Fuel planning

[ilovetofly 1]

Well I haven't recieved a reply yet as to my question regarding wind effect on fuel planning. So I'll add another question here and hope my figures can be corrected.PMDG 737-800KMIA-TNCM (Miami to Juliana)2h 36' flying time @ 39Kg p/min = 276 x 39 = 10,764 Kg (23,724 lbs.)Taxi fuel 240 Kg (530 lbs.)Holding fuel 1800Kg (4,000 lbs.)Contingency 10% = 1076 Kg (2,372 lbs.)Souls on board (w/luggage) 140 @ 102Kg (225 lbs.) 14280Kg (31500 lbs)Cargo 6,352Kg (14,000 lbs.) TOW after taxi 76,679Kg (169,000 lbs.)+ -Cruise Alt = FL370After setting up the FMC I'm seeing a balance of fuel @ TNCM of 5,762Kg (12,700 lbs.). I haven't entered the TOC winds nor the cruise winds into the FMC.According to what I understand here, I should arrive with only contingency fuel and holding fuel left, or 2,876Kg or 6,372 lbs., not 5,762Kg (12,700 lbs.).All of the conversions are not exactly accurate, but rounded off. So what have I done wrong here?Thanks for the help.Jim Dow

[Spin737 102]

I really enjoyed this thread. It sure helped in understanding fuel planning. I hope some are still following along, esp. Santiago.My question is in reference to the fuel consumption and wind direction. In the examples given, there was no calculation for wind speed nor direction. Does this mean it is not necessary to consider it? If it should be figured in,how would that affect fuel quantity?Jim D.

RW, here's how it works for the pilots:Show up at the gate, planning room, wherever, and take a look at your Computer Flight Plan (Howgozit, etc - whatever you want to call it).It's going to have your route, fix-by-fix.On each of these fixes, it'll have the time, fuel burns, winds aloft, etc. (The fuel burns are based on the time and the time is based on the groundspeed, which includes the winds.)You'll plug your route into the FMC and after that, you can plug in the winds for each fix.Now the FMC knows what altitude, what temperature and what the winds are, so it can guess what your fuel burns are going to be.So, your computer flight plan has the fuel burns based on altitudes, winds and temps, and your FMC has the same input.How does it affect fuel quantity? Headwind = more fuel, tailwind = less fuel. The flight plan should have that all worked out for you. In flight, you'll compare the computer flight plan to what is actually happening. ("We should have 21,000lbs at point XXXXX and we have 21,500," etc.) Stronger than expected headwinds might mean you won't have enough fuel. Stronger tailwinds might mean you'll be too heavy to land.Clear as mud? I'm a little sleep-deprived, so I'll work on an errata tomorrow. :(

[ilovetofly 1]

RW, here's how it works for the pilots:Show up at the gate, planning room, wherever, and take a look at your Computer Flight Plan (Howgozit, etc - whatever you want to call it).It's going to have your route, fix-by-fix.On each of these fixes, it'll have the time, fuel burns, winds aloft, etc. (The fuel burns are based on the time and the time is based on the groundspeed, which includes the winds.)You'll plug your route into the FMC and after that, you can plug in the winds for each fix.Now the FMC knows what altitude, what temperature and what the winds are, so it can guess what your fuel burns are going to be.So, your computer flight plan has the fuel burns based on altitudes, winds and temps, and your FMC has the same input.How does it affect fuel quantity? Headwind = more fuel, tailwind = less fuel. The flight plan should have that all worked out for you. In flight, you'll compare the computer flight plan to what is actually happening. ("We should have 21,000lbs at point XXXXX and we have 21,500," etc.) Stronger than expected headwinds might mean you won't have enough fuel. Stronger tailwinds might mean you'll be too heavy to land.Clear as mud? I'm a little sleep-deprived, so I'll work on an errata tomorrow. :(

Thanks Spin737, but I'm not a real world pilot and don't have all that worked out for me. I do have AS (Active Sky), but I'm attempting to follow the logic and examples provided by Santiago.Jim DowP.S. I believe that we are to use our real names on this board.

[Spin737 102]

Thanks Spin737, but I'm not a real world pilot and don't have all that worked out for me. I do have AS (Active Sky), but I'm attempting to follow the logic and examples provided by Santiago.Jim DowP.S. I believe that we are to use our real names on this board.

I amazed at how much realism some people can get with the various software programs and add-ons. Have fun!

[DC_Ed 3]

According to what I understand here, I should arrive with only contingency fuel and holding fuel left, or 2,876Kg or 6,372 lbs., not 5,762Kg (12,700 lbs.).

Hi Jim.Actually, you can use contingency fuel. It is there in case of longer taxi times, heavier than expected headwinds and that sort of things. You should arrive at your destination with reserve (or holding, whatever) fuel (30 mins international flight, 45 mins domestic) and alternate fuel (you're supposed to use it if you deviate to your alternate) which you missed on your calculations. :( If your current fuel is below the sum of those two values and you haven't arrived at your destination (or at least being in the landing traffic sequence) you are supposed to deviate to your alternate airport.

[ilovetofly 1]

Hi Jim.Actually, you can use contingency fuel. It is there in case of longer taxi times, heavier than expected headwinds and that sort of things. You should arrive at your destination with reserve (or holding, whatever) fuel (30 mins international flight, 45 mins domestic) and alternate fuel (you're supposed to use it if you deviate to your alternate) which you missed on your calculations. :( If your current fuel is below the sum of those two values and you haven't arrived at your destination (or at least being in the landing traffic sequence) you are supposed to deviate to your alternate airport.

Thanks. Yes I realize that I didn't include a reserve for alternate destination. I'll refigure and do the flight.Interestingly, I took out the PMDG manuals and checked the charts for fuel planning for the 738. For a 1200 NM flight@ FL370, the chart calls for 13.7K lbs.. Adding reserve fuel as dictated in a study guide for the 738 I found on the web, the figure was 4080 lbs and holding fuel 3300 lbs. After putting all this into the FMC I was WAY short and would run out of fuel far from the airport. So I added 5K lbs of fuel and the FMC liked that with a balance of 11.1K lbs. at destination. So my original figure was close even without the alternate fuel.I'm just trying to see the logic and results as described in the beginning of this thread. I'll try again.Jim Dow

[Guest mia]

Thanks. Yes I realize that I didn't include a reserve for alternate destination. I'll refigure and do the flight.Interestingly, I took out the PMDG manuals and checked the charts for fuel planning for the 738. For a 1200 NM flight@ FL370, the chart calls for 13.7K lbs.. Adding reserve fuel as dictated in a study guide for the 738 I found on the web, the figure was 4080 lbs and holding fuel 3300 lbs. After putting all this into the FMC I was WAY short and would run out of fuel far from the airport. So I added 5K lbs of fuel and the FMC liked that with a balance of 11.1K lbs. at destination. So my original figure was close even without the alternate fuel.I'm just trying to see the logic and results as described in the beginning of this thread. I'll try again.Jim Dow

Hi Jim,your calculations are nice... you only have to correct some things.I

[ilovetofly 1]

Thanks Santiago.I believe I now have it understood.Que' le vaya bien.Jim

[Guest mia]

Thanks Santiago.I believe I now have it understood.Que' le vaya bien.Jim

Un placer, Any Questions are welcome!Un abrazo!Santiago :(

[grimwlbbj 0]

Hi,I would just like to say a big thank you for every ones input and taking time to explain in great detail. I have learnt a great deal over the past month.Many thanksNatalie French