FAA Sport Pilot Airplane (SPA)Airspace and NavigationMedium
A pilot is flying a 165 nautical mile leg. After 30 minutes of flight, GPS shows 80 nautical miles remaining to the destination. Based on the groundspeed calculated from the first 30 minutes, how much additional time is needed to complete the leg?
- A28 minutes
- B36 minutes
- C32 minutes
- D24 minutes
Show answer & explanationAnswer & explanation
Correct answer: A. 28 minutes
Distance covered in 30 minutes = 165 − 80 = 85 NM, giving a groundspeed of 85 NM ÷ 0.5 hr = 170 knots. Time for remaining 80 NM = 80/170 hr = 0.4706 hr ≈ 28 minutes.
Why the other options are wrong
- B. This significantly overestimates the remaining time.
- C. This overestimates time by using a groundspeed lower than actually calculated.
- D. This underestimates the time by using too high a groundspeed.
Groundspeed & ETE Calculation
Groundspeed is determined by dividing distance traveled by time elapsed; estimated time enroute (ETE) for remaining distance is found by dividing remaining distance by groundspeed.
- Groundspeed = distance ÷ time
- ETE = remaining distance ÷ groundspeed
- Convert hours to minutes by multiplying by 60
Memory trick: D=ST: Distance equals Speed times Time — rearrange to solve for any unknown.