one speed in the pull down box of 0.86 so I also use the FMC for fuel planning.  Just be sure to increase the fuel remaining prediction in the FMS to cover start and taxi.  I add 4 T... so if I want to have 12 T remaining I add fuel until the FMC reads 16 T remaining (presuming the winds are close to prediction)

You should not need to manually adjust the Fuel Remaining figure if the flight planning software you are using is doing its job properly, because changing the Cost Index should automatically adjust the various fuel amounts for you in your final Fuel Flight Plan.  It is normally good practice to leave the Cost Index alone during flight and simply vary the Cruise Speed or Mach No. manually in the FMS instead if you want to arrive earlier or later (there is also a LRC selection).  This is because the ACT ECON CRZ speed is based on the Cost Index.  The FMC usually uses the calculated value for performance computations and it will continually estimate the fuel remaining at destination provided the Active Route is flown. 

Another interesting point to  bear in mind is that the B744's fuel predictions are based on Flaps and Gear UP during the Climb, Cruise and Descent phases, so if you fly for any prolonged period with the Gear and/or Flaps extended then the FMC fuel predictions will not be correctly displayed in the FMC's fuel predictions pages.  Fortunately, if you do nothing about this you will get an INSUFFICIENT FUEL message to wake you up when you go below your Reserve Fuel value and probably long before you eventually run out of fuel!

Edited January 14, 2019 by berts

[vc10man 732]

33 minutes ago, Captain Kevin said:

On the flight planning screen, when you select an aircraft, you'll see Cruise/Cost Index. You can do it there. The profiles I have seem to allow 0 to 500.

At first I thought to myself, unh-unh, cannot see what Capt Kevin is referring to as my 'Add Flight' is cut-off at the bottom. It was only when I did not want to appear to be a total numpty and expanded that lower half, it became evident what you were alluding to.

Thanks, Captain.

Kudos to the OP for this really informative thread.

Edited January 14, 2019 by vc10man

[downscc 1,327]

3 minutes ago, berts said:

if the flight planning software you are using is doing its job properly,

And that is the big 'if'

The PFPX profile I have for the -8 has only .86 M and no CI values to choose from.  One has to improvise.

[berts 97]

Try using Simbrief because it allows you to experiment with the Fuel Plan figures in lots of ways, including changing the cruise speed and the fuel factor.  I suppose changing the latter is their equivalent of adjusting the Cost Index, although I haven't tried altering their default value myself.  

[Captain Kevin 586]

1 hour ago, downscc said:

The PFPX profile I have for the -8 has only .86 M and no CI values to choose from.  One has to improvise.

Which profile are you using. You won't find it in the drop-down box. You have to click it, clear the entry, and manually type it in.

[skelsey 765]

Hi Bertie,

2 hours ago, berts said:

Tut, tut, Simon.  Where's your respect for your Virtual managers?  😉

Besides, don't you mean the red band - and maybe the slower one was probably stuck at M0.76 because it was being held low and slow behind a Virgin A340?

I was thinking of the amber minimum manoeuvring speed indication -- as for the A340, given they only climb as a result of the curvature of the Earth I'd imagine it probably wouldn't have made it to cruising altitude by Mongolia!

1 hour ago, berts said:

Try using Simbrief because it allows you to experiment with the Fuel Plan figures in lots of ways, including changing the cruise speed and the fuel factor.  I suppose changing the latter is their equivalent of adjusting the Cost Index, although I haven't tried altering their default value myself.  

The Cost Index can be adjusted on the Simbrief flight plan data entry page. The fuel factor adjusts the overall fuel burn figures by the given percentage in order to account for the varying accuracy of FS models, amongst other things (just as real plans may have a fuel factor to account for increase drag/engine wear and tear etc as an airframe ages), so if you find that you are consistently burning more or less than the plan suggests you can make an adjustment here to take account for future plans.