I changed the ZFW in the 767 aircraft.cfg file from 245 to 286 in order to performe some flights with that calculated higher ZFW. Howewer, I can now enter both 245 and 286 in the PERF INI page without getting an error message when entering the lower weight. This results in quiet big errors between fuel calculation and real consumption, up to 7 tons on a transatlantic flight without changing wind conditions. May I therefor ask: where and how exactly do I have to change the value for ZFW in the cfg.file to actually get the airacraft having the "new" weight?

Hmmm .. unless I am missing something you can enter whatever ZFW you want on your FMC - FMC has no independent way to verify your weight. How would FMC know what your ZFW is in order to give you an error message :-hmmmThe key is that both ZFWs (entered in the file and in FMC) must be identical. And you better not lie to FMC .. :-eek Michael J.

And you better not lie to FMCWell...you can lie to the FMC, but it pays you back by lying to you for the rest of your flight. Bad V speeds, bad fuel calculations, etc.Garbage In, Garbage Out as the saying goes...Jon (KSEA)

In the PIC767 I always was getting an INVALID ENTRY message when entering a ZFW different from theone in the aircraft.cfg file...

Are you entering the weight in the same units as you have set FS?If you are using the Metric System you must enter the weights in Kilos, while if you are using the US system you must enter then in pounds.So, with metric system, the ZFW of 245,000Lbs should be entered as 111.1 Tonnes into the FMC... Simple convert the weight to KilosKgs = Lbs * 0.4536Fly safe!George DorkofikisAthens, Hellas

Yes, I always enter weight in the right units. As stated, the problem is not that the FMC doesn

Sorry, I can't really understand where is your problem!You say that you change the ZFW in the aircraft.cfg. Ok, this is the proper place to change it. Then you enter it to the FMC and it accepts it. So where is the problem?!Can you be a bit more specific please?George DorkofikisAthens, Hellas

Yes, one more try. You say right, the FMC accepts the new value entered in the cfg file. BUT, he also accepts the old (lower) value! Why that?

The FMC will accept ANY value unless it's too low or too high.

Ok, got you now...FMC will accept ANY value as long as it is within the operating range.That is Greater than the Basic Weight of the a/c (BW) and less or equal to the Maximum Zero Fuel Weight (MZFW) of the a/c.ZFW = The aircraft gross weight loaded with passengers and cargo but without any fuel onboard.MZFW = The maximum possible value of the above... Above that, the a/c is overloaded and you will have to remove load.It does NOT read the weight in the aircraft.cfg.It's YOU, the PILOT who will have to 'tell' the FMC what is the ZFW.However, it's advisable to always enter the correct ZFW in the FMC, otherwise it will calculate wrong speeds, fuel burn, EETs etc...In simple words, if you put in a wrong ZFW, NONE of the data displayed by the FMC will be correct.Hope this makes it clear.George DorkofikisAthens, Hellas

Yes, you made it clear. I should have tried to enter much more different values before, now I see that I can enter everything between 82 and 130 tons, having 130 tons as ZFW in the cfg. file :-eekThanks a lot for your help!

Not quite right about the max input range:It is, indeed, limited by max ZFW but also by max takeoff weight.So if you have a low fuel weight, you can enter max ZFW (around 288,000 lbs). If you have around 150,000 lbs of fuel on board, the max ZFW it will accept will be around 258,000 lbs (MTOW is 408,000 lbs)

Boeing shows the Operating Empty Weight for a 763ER as 90,540 kg. and the Maximum Zero Fuel Weight as 133,810 kg. So in theory, one could enter a ZFW of any weight within that range. However, 767 PIC is designed to carry maximum fuel load without exceed Maximum Takeoff Weight so for practical purposes the upper limit for ZFW in 767 PIC is less than stated by Boeing. As you pointed out, the key is to ensure that the ZFW in the aircraft.cfg file and the entry into the FMC are the same.

Correct!!I did not mention the MTOW (or even RTOW) so I don't confuse the readers more. :-)They are all connected. You may be below MZFW but with the fuel load required to make a flight, the wx conditions (too hot etc), the runway condition etc, may end you up with eight above the Max or Regulated/Reduced Take-off weight...In this case, you have to choices... Either offload pax or cargo, or make a fuel stop somewhere in the way! :-)A/C weight & balance is one of the most complicated and most important issues of the pre-flight preparation.George DorkofikisAthens, Hellas

In your aircraft.cfg (make a backup copy!) you can edit empty_weight to set the ZFW. The reason it is so simple is that there are no weight stations used in PIC. In some aircraft the ZFW is then the sum of the empty_weight + any station loads (e.g., passengers, cargo, etc.).This value is always lbs, regardless of the metric setting in FS. You can see the default value of empty_weight=245xyz right in your file.Lee Hetherington (KBOS)