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FMC Fuel prediction on ground - quick question

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Hi there allIf I am on the ground, and I have everything entered in FMC, and it predicts I will arrive at destination with pretty much spot on what I planned to have - does it account for the fuel that will be burnt during taxi approximately, I should I add a little more fuel?Thanks for any help, regardsRudy


Rudy Fidao

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Use an external flight planner to determine fuel requirements, preferably one that takes weather into account and has the performance profile of the aircraft you choose. This will get you close. FSBuild 2 couples to weather loaded in Active Sky later versions. After downloading weather into ASV6.5 I construct the flight plan in FSB and export it to FS9 for loading into AS6. This refines the AS6 navlog produced by its import/process function. I print the weather navlog that gives me the necessary temperatures and wind vectors ground and aloft requested by the FMC. In the FSB aircraft profile I fill out estimated taxi time, holding time, extra fuel (again as time), time to alternate, and rebuild the plan (again exporting it to FS9 and the PMDG folder for the FMC (taking in the new refined AS6 weather) and it calculates the enroute time adjusted for the active weather.The FSB navlog then shows the calculated time and fuel burn for each phase and adds up all of the above. Remember that in the FMC the RESERVE entry is supposed to be fuel remaining after parking at destination which can either be a safety factor or depending on destination facilities fuel for the next leg. If the FMC estimates that you will be going into your FMC entered reserve you will get a fuel quantity warning. In some cases that warning may be premature during climb mode since you are using a higher burn rate for that procedure and you have not burned off the climb fuel weight yet. When you level at anticipated speed or go to economy climb the warning should cease. A look at the PROG page later in the climb phase should clarify any warnings.I like the breakdown of the FSB navlog fuel burn because in my 737NG you are supposed to land with minimum fuel in the center tanks. I therefore fill the center tanks with just 1,000 lbs over the FSB enroute calculation and the remaining tanks with the remainder of the total requirement.


Ron Ginsberg
KMSP Minnesota, Land of 10,000 Puddles
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To make the guess work easy on myself, I keep the reserve setting in the FMC at 50.0 when heading east. I also make sure that I have about 55 lbs(x1000) estimated to remain. When heading west, I usually set reserves at 30.0 and have about 60.0 estimated to remain. The east/west has to due with upper level winds. With tail winds, I usually have extra fuel (east). With a head wind, I end up with almost 20,000lbs less fuel than what was estimated (west).Once again, this is just for me and it's done so that I still land within weight limits and still have a very good amount of fuel onboard.Ryan Gamurothttp://www.precisionmanuals.com/images/forum/supporter.jpg


Ryan Gamurot
 

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Guest D17S

The FMC will only calculate the "Burn." The landing fuel you are seeing is just the "Burn" minus the fuel that is actually on board the airplane. The FMC's "landing fuel" is just that simple calculation of: Onboard - Burn = Landing (i.e., What'll be left!). This Landing fuel number absolutely meaningless unless you pre-fueled on the basis of . . . well, something. Here's a "something" that you can use: What I do is to load everything (route, winds, the works) into the PMDG FMC and let it calculate my burn. Use the FMC for this. There is nothing out there that does this Burn calculation as well as the PMDG FMC. It is the most accurate tool available. Make a note of this "Burn" number on a scratch pad. Then (if you want) use an external tool to calculate all the additional fuel required (alternate, contigency, taxi, etc, etc). Make a note of this number on a scratch pad too. Now: Add the burn (from the PMDG FMC) to the additional required and get a fuel load number. Burn + Additional = Fuel load. Then call the fuel truck and fuel to this amount.Prior to TO, make notes of the FMC's projected "Fuel remaining" at several waypoints on you route. Jot these down on your notepad. Zoom on.Now as you fly, the FMC will up date burn projection on the basis of how well the PMDG airplane is getting along with the MSFS atmospherics that day. Watch this carefully. Steve will tell you this is a big part of his job during these long flights. Make sure you are on schedule. This means the FMC's updated fuel burn projection needs to match the projection that was in place prior to TO (you have these noted on your notepad). Remember these pre-TO projections were the basis on which the FMC made its initial fuel burn calculation of the trip's burn fuel requirement. You fueled to this number + additional. If the FMC's inflight fuel remaining calculation starts getting less and less than your initial notes, wake up . . . and get ready for some real fun. And no, you cannot call the KC-10. No inflight refueling allowed!

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Sam is correct in that the FMC does a good job of flight planning. The only problem with the method described is that when you add all the extras on (reserves and contingencies) then the TOW of the aircraft increases (effectively a zero fuel weight increase) and therefore the fuel burn will be greater than originally calculated. I would suggest that you do as Sam has described to get an A to B fuel burn figure. Add to this fuel your reserves/contingencies. Now you need to make an allowance for extra fuel to carry the contingencies from A to B. As a close rule of thumb you will need to add an extra 100 kg of fuel for each 1000 KG of fuel carried over an equivalent still air distance (ESAD) of 1000nm. So if you had to carry an extra 8000kg of fuel over 4300nm then it would be (8000/1000 x 100) x 4300/1000 = 800 x 4.3 = 3440Kg.As you can see you will need to carry an extra 3440Kg to carry the extra 8000kg for that distance. If you work in pounds then you will need to convert from metric to imperial.You can use the FMC to calculate the ESAD. First of all load the route with no winds and note the flight time. Then load your winds and note the time difference to the no wind condition. Multiply the minutes difference by TAS/60. So if the TAS is 490kts then it will be 8.2 miles per minute. If you load the winds and it is going to take say 10 min longer than with no wind then add 10 x 8.2 = 82 miles to the flight planned distance to get your ESAD. Use this figure in your calculations above.CheersSteve


Cheers

Steve Hall

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Will the FMC in preflight note the added weight due to loading additional fuel and recalculate the predicted burn accordingly?


Ron Ginsberg
KMSP Minnesota, Land of 10,000 Puddles
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>Will the FMC in preflight note the added weight due to>loading additional fuel and recalculate the predicted burn>accordingly?>yes it doespaul

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Guest D17S

Good points throughout. Sure hope Mats hurries along with his flight planner. I assume it will incorporate the PMDG fuel flow tables. It'll sure be nice to have a button to press. . . http://www.vdispatch.ca/I generally steal old pre-flown flight plans for the 741/2s I deal. It just seems more fun to fly real plans. I use the crew

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