Flight Planning and Navigation Computations
The Flight Plan Leg
For each leg you need distance, true track, wind, TAS, groundspeed, time and fuel. Fuel = fuel flow × time; time = distance/groundspeed. Safe endurance is fuel available divided by hourly consumption, and the reserve must be respected.
Building the Plan
Compute the wind triangle for each leg, derive groundspeed, then time = distance/GS. Sum leg times for ETA, adding departure time in UTC. Fuel required = (trip fuel + reserve + contingency + taxi) and must not exceed usable fuel; check mass and balance limits.
Point of No Return and Critical Point
Equal time point (ETP) is where time to return equals time to continue; it depends on wind and fuel. The point of no return is where fuel remaining just allows return to base.
Traps
Units: knots with nautical miles and hours; fuel flow in kg/h or lb/h. Watch for wind given in magnetic or true, and for ETA crossing midnight or the date line. Always keep the reserve intact.
Worked Example
Leg 240 nm, GS 120 kt → 2.0 h. Fuel flow 40 kg/h → 80 kg trip fuel. Add 45 min reserve (30 kg) and 10% contingency (8 kg): total 118 kg.
Rule of Thumb
Time (min) = distance (nm) / groundspeed (kt) × 60. At 120 kt, 2 nm per minute; at 90 kt, 1.5 nm per minute.