Fuel miscalculation with PMDG 747v3 and PFPX

[JumboJet 11]

Good day !

This night I wanted to fly my PMDG 747 between Tel Aviv and New York, as usually I launch my P3D, then Active Sky 4 that I use for the Simulator weather and PFPX (My PFPX server subscription expired some weeks ago I maybe should buy a new one to solve my problem) and finally I launch PFPX for my flight plan.

I've never had any issues with the fuel calculation using PFPX (ok sometimes 1000 or 2000 lbs differences between calculation and fuel at arrival but not more), this night I had a miscalculation of 80,000lbs. The release was about to 283,000lbs and I had an insufficient fuel with 0,0lbs at KJFK all winds and route was in the FMS. 

 

So I've decided to change my fuel by myself before departing (I don't like the idea to swim in the Atlantic for the rest of the flight) and I was very surprised when I've discovered that, to get my 36,000lbs at KJFK I needed 350,000lbs.

I say again I've never had this kind of problem, my last flight RCTP - EDDF with the 747 was fine.

Sorry for my English I'm French.

Thanks by advance if you have a solution or a way to find a solution.

 

[Beardyman 604]

Jean, in my opinion PFPX do not calculate fuel correctly, leaving not sufficient reserve, and i have such situation every time i use PFPX and 747.

My simple solution without getting deep into numbers is to add extra 5 to 7T of fuel for short flight and 10 to 15T for long haul.

That will keep me always on safe side.

[SAS443 1,711]

Since PMDG recommends landing with at least 30.000lbs of fuel (13.600kg) because the HYD. Pumps are cooled by the fuel in the tanks, I usually tell PFPX that I want to have that amount of fuel left when I arrive. 

The only caveat (maybe I am doing it wrongly) is that the technique above seem to have null influence over release fuel with re-dispatch?

[Woozie 732]

Wow, 80k less is quite a lot. Did you import your FP from another source by any chance? Depending on the flighplan format, PFPX sometimes misinterprets (or ignores) NAT waypoints which would be the only reason i could think of that would cause such a massive difference. 

You may also want to double check your payload figures to ensure there's no typo.

 

21 minutes ago, SAS443 said:

Since PMDG recommends landing with at least 30.000lbs of fuel (13.600kg) because the HYD. Pumps are cooled by the fuel in the tanks, I usually tell PFPX that I want to have that amount of fuel left when I arrive. 

The only caveat (maybe I am doing it wrongly) is that the technique above seem to have null influence over release fuel with re-dispatch?

I assume you are putting this into the "Fuel remaining" field when planning the flight? You will find the same field in the aircraft config dialog, try to set the remaining fuel there. I always do it this way so i dont have to remember to add it during flight planning. I didnt see any issues with fuel re-dispatching using this method. May be worth a try

[iwebber 207]

Hmmmm, strange, I've rarely had PFPX out by more than a few percent.

What wind source do you use in PFPX? 80,000lbs short sounds like it was planned with nil wind and going west there's usually a headwind so when you put the winds in the FMC it calculated you were short.

IRL 30 mins reserve is about 4.5t, diversion around 5t and contingency around 1t so we usually plan to arrive at the destination with about 10.5t (or just over 23,000lbs in old money)

Hope this helps,

Ian

 

[fluffyflops 1,845]

pfpx is really good.  Ill go with Ian maybe the wind data,  and nice to see someone knows about the differences with reserves and contingency most of my new crew dont !!!  

you do know the north atlantic winds are very strong this week ??  that could be your problem.  going West times are longer and then coming back east its alot shorter. 

Its caused us issues in work with slots.  for example theres restrictions and penalties on slots in EGKK before 6am so flights back from the Caribbean we have to run the plans at a slower mach speed or tell the grumpy crew not to push back in BGI,UVF and ANU until a certain time and then acars ops with a estimated landing time at LGW to not land before 0600am to avoid the penalty. 

