The fuel fraction during a loiter phase of flight, often referred to as “FFL” (Fuel for Loiter) or “Loiter Fuel Fraction,” represents the proportion of an aircraft’s total fuel consumption that is typically consumed during a loitering or holding pattern phase. Loitering occurs when an aircraft circles or remains in a holding pattern before proceeding to its destination or performing a specific task.
The formula for calculating the Loiter Fuel Fraction () can be expressed as:
    
- “Fuel Burned during Loiter” is the amount of fuel consumed during the loiter phase of the flight, typically measured in kilograms or pounds.
- “Total Fuel Onboard” is the total amount of fuel carried by the aircraft at the start of the flight, typically measured in kilograms or pounds.