Navigation Logs and Fuel Planning
Core concepts
A navigation log is a leg-by-leg table: waypoint, track, TAS, wind, HDG, GS, distance, ETE, ETA, fuel flow, fuel burn, and remaining fuel. Fuel planning must include trip fuel, contingency fuel, alternate fuel, final reserve, and taxi fuel, plus any additional fuel required by the operator. Contingency fuel is typically a percentage of trip fuel (commonly 5%) or a time-based value. Final reserve is the fuel to hold for 30 minutes at 1,500 ft above the alternate in ISA conditions (for commercial operations).
Traps
Questions often test: forgetting taxi fuel; using still-air fuel for a leg with a headwind; confusing fuel flow (kg/h) with fuel burn (kg); mixing litres and kilograms (use density ~0.72–0.80 kg/L for Jet A-1); and failing to account for contingency being based on trip fuel only, not total fuel.
Worked example / rule of thumb
Rule: fuel burn = fuel flow × ETE. Example: leg 240 NM, GS 160 kt → ETE = 1.5 h. Fuel flow 40 kg/h → burn = 60 kg. With 5% contingency on trip fuel: 3 kg. Alternate 30 NM at 150 kt = 0.2 h × 40 = 8 kg. Final reserve 30 min = 20 kg. Taxi 5 kg. Total required = 60 + 3 + 8 + 20 + 5 = 96 kg. Add at least 10% for planning uncertainty and check against aircraft maximum fuel and MTOW.