Another example the vs15 from gatwick to orlando today is 09hr 30 mins flying time.  Its an extra 45 mins to what it normally is in summer.  Thats one of the reasons airlines "pad" their schedules..  

your flight yesterday was filed at 1137 take off to touch down and thats at mach .85.. he battled the wind. and the winds today I believe are stronger

(FPL-ELY001-IS
-B744/H-SDE2E3FGHIJ7LM3ORVWXY/LB1D1
-LLBG2300
-N0499F300 MERVA UP42 DESPO UR18 ALSUS UB15 VESAR UB545 MUT UL621 ODERO DCT IRDUM DCT BUKOV/K0928F320 L621 ABSON/N0502F320 L621 GOTIX DCT MOTAD N133 PENOR DCT MOGLU DCT DIDAX/N0490F340 DCT TUPUV/M085F340 DCT 64N000E/M085F340 66N010W 67N020W 67N030W 66N040W 63N050W DCT URTAK/N0486F380 DCT DUVBI DCT YZV DCT TAFFY DCT ENE PARCH2
-KJFK1137 KIAD
-PBN/A1B1D1L1O2S2 DOF/180116 REG/4XELC EET/LCCC0011 LTAA0037 LTBB0129 LBSR0136 LRBB0146 UKBV0224 EPWW0245 ESAA0335 ENOR0407 ENOB0447 BIRD0459 66N010W0533 67N020W0603 67N030W0631 BGGL0635 66N040W0701 63N050W0741 CZQX0757 URTAK0827 CZUL0924 CZQM1001 KZBW1011 KZNY1130 SEL/HMCK CODE/738043 RVR/200 OPR/ELY ORGN/LLBGELYW PER/D TALT/LCLK RMK/TCAS II EQUIPPED)

coming back, he did it in 10 hours 11 minutes...  my guess maybe the wind data ??

 

 

[downscc 1,327]

I use 12T as a minimum fuel at destination value, which is sufficient for hydro cooling.

An error of 80,000 lbs sound more like an error in the route planning.  It is easy for PFPX to select a fix that is a continent away from intended fix, always double check.

[BlueStar 323]

13 hours ago, Beardyman said:

Jean, in my opinion PFPX do not calculate fuel correctly, leaving not sufficient reserve, and i have such situation every time i use PFPX and 747.

I don't have a problem with PFPX.  I just did EDDF-RJAA where my flight time was with 5 minutes of planned ETE of 10 hrs 35 min.  The calculated fuel was 295,000 lbs and fuel was off by 5,000 lbs.  

If the B744 is flown as designed it will be close to what PFPX calculates.  

blaustern 

[cmpbellsjc 2,960]

20 hours ago, JumboJet said:

Good day !

This night I wanted to fly my PMDG 747 between Tel Aviv and New York, as usually I launch my P3D, then Active Sky 4 that I use for the Simulator weather and PFPX (My PFPX server subscription expired some weeks ago I maybe should buy a new one to solve my problem) and finally I launch PFPX for my flight plan.

 

There’s a few things I noticed in your sequence that seems to be out of order according to what I’ve read, not that it will make a difference but might be  a better way.

First start AS4 and let it load the weather. Once loaded start PFPX and if you have it set up to take the weather info from AS4, all the wind and weather info will be up to date. Once you build the flight plan export it to the PMDG folder and close PFPX. At this time you can either load the flight plan into AS4 as well or let PMDG load it via the FMC function. Open P3D and begin flight. You don’t need to keep PFPX open at this time.

If your getting your weather in PFPX from AS4 then it shouldn’t matter if the subscription is expired except for the NATs I believe.

[DEHowie 269]

Wow an airline who plans to turn up anywhere with just enough gas to cover the hydraulic pumps..ouch.

So on short final into JFK and the aircraft lined up has a tech issue around you go. In the A330 we plan on 3 tonnes for a full vector to land off a missed with CF6's so lets call it 6 tonnes in the jumbo.

You plan on arriving with 13.8-12 tonnes and boom around you go and now your landing with 6-7 tonnes with the hyd pumps flat chat pulling flaps up and down plus the gear..just what you want minimum fuel hyd pumps overheating what an awesome situation to find yourself in.

Not only do you barely have 30 minutes but you have ZERO time if anything tech happens to the aircraft in the subsequent circuit back to the ILS.

