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