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CFI Brief: Basic Planning Calculations

It is a pilot’s responsibility prior to every flight to calculate time, speed, distance, and fuel required for that particular flight. As a pilot, you will have access to onboard systems, and tools like the CX-2 Flight Computer or E6-B that can assist in these types of calculations (check out our video tutorials on how to use your CX-2 and E6-B). But it can also be beneficial to understand the math behind these calculations—comparable to learning to read a round-dial clock before jumping right to a digital readout. Understanding the math provides a perspective you wouldn’t otherwise get by simply punching in numbers. This perspective will serve your gut instinct and help you sniff out potential problems with a “this doesn’t seem right” viewpoint. Below we will explore three simple calculations you will use regularly to determine time, distance, and ground speed.

TIME
To determine time you need two pieces of information: distance (in nautical miles) and ground speed (in knots).

Distance / Ground Speed = Time 

How long will it take you to fly a distance of 190 NM at a ground speed of 135 knots?

190/135 = 1.4 hours

To convert the .4 to minutes you need to multiply by 60.

0.4 x 60 = 24 minutes

Your answer is 1 hour and 24 minutes.

DISTANCE
This next calculation is used to determine distance flown in a given time.

Ground Speed (in knots) X Time (in hours) = Distance (in nautical miles)

How far will the aircraft fly in 1 hour and 30 minutes at a ground speed of 120 knots? The first step is to convert the 30 minutes into equivalant hours, instead of multiplying by 60 like we did above, here we will divide by 60 (30/60=0.5).

120 X 1.5 = 180 NM

GROUND SPEED
Lastly, to find ground speed we need to know distance and time.

Distance (in nautical miles)/ Time (in hours) = Ground Speed (in knots)

What is our average ground speed if we travel 250 NM in 2 hours ?

250 / 2 = 125 knots

Here are a few to try on your own.

Problem: What it the approximate time en route for a 60 NM leg with a ground speed of 110?

Problem: How far has the aircraft traveled in 1 hour 24 minutes at a ground speed of 140 knots?

Problem: What is your ground speed if you have covered 200 NM in 1 hour 45 minutes?  

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