Will try explain the dilema i'm having with fuel savings during my approach setup.

 

If i have 4t of fuel on board at cruise and my destination fuel on the FMC is 3.0t my GW is 60t and my LDW on my loadsheet is 57.8t and also on my loadsheet i expect to arrive with 2.5t

 

So to find my real LDW weight i subtract FOB with expected fuel at DEST, 4 minus 3 = 1t. 60t minus 1t = 59t

 

So my real LDW will be 59t. What will be my fuel savings?

 

Is this right - my fuel saving will be 1.2t - 59 minus 57.8 ?

 

Or will it be - loadsheet said i should arrive with 2.5t but FMC calculates 3t at DEST. Because of shortcuts due to ATC, TW etc. So i would save 500kg ?

 

Will it be,

 

A 1.2t

 

Or;

 

B 500kg

 

 

What will be my fuel savings?

 

In reality? The savings are best calculated off of the real numbers. The best way to evaluate this would be to write down what the DEST FUEL was approximated as prior to the shortcut, and then compare it to the DEST FUEL after the shortcut.

 

The paperwork could give you a rough estimate, but that's all planned, and acknowledged as 'not perfect' as evidenced by the ACT column to be filled in. It should be relatively accurate, but I wouldn't call it accurate for calculating fuel saved.

Even without shortcuts and following the planned route i almost always end up with a bit extra on long flights. So whats the best way to do this? Subtract fuel burn to DEST from GW and compare the LDW with the loadsheet LDW?

So whats the best way to do this?

 

Honestly?

 

Look at the PROG pages before you start burning fuel to see what your total fuel is. Note it.

Look at the PROG pages after shutdown to see what your post-flight total fuel is. Note it. (Also look at the totalizers to see what they claim you burned)

 

Compare between flights. (Compare totalizer data, too).

 

Any other method is bound to have a reasonable amount of error in the values.

Ok thats a good method, i will try that on my next flight. But what if you wanted to do it during cruise before descent?

Ok thats a good method, i will try that on my next flight. But what if you wanted to do it during cruise before descent?

 

Then you're really just running predictions, and predictions aren't a good metric for actual savings. It's one thing to use predicted savings when looking at routing options in flight (will my current route give me better savings, or should I take the other route...?), but it's another thing to use predictions to determine actual savings.

Yeh i suppose thats right, and having longer vectors due to a HEA your savings predicted before will be pretty much useless.

 

Do pilots have to note savings after landing at the gate? Well i assume they will do !

Do pilots have to note savings after landing at the gate?

 

They don't note the savings, though they may (depending on aircraft equipage like ACARS) write down the fuel in the paperwork for Ops, along with times out/off/on/in (OOOI times) and so on.

 

The airline would then calculate the fuel numbers on the ops level.

The companies can keep historical data and change flight plans as necessary. You're doing that, Vernon, when you note that you are under-burn on long flights. It sounds like your kg/hr rate is in need of tweaking.

 

If we are searching for shortcuts, we'll have one FMC on PROG 1 and one on the LEGS page so we can change the route and see how it affects the fuel and time.

In need of tweaking? Not sure what you mean! I thought PMDG modelled all this..

Correct, the PMDG NGX will allow you to do exactly as Matt mentioned. However, tweaking burn rates that he is referring to is in your planing tool (PFPX or whatever). You'll not change the simulated actual burn rate.

Yeh i use PFPX. What values will i use dan?

They don't note the savings, though they may (depending on aircraft equipage like ACARS) write down the fuel in the paperwork for Ops, along with times out/off/on/in (OOOI times) and so on.

 

The airline would then calculate the fuel numbers on the ops level.

 

Ok cheers kyle just need to workout a new BIAS like matt mentioned now. Defo ending up with too much fuel with flights over +1hr

Yeh i use PFPX. What values will i use dan?

 

Say you fly a route that is planned to burn 10.0 (unitless - lbs or kgs doesn't matter as we'll be using %s here).

You routinely land having only burned 9.8 of that planned 10.0 (say you've done this at least 5 times and you're burning 9.8 each time).

 

That's a 98% burn. You could then adjust your burn bias (in the aircraft profile in PFPX) to 98% to see if the resultant values match up better:

 

If it's only on flights over an hour, my thought would be that the cruise bias should be the only one dropped for now, but play around with it.

Nice to get caught up on this, but the reality is that approach and vectors from ATC will likely have more influence on your total burn than the absolute accuracy of your planning. You can fine tune via minutia record keeping during during climb, cruise, and initial descent, but even after doing so, the actual approach vectoring will likely have more influence on your end results. Reserve is there for multiple reasons.