How to calculate the Estimated Fuel Enroute
(EFE Fuel Consumption) for a Flight Segment.
1st Step: Determine the segment distance (Dist) for the flight using aeronautical charts or tables giving distances between airports.
2nd Step: Determine the segment cruise groundspeed (GS) – use your E6B air navigation computer and the forecast temperature and wind at your cruise pressure altitude, or use your personal knowledge of the aircraft true airspeed and your accurate estimate of the headwind or tailwind component at your planned altitude.
3rd Step: Look up the segment climb/descent data (DTC, DTD, FTC, FTD) and cruise fuel flow (FF) with reference to your planned power setting and cruise altitude (see list below) – use your Aircraft Flight Manual (AFM) Performance Section.
4th Step: Calculate the specific fuel consumption (SFC) during cruise. [SFC (Nm per Pound) = Cruise Groundspeed (Nm per Hour) divided by Cruise Fuel Flow (Pounds per Hour.)]
5th Step: Estimate the number of minutes for takeoff and departure (TDF), approach and landing (ALF), holding (HF) and taxiing (TF). To calculate the fuel used (pounds) for each of these, multiply the number of minutes in each case by an appropriate percentage or multiplying factor of cruise fuel flow (FF) divided by 60 (Pounds per Minute).
Method 1 (Primary Method) – EFE Fuel Consumption
The general formula for determining the Estimated Fuel Enroute (EFE Fuel Consumption) is –
EFE(1) = ((Dist – DTC – DTD) / SFC) + (FTC + FTD + TDF + ALF + HF + TF)
Dist = Segment Distance (GCNM; i.e., 134.)
DTC = Distance-to-Climb (Nautical Miles; i.e., 41.2)
DTD = Distance-to-Descend (Nautical Miles; i.e., 56.5)
SFC – Specific Fuel Consumption = GS/FF = 0.310 Nm/Lb.
(GS = Cruise Groundspeed (Knots; i.e., 273))
(FF = Fuel Flow (Cruise) (Pounds per Hour; i.e., 881))
FTC = Fuel-to-Climb (Pounds; i.e., 333)
FTD = Fuel-to-Descend (Pounds; i.e., 184)
TDF = Takeoff and Departure Fuel (Pounds; i.e., 56)
ALF = Approach and Landing Fuel (Pounds; i.e., 70)
HF = Holding Fuel (Pounds; i.e., 29) – (Holding Minutes = 2)
TF = Taxiing Fuel (Dep Taxi + Arr Taxi) (Pounds; i.e., 293)
(Note: The above numbers are based on a flight from SAC to FAT in a CE-500 at FL230. ETE = 42 minutes.)
EFE(1) = ((134 – 41.2 – 56.5) / 0.31) + (333 + 184 + 56 + 70 + 29 + 293)= 1082.1 Lbs.
Method 2 (Alternative Method)
If we really work at it, we can change the general formula, EFE(1), to the equivalent –
EFE(2) = (Dist / SFC) + (FTC + FTD + TDF + ALF + HF + TF) – ((DTC + DTD) / SFC)
and, since the 2nd part of the formula (in blue type) is independent of the segment distance, we can separate it out as a constant –
KFFuel = (FTC + FTD + TDF + ALF + HF + TF) – ((DTC + DTD) / SFC)
KFFuel = (333 + 184 + 56 + 70 + 29 + 293) – ((41.2 + 56.5) / 0.31)= 649.8 pounds.
Then, we can simply divide the segment distance by the specific fuel consumption (SFC), and add KFFuel to get the exact EFE fuel consumption.
EFE(2 )= (Dist / SFC) + KFFuel = (134 / 0.31) + 649.8 = 1082.1 Lbs.
Method 3 (Alternative Method)
If you’d rather work with distances, we can change the general formula, EFE(1), to –
EFE(3) = ((Dist + ((FTC + FTD + TDF + ALF + HF + TF) * SFC)) – (DTC + DTD)) / SFC
and, since the part of the formula in blue type is independent of the segment distance, we can separate it out as a constant –
KFDist = ((FTC + FTD + TDF + ALF + HF + TF) * SFC) – (DTC + DTD)
KFDist =((333 + 184 + 56 + 70 + 29 + 293) * 0.31) – (41.2 + 56.5) = 201.45 Nm
Then, we can simply add KFDist to the segment distance and divide by the specific fuel consumption (SFC) to get the exact EFE fuel consumption.
EFE(3) = (Dist + KFDist) / SFC= (134 + 201.45) / 0.31 = 1082.1 Lbs.
The above constants, KFFuel and KFDist , are valid only when the actual flight is flown at the cruise altitude with the cruise groundspeed and fuel flow, and TDF, ALF, HF, and TF used for their calculation.
Before use, your derived fuel usage data must be validated by comparing it with actual fuel usage data observed during flight operations. Do not use your derived fuel usage data if it has not been validated. Do not use your derived fuel usage data if it produces results that do not agree with observed actual fuel usage data.
To determine the minimum fuel required on board at the start of the segment, you must add the required regulatory reserve fuel to the EFE Fuel Consumption. To determine the minimum required regulatory reserve fuel, reference all regulations pertaining to your operation, including one or more of the following, as applicable:
FlightComp Systems does not recommend or advise that any operator use this information as a sole resource for any preflight planning activity.