Hello 

after PFPX has been released i have done a couple flights trying it out with the ngx . but i have noticed that i always get the fuel wrong . the difference sometimes is between 0.8 to 1.5 lbs (in thousands of course ^_^ ) so its a big difference . has anybody faced problems like mine or is it just that i need to change my fuel bias .

 

Regards

Hi,

have you checked pfpx cost index (C.I.) and cruise speeds vs ngx's ones?

 

Ciao

 

Andrea

Using the same Weather source?

Hi,

have you checked pfpx cost index (C.I.) and cruise speeds vs ngx's ones?

 

Ciao

 

Andrea

hello 

i always check the CI which in my case is 30 . and where can i find the cruise speed setting in PFPX ? 

Using the same Weather source?

yup . active sky 2012 

 

 

and where can i find the cruise speed setting in PFPX ? 

 

When you're on the page where you enter your CONT Fuel, REM Fuel, HOLD Fuel and all that, you'll see a speed in there somewhere (M84 or 0.84 or similar).  This can be overridden by a CI simply by typing the CI number.  This can also be set as a default in the aircraft's profile, if I remember correctly.

 

Your numbers have to match in order to question the validity of the plan...

When you're on the page where you enter your CONT Fuel, REM Fuel, HOLD Fuel and all that, you'll see a speed in there somewhere (M84 or 0.84 or similar).  This can be overridden by a CI simply by typing the CI number.  This can also be set as a default in the aircraft's profile, if I remember correctly.

 

Your numbers have to match in order to question the validity of the plan...

hello 

i went to the aircraft database and saw the part where it says default speed schedule it was set to m.78 so i changed it to 30 . i will fly a short flight and reply back . Thank you very much Kyle 

Regards

If you still have a difference you can manually adjust the fuel burn within PFPX. The manual explains how it is done.

 

 

When you're on the page where you enter your CONT Fuel, REM Fuel, HOLD Fuel and all that,

 

Wait, you actually have to ENTER that? I thought PFPX was supposed to take care of that for you. I have no time to calculate all that manually.

Arjen: It should compute CONT based on policy (10%, 5%, 3% I think are common?), but it does not have a way to compute extra and hold fuel by itself - you have to tell it how much hold to expect and how much extra you want to carry.

Wait, you actually have to ENTER that? I thought PFPX was supposed to take care of that for you. I have no time to calculate all that manually.

 

It'll calc all of that if you leave it blank.  I was just referring to the spot where you could override it if you'd like to.  As Peter mentioned, above, HOLD and EXTRA are more "tribal knowledge" fields.  As an example, if I'm flying to sEWaRk, on a day like yesterday, I'm going to add a good hour-ish of fuel to the HOLD box.  It's something a dispatcher would add from his knowledge of how the flight has been affected in the past.

It'll calc all of that if you leave it blank.  I was just referring to the spot where you could override it if you'd like to.  As Peter mentioned, above, HOLD and EXTRA are more "tribal knowledge" fields.  As an example, if I'm flying to sEWaRk, on a day like yesterday, I'm going to add a good hour-ish of fuel to the HOLD box.  It's something a dispatcher would add from his knowledge of how the flight has been affected in the past.

hello kyle 

as i told you yesterday i changed the cost index of the aircraft in pfpx to 30 . so im currently trying it out on a flight . the fuel estimates are spot on up to now . but i have another question if you dont mind . when flying the winds of certain waypoints change of course . so when i update the wind data in the fmc while flying will it change the fuel estimates from my original flight plan 

hope you understood me thanks

 

 

but i have another question if you dont mind . when flying the winds of certain waypoints change of course . so when i update the wind data in the fmc while flying will it change the fuel estimates from my original flight plan 
hope you understood me thanks

 

Hey Faisal - I'm not sure I understand the question, but I'll try to answer.

 

When you update the wind, the fuel prediction should become more accurate (especially in the cases you're using the predicted wind values from PFPX).

Hey Faisal - I'm not sure I understand the question, but I'll try to answer.

 

When you update the wind, the fuel prediction should become more accurate (especially in the cases you're using the predicted wind values from PFPX).

hello you kinda understand me . but what if it was a long flight and the winds of the waypoints would change direction alot will it then affect the fuel estimates in the fmc or not 

regards

 

 

but what if it was a long flight and the winds of the waypoints would change direction alot will it then affect the fuel estimates in the fmc or not 

 

Yes.  The FMC does not know what the wind is until you tell it.  If PFPX is planning for assumed wind, and you give the flight plan to the FMC without wind, there will be a large difference until you add the wind in.

 

If the wind then changes while enroute, the fuel estimates will vary proportional to the change in the wind data.  What this means is that if the headwind increases by one knot (relatively small), the estimated fuel difference will be relatively small.  If the headwind increases by 10+ knots (relatively large), the estimated fuel difference will be relatively large.  Wind doesn't normally change too drastically from the plan, however.

Yes.  The FMC does not know what the wind is until you tell it.  If PFPX is planning for assumed wind, and you give the flight plan to the FMC without wind, there will be a large difference until you add the wind in.

 

If the wind then changes while enroute, the fuel estimates will vary proportional to the change in the wind data.  What this means is that if the headwind increases by one knot (relatively small), the estimated fuel difference will be relatively small.  If the headwind increases by 10+ knots (relatively large), the estimated fuel difference will be relatively large.  Wind doesn't normally change too drastically from the plan, however.

hello kyle 

thank you for explaining this point . i just finished my 2.5 hour flight on the ngx and the fuel estimates where spot on ! but the only problem is that . when im about 15 nm away from the landing runway the fmc estimates are correct but when im about 5-7 nm away from the runway the fuel starts to decreases up to a point where its about .4 lbs away from the estimate which is weird 

regards