Feel free to put the mayday mayday mayday fuel call in to get priority in the queue but the chief pilot will know by the time you have turned off the runway and your one way ticket to head office to explain what you where doing going into a busy airport minimum gas will be waiting you...lol. And priority doesnt help cover the track miles to get back to the IAF to sttart the approach again.

Just take a good packet of biscuits for the meeting ive heard it makes all the difference...

We call them fuel tanks not air tanks...

 

 

[Litmoose 90]

are you sure you didn't just get KGS and LBS the wrong way around? using 80,000 extra seems a bit excessive

[fluffyflops 1,845]

funnily enough of our our a/c's couple of weeks ago had to to do a pan into JFK.  (I was working that day it caused a right old ruckus in the office as we had senior management in observing that day as it was the bad weather they had in NY.) 

On approach they where changed runways 4 times from the handover on the 3rd time the skipper said "if you change us again we will have to pan" a few minutes later they changed and he panned. The ASR that came in for makes for brilliant reading , We get loads of ASRS for the place

[simbio 56]

Can someone post PFPX setting for the airframe?

This is mine for the 400F

[iwebber 207]

8 hours ago, DEHowie said:

Wow an airline who plans to turn up anywhere with just enough gas to cover the hydraulic pumps..ouch.

Easy Tiger, there are no hydraulic pumps in the fuel tanks and the airline has been operating this type for over 25 years, do you know how many hydraulic pumps they've lost due to low fuel? The answer rhymes with hero.

8 hours ago, DEHowie said:

So on short final into JFK

Even the company doesn't give us minimum contingency going into JFK and I've yet to fly with anyone who doesn't take more.

8 hours ago, DEHowie said:

Not only do you barely have 30 minutes but you have ZERO time if anything tech happens to the aircraft in the subsequent circuit back to the ILS.

No, you have 30 minutes reserve and your diversion fuel + whatever contingency you didn't burn in the go around, that could still be quite a bit. As to another tech problem, of course it's possible, but where do you draw the line. You've already had one unexpected incident, chances of another one? how about another? And another? You can't take enough fuel for every situation... what about if the wings fall off? eh? what about it? what would you do then, punk! you and your cowboy airline... Get's a bit silly doesn't it.

Our system gives us 95% statistical contingency fuel which means the company plans on enough extra fuel to cover 95% of all the extra fuel other flights to that destination, around that time at that time of year burnt. 95% of the time it's enough. As pilots, we're there to try and identify whether we think there's something going on that pushes us into that top 5% where we need more, in JFK, there usually is, so more is taken.

Most of the time we don't hold and there is minimum delay (even into JFK), not touching most of our contingency and our diversion and reserve fuel, in fact, the only place we hold with any certainty is LHR and most of our contingency gets burnt on the ground at LHR waiting to take off.

8 hours ago, DEHowie said:

Feel free to put the mayday mayday mayday fuel call in to get priority in the queue but the chief pilot will know by the time you have turned off the runway and your one way ticket to head office to explain what you where doing going into a busy airport minimum gas will be waiting you...lol. And priority doesnt help cover the track miles to get back to the IAF to sttart the approach again.

If we'd taken the fuel the company told us to or more there would be no issue, except for arguing over who fills out the ASR and if by some quirk they wanted to talk to us about the event then biscuits would be provided.

This is all perfectly normal, legal and sensible, I'm stunned someone who actually flies can find a problem with it, are you sure you're not a journalist?

Just trying to add some calm, hyperboleless (real word?) real life info,

Ian

[downscc 1,327]

I rarely plan a flight where the fuel remaining has anything to do with the recommended minimum of 12T (or 22,000 lbs).  On this subject, I just finished the UPS32 B744F KSDF-PHNL trip.  Fuel released 247,147 (lbs) and planned fuel remaining 32,200, actual fuel remaining 31,100.  I think this qualifies and being spot on.  The fuel remaining represents contingency and alternate (PHKO) planning, and rarely has anything to do with the desire to not uncover the hydro heat exchangers in tanks 2 & 3.  I used PFPX and ASP4, ZFW was 616.2 klbs.