FMC - insufficient fuel error

[Guest lbb]

Hi Ian,"We" are referring to the PMDG user manual for the FMC. This makes for some interesting confusion: first, the PMDG manual does not describe how it would work in the real 737 and second, the PMDG sim doesn't work as described in the PMDG manual :-)I just made a flight from EHAM to EGKK and deliberately set the fuel reserves figure in the FMC to a ridiculously high number, with 7,100 kgs loaded I had set it to 6.9. I never got an insufficient fuel warning. So in that sense, while it may not be what the PMDG manual describes, that part does work as in the RW.However, I must admit that I did expect the FMC to give me the "USING RSV FUEL" message, but that didn't happen. Well, maybe in the 800/900?Leo Bakker

[Guest jase439]

The likely cause is that with long flights, slight changes in conditions - such as wind speed, current thrust mode, OAT, etc. create small variances in fuel consumption, which, when factored over the course of your entire flight are compounded and yield relatively large shifts in fuel consumption overall.The FMC only looks at your current atmospherics and does not account for conditions along your flight path. So if you were to experience a 10 degree shift in OAT (like you might find passing through an inversion layer), while it may be a "local" effect, the PMDG FMC would assume it to be a global change and update the fuel consumption for the entire plan as if those were the conditions for the entire flight. That would be my guess.Based on what the PMDG FMC manual states w/ regard to reserve fuel, I would try entering a smaller reserve value on the PERF INIT page and see if that buys you a greater degree of forgiveness.Ian: I was referring to the PMDG FMC manual in my quote above. I have no idea how the real NG FMC performs fuel consumption calculations, but I would presume it is far more sophisticated than the one modelled here.Good luck!J

[Guest lbb]

>Based on what the PMDG FMC manual states w/ regard to reserve>fuel, I would try entering a smaller reserve value on the PERF>INIT page and see if that buys you a greater degree of>forgiveness.Alas: nope. See my other post: the PMDG manual doesn't describe what the PMDG aircraft does.Still, good luck :-)Leo Bakker

[Qavion 19]

You may have to ignore the PMDG FMC manual, Leo (at least in this respect). From beta team conversations, I seem to recall that the SU-2 INSUFFICIENT FUEL msg was linked to predicted fuel at destination only (not RESERVE settings) I didn't know about the USING RSV FUEL message at the time, so didn't think to test it :-(As you say, maybe in the -800/-900's :-)Cheers.Ian.

[Guest Darren Howie]

G'day ThomasThe PMDG team are looking at this error.I posted a pretty comprehensive summary as to what was wrong and Randy said the eam are looking at it.I had the same problem as you with long flights and insufficient fuel.The fual calc by he FMC are "Incorrect" even over short distances like the next 2 waypoints.Lets see what happens.Take careDarren Howie

[fly_ebos 1]

Thx for the reply Darren, I thought I was the only suffering of lack of fuel ;-) Let's wait and see!regards,Thomas

[fly_ebos 1]

Hi,I just made a clean install of FSCOF + PMDG, done a long-haul test flight but I still get the insufficient fuel error. Although I've noticed that a flights stretching the limits (+ 3000 NM) I get it, but on 2800 NM flight everything works fine !regards,Thomas