I am posting this, hoping that somebody can clarify some fuel-related FMC messages that I have difficulty understanding.For relatively short flights (300-350 NM) flown at altitudes between FL270 and FL310 that I regularly undertake in the -600, as I complete the programming of the FMC, I continuously receive CDU messages that either the fuel is insufficient or that reserve fuel will be used for the flight.These messages puzzle me, because with a start up fuel load of around 60% (about 24,000 lbs), the fuel in the tanks at arrival is usually in the 10,000 – 15,000 lbs range.This has happened regardless of the altitude selected or the Cost Index selected (tried it from 15 to 90)I generally delete or ignore the messages and it is not often that a “reminder” is sent to me via the CDU during flight.I wonder if anybody could explain or clarify why it is that I am receiving these messages, considering that plenty of fuel remains in the tanks upon arrival.Thanks!Roberto

Hey Roberto!!!In Pre-flight PERF INIT page what are you setting as your reserve fuel? You could be entering a quantity higher than what you arrive with = using reserve fuelEg you set reserve fuel quantity as 5.0 however you arrive at your destination with 2.0Joel Fraseer

Hi Roberto - I use to get this message until I used a lower Reserve Fuel setting in the CDU.

Roberto, check this post out.http://forum.avsim.net/topic/340682-will-a-fsbuild-aircraft-performance-data-profile-be-available/page__p__2030378#entry2030378 Once you know your estimated fuel usage you can load the aircraft with the correct amount of fuel and thus input an appropriate resrve fuel setting.Hope this helps!!Joel Fraseer

I get the same and I'm pretty sure it isn't incorrect parameters.Fuel 15,000 lbs, trip 7,000 lbs, reserve 5,000 lbs, CI 40.By my mathematics 7,000 + 5,000 still equals 12,000 and is less than 15,000.......and 7,000 lbs quite accurate for YSCB - YMML.I disregard the messages as they only appear on ground, but I'm with Roberto on this.

Thank you everybody for your responses.I find myself in exactly the same situation as Graham.It appears that both of us use the same "mathematics" While I am an engineer, I don't trust myself with this "anymore" and I use a small calculator to ensure that the fuel quantities are correct.Yesterday, I landed with 21,000 lbs (as was predicted by the "PROG" page while en-route). The flight consumed 5,000 lbs and the reserve I chose was 4,000 while programming the route in the FMC/CDU, CI was 50 and I got the "Using Reserve Fuel" message, as soon as I selected the altitude of the flight (FL300).Roberto

INSUFFICIENT FUEL is issued when the arrival fuel is predicted less than 2000 lbs (about 900 kilos)USING RSV FUEL is issued when the arrival fuel is predicted less than the fuel reserve entry in the PERF INIT pageBoth messages require a valid FMC position, an active route an activated PERF INIT page and converged vertical path calculations for the active route.In thousands and thousands of flights that this airplane must have done by now, we have never heard of an issue related to such bogus warnings. The calculations are within 0.1 klbs if all data and forecast is entered correctly. I'd start searching settings and stuff, to begin with, on my PC/FSX.Note that the FMC does not have magical capabilities to imagine what fuel you intend to load and "sees" your actual (or during preflight the planned) fuel on board number as shown/enetered in the PERF INIT page (position 2L). Check these figures and we take from there.PS. Roberto if you read your last post it makes no sense man.

Hello EMV.I will make step-by-step notes of my flight planning and FMC programming and I will report back with the details, which will hopefully clarify what I am encountering.It might take a couple of days (it is the weekend) but I will report.Thank you for your interest.Roberto

No prob ! We are here to help since even 3000 pages of a manual would still not cover all the stuff in the NGx

Hello all:I was "allowed" to post it, before the weekend starts.Just did the following planning, programming:SLVR-SLCB (178NM, the FMC -with all the final approach routing, calculates it as 217NM) Route: SLCB VUROK SISER TIRKU CBA SLCBEstimated time en-route 00:48. Estimated fuel 4200 LBLoaded 60% of fuel, which resulted in 27610 LBZFW 97700 LBGW 125600 LBCalculated fuel as: 4200LB route, 2600LB for hold, 4200LB for Alternate (assumed return to SLVR) total required 12000LB, added 2400 LB (20%) for being a bad pilot, total required for flight 14400 LB In CDU, inserted 4.2 as "used fuel"In CDU, inserted 6.6 (4200 + 2400) as "reserve fuel"CI selected 50Flight level recommended by CDU FL 354; Flight level selected for flight FL260 (it is only :48 minutes!)As soon as FL selected, "Insufficient Fuel" message appeared in the scratch pad of the CDURetried with 10.2 inserted as "reserve fuel" i.e. the entire estimated fuel as reserve, got the same messageRetried, selecting FL340 as altitude and received the same "Insufficient Fuel" message.Obviously I appear to be doing something wrong, but I can't find what it is.Regards,Roberto

Oh I see. You insert in PERF INIT in 2L what you estimate will be your fuel burn (which is ;less than your reserves) . No no no.The number shown there is the sensed TOTAL fuel on board.If you want to enter anything (and only before takeoff) is a different fuel on board number in order to experiment with fuel load economy etc.Never your fuel burn estimate ! Obviously you tell the FMC I intend to carry 4.something fuel but I want reserves 6.6...You see whats wrong now ? Open this PMDG-NGX-FCOMv2.pdf and go to page 944 (manual page is 11.40.30) and read about it.PS. 27 klbs fuel for a such a short flight is BAD ! Furthermore the flight level suggested in PERF INIT position 1R is based on a 5 minute cruise minimum schedule assuming "normal" climb/descend path. It depends on weight/wind/isa deviation departure and arrival altitude and Its not there for fun.

Thanks EMV!I think that now I understand what I am doing wrong in placing the fuel burn rather than the fuel on board!I'll also read up the section you recommend.I'll test it tomorrow night!Regards,RobertoPS Yes, 14,000 - 15,000 would be more than sufficient for that flight with all kinds of sufficient reserves!