The 20-minute CNAF fuel requirement is based on maximum endurance airspeed at an altitude of what?

The 20-minute CNAF fuel requirement is based on maximum endurance airspeed at an altitude of what?

• A. 5000 feet
• B. 10000 feet
• C. 15000 feet
• D. 20000 feet

Answer: (B)

Endurance is about how long you can stay aloft on a given amount of fuel, so the speed you fly that minimizes fuel burn per hour—the maximum endurance airspeed—allows the longest time in the air for the fuel you carry. For planning a 20-minute fuel reserve, the calculation uses that speed. The CNAF standard uses an altitude of ten thousand feet for this endurance reference because fuel burn and lift characteristics change with density altitude, so the speed that gives maximum endurance varies with altitude. Ten thousand feet is the published reference point where the endurance data are defined, providing a consistent basis for the 20-minute fuel calculation. Using a different altitude would yield a different endurance speed, which is why this specific altitude is chosen.

Endurance is about how long you can stay aloft on a given amount of fuel, so the speed you fly that minimizes fuel burn per hour—the maximum endurance airspeed—allows the longest time in the air for the fuel you carry. For planning a 20-minute fuel reserve, the calculation uses that speed. The CNAF standard uses an altitude of ten thousand feet for this endurance reference because fuel burn and lift characteristics change with density altitude, so the speed that gives maximum endurance varies with altitude. Ten thousand feet is the published reference point where the endurance data are defined, providing a consistent basis for the 20-minute fuel calculation. Using a different altitude would yield a different endurance speed, which is why this specific altitude is chosen.