FAA Aircraft Dispatcher (ADX)Flight Planning and PerformanceMedium
An aircraft is cruising with a true airspeed of 350 knots and a fuel flow of 5,000 pounds per hour. What is the aircraft's specific range in nautical miles per 1,000 pounds of fuel?
- A70 NM per 1,000 lb
- B175 NM per 1,000 lb
- C14 NM per 1,000 lb
- D50 NM per 1,000 lb
Show answer & explanationAnswer & explanation
Correct answer: A. 70 NM per 1,000 lb
Specific range = TAS ÷ fuel flow = 350 ÷ 5,000 = 0.07 NM per pound, which equals 70 NM per 1,000 pounds of fuel.
Why the other options are wrong
- B. 175 NM per 1,000 lb overstates the range by a factor of 2.5.
- C. 14 NM results from dividing fuel flow by TAS instead of TAS by fuel flow.
- D. 50 NM per 1,000 lb would require a fuel flow of 7,000 lb/hr, not 5,000.
Specific Range
Specific range measures how many nautical miles an aircraft travels per unit of fuel consumed, calculated as TAS divided by fuel flow.
- Formula: Specific range = TAS ÷ fuel flow
- Often expressed as NM per 1,000 or per pound of fuel
- Higher specific range means more efficient cruise performance
Memory trick: 'Speed over burn tells you how far you'll turn.'