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3-2-1-Now

[MD-11] Calculating Fuel

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Hi,I can't find this anywhere. Vangelis said that the FMS computes this, but I can find anywhere how to do this??Best regards,Robin.

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In the INIT, Page 2, LSK R1, there's a section where you can enter how much fuel you're going to load up (BLOCK). You'll want to make sure INIT page 1 is done along with your FP before you try out different blocks, though. Your engines must be off for you to enter a block. To the left you'll see the various predictions for fuel burn. Put in whatever BLOCK you'd like and you'll see the fuel burn predictions change on the left side. Once your satisfied you can actually load up whatever amount of fuel you like, or if you need more fuel than you have onboard, use the CDU refueling option and let it do it for you.

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Hi,One better than that - if you go the refueling page and select FMS as the refueling source, it determines fuel load for you.Who said just pushing buttons didn't work? :7Best regards,Robin.

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Here is a quick && dirty guide :A. The FMS needs a certain amount of data to start trip calculations.In terms of fuel the following is required : trip fuel + fuel to alternate + 30 minutes worth of fuel for holding at clean speed at 1500 ft over the alternate. We also want taxi fuel (the default value of 700 kilos is enough for about 15-20 minutes taxi). We also require by law contingency fuel equal to 5% of the sum of trip fuel + fuel to alternate (JAR). On a long range trip you can legally reduce this to 2-3% since your real world filed flight plan will almost certainly feature an enroute alternate and redispatch point (too lentghy to explain what this is here but sure does save a ton or two of the hydrocarbon stuff). Finally it is prudent to require a little extra fuel. How much ? In real life it depends on all sorts of factors like expected weather on arrival, hour of day and expected traffic and so on. For simming purposes shoot for a reasonable 15 minutes of extra time on top of minimum fuel required unless you intend to fly online on a very busy event.Armed with all this information let us now fill in the data:1. Load flightplan, including SID and "a" STAR/APP procedure preferably. Enter also you desired alternate. By the way don't worry about remaining discontinuities and stuff (this is a really potent calculating machine).2. Time to go back to the INIT page (a) Enter your desired cost index (my favourite is 77 don't ask...) (:( Enter a cruise altitude. As you will learn the aircraft you will be able to guess your first flight level immediately. For your first flights enter some low-ish value like 320 or so. © Enter wind and temperature at altitude information if available. At minimum enter the overall tailwind/headwind component.3. Press PAGE to go to INIT page 2 (a) enter your zero fuel weight and zero fuel weight CG (or even better right click to get actual values) (:( You need an initial fuel guess : multiply hours to go by 8 tonnes (approx) per hour and enter this is in 1R. It is just a guess so it does not matter. Again as you will learn the aircraft your initial guess will become surprisingly accurate. © Edit the default contingency fuel value from 10% to 5% (enter /5 in the scratchpad and upload), or 3% for a long range flight (see note above)B. The FMS has now route, performance and weight information and will immediately start calculating fuel, ETO's (estimated time over), climb rates, descend rates etc etc. In short the FMS will perform a full mathematical simulation of your entire trip from takeoff to landing taking into account EVERYTHING related to the physics of flight, customised for this MD11 model and this simulator platform (FSX) and will continue updating on a very regular basis. C. At this point in less than a minute of our time we have a lot of data at our disposal. The PROG page tells us how much fuel we are expected to have at destination. A figure of 10-11 tons is good for almost 90 mins extra time allowing for an alternate within 100 miles, hold, contingency and more extra time. The INIT page shows us our first optimum altitude and maximum altitude at the present top of climb. Finally INIT page 2 provides a detailed fuel analysis. This is the point where we assume the position of a virtual captain rather than a real geek sitting on the virtual jump-seat keenly interested in "system-everything" but in the end expecting all critical decisions regarding OUR flight and OUR operation to be made by somebody else ! Financially speaking this is also the point where you get value for money by using the technology available and treating the plane in YOUR hands as what it really is : a very accurate model of an extremely advanced aircraft offering you a lot of resources for decision making.Performing refinements :(1) INIT page 1 : Check the current optimum altitude. Set as initial cruise level the nearest number (odd / even flight level). Example : if you are going west and the opt altitude is 345 round to 340. If the opt altitude is 351 round to 360. On a flight grossly speaking greater than 2 hours insert (candidate) step altitudes like so : 340/360/380/400 etc. The FMS will calculate and take account of all step points if and when available.(2) INIT page 2 : Check the extra fuel time down at L6. Too much ? Reduce fuel by approximately 2.5 tonnes per 20 minutes. Too small ? Increase fuel as required.(3) Everytime you change a number the FMS will immediately re-calculate your entire trip and provide new numbers. Use them !Now repeat steps 1-3 as required. As noted twice above you will progressively find that performance data initialisation and further refinements will take less than 5 minutes. The worse case scenario is a really long flight where you have to trade payload (reduce zero fuel weight) with fuel. Always check your landing weight.That's all. And many happy landings "in" the PMDG MD11.Vangelis===================================== E M V Precision Manuals Development Group www.precisionmanuals.com=====================================

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Thanks for that detailed explanation. Just one question arose on my last flight when I had a relatively close alternate and the 30 min minimum which is equal to 3.5 tons made me going below the 5.4 tons (3x1800 kg) and I got low fuel alarms on the way to the alternate. Therefore my question: Would you at least use an extra fuel that brings you from 3.5 to 5.5 tons at ALTN, so you avoid the low fuel warning. Or is this just a wake up call and the minimum for flying is much less and so no danger from a technical point of view on fuel feed to engines.BestAlexander M. Metzger

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The low fuel lights come on if any main tank is below about 4,000 lbs. It is only a problem if you didn't plan to on having that amount at that point in the flight. I'm not conversant with tons, but your fuel remaining on the way to ALTN should be enough for that leg plus an IFR reserve of 45 min (required for Part 90, assume it is too for Part 21, but this is what I use). I juggle the UFOB before the flight so that my excess time (after all allowances) is at least 45 min.Now, a 45 min reserve means you are going to have about 12000 lbs UFOB after landing at your alternate, which is 4000 lbs per main tank. Probably not a coincidence.I am just pulling numbers off the top of my head in this example, but it works for me.

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