What is Fuel on Board (FOB) used for in flight planning?

• A. The total usable fuel on the aircraft at any given time used to calculate endurance and reserves.
• B. The amount of fuel required to reach the destination from takeoff.
• C. The fuel present in the auxiliary tanks only.
• D. The fuel burned during takeoff and climb.

Answer: (A)

Fuel on Board is the total usable fuel currently on the aircraft. In flight planning, this tells you how long you can fly before needing to land, after accounting for required reserves. By dividing the current onboard fuel by the anticipated hourly burn, you obtain endurance—the true flying time available with the fuel on hand. This helps ensure there’s enough fuel for the planned trip plus contingencies and an alternate if needed. It’s the overall amount across all tanks, not just a subset, and it’s not the fuel required to reach the destination (that would be the trip fuel). It also isn’t the fuel burned during takeoff and climb; that burn reduces FOB as you fly.