I received a note from Mark McGrath earlier today that provided a comparison between a FSBuild flight plan from EGPT to CYYC to a real world plan generated today. This is a flight of some 8 hours and provides some insite into one of the differences in 767PIC and the real world aircraft. The real world flight plan called for a destination burn of 38383 KGS with total block fuel of 45671 KGS. When he ran the plan with similar wind conditions and taxi, reserve, alternate, hold, and extra fuel to match, FSBuild calculated destination burn of 32328 KGS and block fuel of 39564 KGS. A difference of about 6000 KGS, or about 15 percent less fuel than the real world burn.My response to Mark was rather detailed and with his approval I thought I would share it with you. ______________________________________________________________Good stuff Mark. This was one of the things I learned very early in testing fuel burn with PIC. The PIC burns considerably less fuel overall than the real bird does. If you notice on the FSBuild FP, there is a CRZ BIAS of -10.3%. But that is not all there is to it. In FSBuild (the aircraft directory) there is a file called B763_PIC_Lbs.PRF which should only be opened from Notepad ->(If you open it by simply clicking on it your Outlook will get hosed up because that extension is misinterpreted as a mail profile

Mark advised me today that his original FSBuild flight was not run with the correct wind data. The actual FSBuild calculation was a burn of 35.8 and block of 43.3. Using those numbers, the FSBuild plan was 7% below the real world plan. That is much closer but the text in the original post is still all valid. I wanted to provide this information for those who might want to explore editing the BIAS settings for their long hauls. You should expect that PIC will burn at or just below the 35.8 number calculated in this case by FSBuild.Mike

Thanks for all your work on this, Mike!Lee Hetherington (KBED)

Hi,Thanks Mike for this detailed explaination. If possible it would be very helpful if you could post here the two flight plans ie. the one generated by FSBuild and the real life one. Your message points out several flaws we have to live with, one being the consistent optimistic fuel consumption of the PIC versus the real 767 and the other flaws being FSBuild limitations in terms of CI and complex climb performance tables.My guess is that there are smart brains out there who certainly will find a way to correct the fuel consumption discrepancy in PIC by playing with, God knows, which file: (air file?). Simulteanously I assume the developpers of FSBuild are aware of FSBuild's limitations and as always willing to look into possible improvements.Am I wrong?Michael

Thanks Lee, coming from you that means a lot! :)Michael,Those are great questions. I am unable to post the two plans side by side because of real world issues (SELCAL code and ident of the aircraft, etc). :( What really mattered was the bottom line DEST and BLOCK numbers that I listed.As for "flaws" with PIC fuel consumption, I am not so sure I agree. Perhaps I should quote from Mark."The FSbuild fuel burn was 35.8 and block was 43.3.This was 7% and 4.5% below the RW flight plan value.Considering that most airlines actively increase their flight plan fuel predictions by about 6% above the average consumption for each aircraft, I consider this to be close enough."That being said, PIC is very close to real world. Also, you have to consider that no two engines perform exactly the same. And as aircraft age, the fuel requirements begin to change. I like to think of PIC as a brand new bird that is fitted with two very clean engines. ;) As to adjusting fuel consumption in PIC (fuel scalars or whatever) I really do not feel the need and would be reluctant to change it. For one thing, anyone using FSBuild to plan a flight can count on the performance coming out very close. If some of us use altered 767 performance files, we would have to footnote all of our references to that effect and we would no longer be able to directly compare data. All of the sudden, we would have apples to oranges. I hope you see my point.The limitations in terms of fuel calculation complexity in FSBuild are well understood by Ernie and we have talked about it extensively. What it comes down to is this. FSBuild is leaps and bounds ahead of anything a flight simmer has ever had for planning a flight. It provides fuel calculations for PIC that is typically within a few percent of what you end up with. In Ernie

Thanks a lot for your reply. I do agree on both points. It was my mistake for not having read Lee's post. I also believe Ernie is right in his approach, sure enough he got other issues to solve which are of greater impact. I guess my thoughts were more on an academic level. However you brought up an interesting aspect of flight simulation which has not been tackled to the best of my knowledge that is the engine conditions. It would be interesting to know if a think-tank could imagine a way to compute engine usage (age, and other factors) based on the number of hours flown let us say on Avsim by a particular pilot. Then the user would have to take this computation into account when filing a flight plan. And here we may come back to FSBuild's capabilities to absorb such new factors.Am I going wild here?Michael

You're going wild here! :-)Lee Hetherington (KBED)

Mike,Which carrier was this flight plan from?

>>However you brought up an interesting aspect of flight simulation >which has not been tackled to the best >of my knowledge that is the >engine conditions. It would be interesting to know if a think-tank >could imagine a way to compute engine usage (age, and other >factors) based on the number of hours flown let us >say on Avsim by >a particular pilot. Then the user would have to take this >computation into account when >filing a flight plan. And here we >may come back to FSBuild's capabilities to absorb such new factors.I think the Engine conditions would be covered the Fsbuild's 'Bias' settings.Its likely the older the engines and airframe become older the less fuel efficient the aircraft will be. Adjusting the Bias percentage for age would probably cover this aspect. Regards.Ernie.

I will yield to Mark for that answer Ryan. I am not sure.Mike

Mike,Thank you. If it is from the same carrier I think it is, I may have an explaination for the relatively high flight plan fuel burn.Best Regards,

Sounds like a Zoom flight?

Ryan,New Canadian Airline ZOOM.Mark

First of all a big thank to Ernie for pointing to the CLB CRZ and DSC bias settings. This bring us back to the point which is how to define the % variance. As it was stated by Mike and Ernie the fuel consumption varies depending on the number of hours flown by the engines, airframe age and other factors. What I was thinking about is the following: If someone could create an application which monitors the usage of an aircraft in terms of number of hours flown, flight conditions, and whatever other parameters we may need and translate these datas into percentage figures available as % variance for input in FSBuild we would then have a close to real world flight plan. As it is now I have no way to figure out what % variance I must set in the Bias setting other than best guesses.Mike, if I may, I would like to go a step further in that direction and ask you the following: VATSIM keeps track of the number of hours flown by a pilot. Would it be possible for VATSIM to keep track of the number of hours flown by aircraft type for each pilot based on filed flight plans? If the answer is yes then VATSIM could have the % variance calculated and imposed to a pilot filing a new flight plan.Now one of the main issue here if I am not wrong is that a voluntary amended fuel consumption by way of modifying a flight plan can only be implemented if the .air file is modified accordingly. To modify the fuel quantity in FS or via a fuel calculator would not have the desired effect. Am I correct here?Makes any sense to you guys?Michael

Mark,Not the carrier I previously suspected. I am not familiar with ZOOM's flight plan format or software. Do they provide fuel flow or just fuel on board figures in the flight plan summary?Major airlines flight planning software is much more complex than any used for the purposes of flight simulation or even general aviation for that matter. I can only speculate that they uplift additional fuel to accomodate for ATC delays, significant weather or ETOPS. Air Canada often increases average the fuel consumption when they compute their flight plans ranging anywhere from 3%-10%. This is done to provide a safety margin as well as to provide extra fuel for any unforeseen circumstances.Best Regards,