Cruise Flight Planning with Upper Winds and Fuel Reserve
You are planning a 900 NM leg at FL300. Forecast wind at FL300 is 250°/80 kt, temperature −45 °C. The aircraft cruises at TAS 450 kt. Planned track is 090°M, variation 5°E. Fuel flow is 2,400 kg/h at cruise. Contingency fuel is 5% of trip fuel, alternate fuel is 1,200 kg, final reserve is 30 minutes holding at 1,800 kg/h. Take-off mass is limited to 64,000 kg, and the zero-fuel mass is 52,000 kg.
1. Compute the cruise groundspeed, trip time, and trip fuel.
Read the worked answer
Wind 250/80, track 090. The wind is 20° off the nose to the left (250 vs 090: wind from 250 means it blows toward 070, so it is a headwind component). Headwind ≈ 80 cos20° ≈ 75 kt; crosswind ≈ 80 sin20° ≈ 27 kt. WCA ≈ arcsin(27/450) ≈ 3.4°, so heading ≈ 093.4°M (086.6°M true? no: track 090, wind from left, so heading must be into wind: 090 + 3.4 = 093.4°M). Groundspeed ≈ 450 − 75 ≈ 375 kt. Trip time = 900/375 = 2.4 h = 2 h 24 min. Trip fuel = 2,400 × 2.4 = 5,760 kg.
2. Determine the total fuel required and whether the take-off mass limit is respected.
Read the worked answer
Contingency 5% of trip fuel = 288 kg. Alternate 1,200 kg. Final reserve 30 min at 1,800 kg/h = 900 kg. Total fuel = 5,760 + 288 + 1,200 + 900 = 8,148 kg. Take-off mass = zero-fuel mass 52,000 + 8,148 = 60,148 kg, below the 64,000 kg limit, so the flight is legal. If the wind were 20° stronger or the temperature higher, the trip fuel would rise; check the margin: 64,000 − 60,148 = 3,852 kg spare, enough for about 1.6 h extra cruise. Note that the −45 °C temperature at FL300 is close to ISA (−44.5 °C), so no significant temperature correction to TAS is needed.