PMDG B77X & PFPX Fueling Figures

[Raphael_Chacon 42]

Hello Guys,

 

 

Sorry, its more of the same, but browsing around i dont find any precise solution for the fuel issue when planning with PFPX and PMDG 777.  I always run out of fuel........  I add a percentage more above the PFPX reccomendations, but whats the point of planing then......  :unsure:

 

I tryed the "FlyPrecisely" templates......   Not working,   recommends even lower fuel than original PFPX´s reccomendations for the same flight.....

 

Is the PMDG Fuel consumption ok?    I can see that some other external calculators are close to PFPX fueling....   Any clue?

 

 

Any recent solution?

 

 

Thanks in advance...   B)

[77west 139]

Hello Guys,

 

 

Sorry, its more of the same, but browsing around i dont find any precise solution for the fuel issue when planning with PFPX and PMDG 777.  I always run out of fuel........  I add a percentage more above the PFPX reccomendations, but whats the point of planing then......  :unsure:

 

I tryed the "FlyPrecisely" templates......   Not working,   recommends even lower fuel than original PFPX´s reccomendations for the same flight.....

 

Is the PMDG Fuel consumption ok?    I can see that some other external calculators are close to PFPX fueling....   Any clue?

 

 

Any recent solution?

 

 

Thanks in advance...   B)

Must be the way you are doing it - I always have around 8-14 tonnes remaining on landing, using PFPX. Are you using the correct template? Can you take a screen shot of the PFPX flight planning page and post it? 

[Raphael_Chacon 42]

Hello again,

 

Well i checked with the TOPCAT and other fuel calculators, and i get the same calculation as PFPX.  But PMDG B77X is higher than PFPX/TOPCAT, etc.....     I feel its happening from SP1B, or probabbly im doing something different?

 

Here the PFP Planing:

 

 

 

 

TOPCAT Calculation (Very simmilar as PFPX):

 

 

 

 

Well,  dont know whats wrong.....

 

I got to say that i used to plan my flights with PMDG B77X and PFPX, but i dont know whats different now.   I use V1.15, i Updated to PMDB B777 SP1B and this is TOPCAT V2.74b(Including the B772LR/F)....    

 

Any clue?    Or, is it a know issue?     I noticed there are many forum comments about it, but not a precise solution.....

 

 

Thanks in advance... B)

[77west 139]

 

 

Thanks in advance...

Wow, you really provided a lot of useful info! Thanks. Let me put those numbers into my own PFPX and see what I get.

 

 

Any clue? Or, is it a know issue? I noticed there are many forum comments about it, but not a precise solution.....

I calculated using same route with PFPX defaults and live weather and it gave me 175150lbs fuel. So it seems the 170-190K lbs mark is about right. Next bit of info is your fuel burn during the flight - do you compare it with the PFPX estimated fuel remaining at waypoint? If you print out the plan, you can actually compare exactly how much of a difference there is on your actual burn compared to PFPX. Also, when you planned with PFPX what weather data did you give it? If it thought still air and you had a 100kt headwind, that may make a difference. Also, where do you run out of fuel, half way or close to destination?

[pete_auau 1,159]

Obvious question is  that I see your using  lbs in pfpx  and  what weight units  are you using  in the t7 lbs or kgs?

[Shermann 4]

I think he uses LBS as 185000 kg is a bit too much he would give him an out of range error:D But topcat and PFPX not always match as PFPX take the wind in count while topcat doesnt.

[Big_Duke 11]

Also keep in mind TOPCAT is not a fuel calculator; it only uses the weights (including fuel) for calculating takeoff and landing performance.  Also, the PFPX OFP shown above indicates the trip average wind component as 0 Kts. Are you using the same weather source for planning as you use in FSX for flight? Unless you do, there will undoubtedly be a difference in fuel use. I have found the PFPX planning figures to be very close to FSX fuel consumption for both the 772 and 773, and have never come up short. Most times I'm actually a couple of thousand pounds over on arrival which is less than a 2% error.

[markadeane 272]

Fuel burn will vary depending on a range of environmental factors, but what I can say is that I've generally found the 777 actual fuel burn to be very close to the planned figures over a range of flights.

 

PFPX is a very complex tool, but used correctly it results in a flight plan that - in my experience at least - is bang on for flight time and very very close for fuel. As Jerry points out above, make sure that PFPX and FSX are using common weather values, as this would be the most likely source of your discrepancy.

[PatrickM 2]

Can you measure how much time FSX needs for one real minute? It happened to me that FSX needed 75sec for one real minute at normal simulation rate, but since PMDG calculats the fuel flow and some other parameters outside the FSX I run out of fuel halfway through the flight.. I know it sounds crazy, but that happened to me..

[Nyuni 1]

In your PFPX output I also see that you have 'LRC' for your CI value, which is what PFPX uses by default... What are you then using for CI? If you're not flying LRC in the aircraft, then the PFPX calculations are going to be completely off.

 

PFPX is purely garbage in/garbage out...

 

When I plan with PFPX, I always enter the CI I plan to fly with/enter into the FMC... And I find that the fuel loadout/burn is pretty much spot on. Try doing that and ensuring your in-flight winds aloft are appropriately reflected in FSX with whatever weather you prefer.

[scandinavian13 5,192]

 

 

PFPX is purely garbage in/garbage out...

 

Definitely.  I'm always amazed at how people don't pay attention to what they're doing in there and expect it to magically line up.

 

The picture you paint for PFPX needs to be the same picture you paint in the FMS during the flight as well.

[Richard McDonald Woods 168]

For the B77W I always use a CI of 120, planned and actual!, and use real-time ASN winds. So I shoud not expect any variation in factors at all.

