Endurance time is the longest time the aircraft could be expected to stay airborne under planned conditions, assuming any alternate is used, all reserves are burnt, and including the extra cruise time any remaining fuel would give you.

To compute the endurance time Command Flight Planner estimates the amount of time and fuel required, at relevant consumption rates, for each of these stages of flight:

• Climb, cruise, and descent
• Fuel required for planned holds or delays
• Any fuel required to reach a specified alternate airfield from the primary destination
• Fuel required for variable reserve
• Fuel required for fixed reserve time
• Fuel required for taxi

The total of all the fuel quantities above is subtracted from the total fuel on board to give a fuel margin.  The fuel margin is converted to a potential flight time at the cruise rate.

The airborne endurance time is computed by adding all the time periods computed above excluding taxi (which is spent on the ground) and the additional time that the fuel margin supplies.  At the end of this time airborne one would expect complete fuel exhaustion.

The process above is performed for each stage of the flight plan.  The figures can be seen on the Fuel Management panel and some of the printed output of the Command Flight Planner.