There are 2 ways of doing this. Either calculate Specific Fuel
Consumption (SFC), which is given by Fuel Flow/ground speed (SFC = Kgs of fuel used per ground nm; therefore, the lower the
figure the better), or calculate the total fuel required for this 440nm
navigation leg…I’ll use SFC….
Now, they have been awkward…..the question refers to FLs
50/100/180 and the cruise data is given at FLs 40/80/120/160/200. Also, the
question gives fuel flow as Litres/hour rather than kg/hr but we can still use
it to find a measure of efficiency – Litres of fuel used per ground nm.
We need to interpolate and expand ANNEX A to find the data at
Flight Levels 50/100/180 and then divide fuel flow by groundspeed to find the
lowest SFC.
FL |
40 |
50 |
80 |
100 |
120 |
160 |
180 |
200 |
TAS |
190 |
192 |
198 |
201 |
204 |
212 |
216 |
220 |
Wind |
-30 |
-50 |
-70 |
|||||
GS |
162 |
151 |
146 |
|||||
L/hr |
210 |
208 |
202 |
192 |
182 |
170 |
163 |
156 |
SFC |
1.283 |
1.271 |
1.116 |
The best range performance is at FL180 where the SFC is 1.116
L/NGM