 

In flying my sectors, I always record my times at each waypoint. These usually vary by only 1 or 2 minutes, even on long flights. PFPX planned fuel on landing is usually a little conservative, and I land with perhaps 5 tonnes extra on long sectors. Equally, I have not yet run low on fuel at any of the many re-dispatch points that I have overflown.

 

When we get TOPCAT support for the B77W, I shall expect very accurate take-off and landing performance figures, as I have experienced for previous aircraft.

 

Because I have had such success with PFPX, I can only surmise, as others have, that you have differences between your planning parameters and those encountered in the actual flight.

 

You will need to investigate further. Any further help will, I am sure, follow any additional input that you can provide.

 

Good luck!

Regards, Richard

[Raphael_Chacon 42]

Ohh,  Lot of responses,  Im sure that something will come out  

 

 

Ok, one by one:

 

Wow, you really provided a lot of useful info! Thanks. Let me put those numbers into my own PFPX and see what I get.

 

 

I calculated using same route with PFPX defaults and live weather and it gave me 175150lbs fuel. So it seems the 170-190K lbs mark is about right. Next bit of info is your fuel burn during the flight - do you compare it with the PFPX estimated fuel remaining at waypoint? If you print out the plan, you can actually compare exactly how much of a difference there is on your actual burn compared to PFPX. Also, when you planned with PFPX what weather data did you give it? If it thought still air and you had a 100kt headwind, that may make a difference. Also, where do you run out of fuel, half way or close to destination?

 

 

Yes, i print my FP after planning, im a longhauler, i really enjoy flying as precisely as i can(Im not an expert, but i try to learn as mutch as i can).   About the fuel consumption comparison during the flight, well, i actually have these written, and im reviewing that after take off, just passing KURTS ISEC i started to receive a difference of 4000 lbs(Not big deal), the i continue monitoring it  ......... later on at HILRD(2 hrs of flight aprox) i had 10,000 lbs less that supposed  ..........i continued monitoring........Few miutes after, at BLUFI ISEC i had 12,000 less and started to get the insufficient fuel msg, so i checked everything, but......no clue....  had to refuel in flight and see what was going on....  it continued burning more than expected........ :blush:        I got to tell you that i had about 50knts headwind at that point, some times less, but, i feel that running "insufficient" is not something normal at about 1/4 of flight i would say....    Ahhh, one more thing, the weather data i use is from ASN, for PFPX and for the sim of course.  Also i use the datalink figures in the FMC....

 

 

 

Obvious question is  that I see your using  lbs in pfpx  and  what weight units  are you using  in the t7 lbs or kgs?

 

Im using Lbs, i checked that part.... i got saved flights, i wnet through one of those and reviewed that.....  txs

 

 

Can you measure how much time FSX needs for one real minute? It happened to me that FSX needed 75sec for one real minute at normal simulation rate, but since PMDG calculats the fuel flow and some other parameters outside the FSX I run out of fuel halfway through the flight.. I know it sounds crazy, but that happened to me..

 

Well, i measured it, and i can say that they are exactly the same...60 sec FSX = 60secs real...............But, what did you do?    It would be interesting to know... :rolleyes:   

 

 

In your PFPX output I also see that you have 'LRC' for your CI value, which is what PFPX uses by default... What are you then using for CI? If you're not flying LRC in the aircraft, then the PFPX calculations are going to be completely off.

 

PFPX is purely garbage in/garbage out...

 

When I plan with PFPX, I always enter the CI I plan to fly with/enter into the FMC... And I find that the fuel loadout/burn is pretty much spot on. Try doing that and ensuring your in-flight winds aloft are appropriately reflected in FSX with whatever weather you prefer.

 

I have LRC because i was testing(After the flight) if i put something wrong on the PFPX, o i found that LRC filled more fuel on board than some other CIs available, but i normally use 50/85...   for this flight, i used CI85....i checked inside the plane using a saved flight,,,,,,,  anyway, the fuel different among those options is not significant.  still betwen the limits and thoughts you guys told me....i also calculated with PFPX

 

For the B77W I always use a CI of 120, planned and actual!, and use real-time ASN winds. So I shoud not expect any variation in factors at all.

 

In flying my sectors, I always record my times at each waypoint. These usually vary by only 1 or 2 minutes, even on long flights. PFPX planned fuel on landing is usually a little conservative, and I land with perhaps 5 tonnes extra on long sectors. Equally, I have not yet run low on fuel at any of the many re-dispatch points that I have overflown.

 

When we get TOPCAT support for the B77W, I shall expect very accurate take-off and landing performance figures, as I have experienced for previous aircraft.

 

Because I have had such success with PFPX, I can only surmise, as others have, that you have differences between your planning parameters and those encountered in the actual flight.

 

You will need to investigate further. Any further help will, I am sure, follow any additional input that you can provide.

 

Good luck!

Regards, Richard

 

Thanks Richard, ill try CI120 next time.    what i feel frustrated the most is that, i get the insufficient fuel, added 20,000 lbs, and then landed with 6000 less than supposed...even adding 20,000....   so, someething is happening i guess.... :huh:   By the way... there is a BETA version of TOPCAT with the B77X templates....check that out  B) 

 

 

 

Well, i will try another long haul and see what happens...

 

 

Thanks to all for your support....  I will let you know about next flight....

[77west 139]

 

 

Well, i will try another long haul and see what happens...

Sounds bizarre. Not something like forgetting to retract gear or flaps? I just cant understand how the fuel flow could be that off.

 

What are your actual fuel flow in lbs\hr or kg\hr during cruise?

[Markfl370 3]

Are you following the step climb in the flight plan?  If your altitudes are wrong it will affect your final fuel.  Also does your ZFW in PFPX match 777X?  As stated previously I find the fuel estimates in PFPX very reliable provided you have the CI, weight correct and you follow the altitudes.