Why must planned flights include fuel reserves and an alternate airport, and how is endurance calculated?

• A. Reserves cover contingencies only; endurance = total fuel divided by power; range = TAS × endurance
• B. Reserves cover only weather; endurance and range are independent of wind
• C. Reserves cover contingencies and diversions; endurance = usable fuel / consumption rate; range ≈ TAS × endurance
• D. Reserves are optional; endurance calculation uses flight time only

Answer: (C)

Fuel planning must include reserves and an alternate airport so you’re prepared for anything that can go wrong on the flight. Reserves exist not only for contingencies but also to cover the possibility of diversions to another airport if the destination becomes unavailable due to weather, air traffic, or other factors. An alternate airport is your fallback plan if you can’t land at your intended destination.

Endurance tells you how long you can stay aloft with the usable fuel on board at your current burn rate. It is calculated by dividing usable fuel by the fuel consumption rate (fuel flow). Range is then estimated as roughly true airspeed times endurance, assuming fairly constant speed and that wind effects are considered separately if needed.

So the correct idea is that reserves cover contingencies and diversions, endurance equals usable fuel divided by consumption rate, and range is approximately TAS multiplied by endurance.