Each plane has a slightly different fuel burn than what the manufacturer states for the model (with the actual fuel burn programmed into the flight management computer), and fuel burn also varies dramatically depending on the plane's weight. Airliners burn significant fuel on the ground, and so dispatch offices have to calculate taxi fuel. The FAA typically requires 10% of the planned fuel, but allows flag carriers to deviate from this by using Performance-Based Fuel Contingency (PBCF) to calculate fuel burn deviations based on statistical data. Block Fuel Make-Up Taxi fuel Trip fuel Contingency fuel Filed alternate fuel Reserve fuelMeanwhile, regulators also require extra reserve fuel, which is not meant to be used during normal operations. The crew decided to enter a holding pattern while diagnosing the problems, burning through their reserve fuel as they worked through the failures.