FAA Aircraft Dispatcher (ADX)Flight Planning and PerformanceMedium
A dispatcher is calculating the Point of No Return (PNR) for an overwater flight with a safe fuel endurance of 5.0 hours. The ground speed proceeding outbound is 280 knots, and the ground speed returning to the departure airport is 320 knots. What is the flight time from departure to the PNR?
- A3:00
- B2:20
- C2:40
- D2:00
Show answer & explanationAnswer & explanation
Correct answer: C. 2:40
PNR distance = (Endurance x GSout x GSback) / (GSout + GSback) = (5 x 280 x 320)/(280+320) = 448,000/600 = 746.7 NM. Time to PNR = distance/GSout = 746.7/280 = 2.667 hr, which is 2 hours 40 minutes.
Why the other options are wrong
- A. Overestimates; would exceed available fuel endurance if used as PNR time.
- B. Close but does not match the correct fraction of endurance used.
- D. Too low; underestimates the safe endurance calculation.
Point of No Return (PNR)
The farthest point an aircraft can fly and still have enough fuel to return safely to the departure airport, based on fuel endurance and ground speeds in each direction.
- PNR distance = (Endurance x GSout x GSback)/(GSout+GSback)
- Time to PNR = PNR distance / GSout
- Different from Equal Time Point, which does not depend on fuel endurance
- Critical for overwater/remote area dispatch planning
Memory trick: PNR: 'Past here, turning back costs more fuel than you have'