What an E6B Flight Computer Does and How to Hold It

An E6B flight computer is a circular slide rule designed to solve the math problems pilots face before and during flight. It calculates ground speed, heading corrections, fuel burn, time to destination, and altitude conversions without needing a calculator or internet. The device has two sides: a circular slide rule on one side and a wind triangle solver on the back.

Hold the E6B with the numbered outer ring facing you. Your thumb and forefinger should grip the metal grommet (the center hole) loosely enough to spin the inner wheel freely. The device should rotate smoothly without binding. If it sticks, the wheel may be bent or the grommet may need cleaning. Most E6Bs are about 5 inches in diameter and fit in a flight bag or shirt pocket.

The front face has three main parts: the outer fixed ring with numbers and labels, the inner rotating wheel with scales, and a small window or cursor line that helps you read values where two scales meet. Learn where each scale lives before you try a calculation—the layout is the same on every E6B, whether you own a Jeppesen, ASA, or Sporty's model.

Key Takeaways

  • The E6B solves ground speed, true airspeed, heading, fuel burn, and time calculations by aligning two scales and reading the answer at a marked index or cursor line.
  • The front side handles speed and distance math; the back side (wind triangle) corrects your heading when wind is pushing you off course.
  • Every calculation starts by finding one known value on a scale, rotating the wheel to align it with a second scale, then reading the answer at a fixed index or cursor.
  • The most common mistake is forgetting to convert units (knots to statute miles, for example) before you start, which makes the answer wrong by a factor of 1.15.
  • Practice one calculation type at a time on the ground with a flight instructor or tutorial video before you use the E6B in the cockpit.

Finding Ground Speed When You Know Wind Direction and Strength

Ground speed is how fast you are moving over the ground. It is different from your airspeed (how fast the plane moves through the air) because wind pushes you forward or slows you down. The E6B's back side solves this problem using the wind triangle method.

On the back of the E6B, you will see a grid with a center point and concentric circles. The center point is your aircraft. The circles represent speed in knots (usually marked every 10 or 20 knots). A straight line runs down the middle—this is the 0-degree line, your intended direction of travel.

To find ground speed: First, mark a point on the grid that represents the wind. If the wind is 15 knots from 090 degrees and you are flying toward 180 degrees, you measure 15 knots along the 090-degree line from the center. Make a small pencil mark or use a dot of tape. Next, place your true airspeed (the speed your plane flies through still air) as a radius from that wind point. If your true airspeed is 100 knots, set a compass or use the scale on the E6B's edge to mark a circle 100 knots wide around the wind point. Where that circle crosses your intended track (the 180-degree line in this example) is your ground speed. Read it from the center point outward along your track line.

This method works for any wind direction and speed, but it requires a pencil, paper, and a few minutes. Many pilots use it during flight planning on the ground rather than in the cockpit during flight.

Calculating True Airspeed from Indicated Airspeed and Altitude

Your airspeed indicator shows indicated airspeed (IAS)—the speed the pitot tube measures. But at altitude, the air is thinner, so your plane actually moves faster through the air than the gauge shows. True airspeed (TAS) is the real speed, and you need it to calculate ground speed and fuel burn.

On the front of the E6B, find the outer ring labeled "TAS" or "TRUE AIRSPEED." Locate your indicated airspeed on the inner rotating wheel. Rotate the wheel until your IAS aligns with the temperature at your altitude on the outer ring. For example, if you are flying at 5,000 feet where the temperature is 5 degrees Celsius, and your IAS is 100 knots, rotate the wheel until 100 on the inner scale lines up with 5 degrees on the outer scale. Now look straight up at the index line or window at the top of the E6B. The number you see there is your true airspeed—in this case, roughly 110 knots.

Temperature matters because cold air is denser than warm air. On a cold day at the same altitude, your true airspeed will be lower than on a warm day. Always use the outside air temperature (OAT) from your weather briefing, not the temperature at sea level. If you do not know the temperature aloft, subtract 2 degrees Celsius for every 1,000 feet of altitude above sea level as a rough estimate.

Computing Time and Distance Using the Speed Scale

The front of the E6B also solves the classic problem: if you are flying 120 knots and need to cover 180 nautical miles, how long will it take? The answer is 90 minutes, and the E6B finds it in seconds.

On the outer ring, find the number 60 (representing 60 minutes in an hour). Rotate the inner wheel until your ground speed (120 knots in this example) lines up with the 60. Now look at the outer ring and find your distance (180 nautical miles). Look straight down at the inner wheel below it. The number you see is your time in minutes—90 minutes, or 1 hour and 30 minutes.

The same method works backward. If you know you have 45 minutes of fuel and you are flying at 100 knots, how far can you go? Align 100 on the inner wheel with 60 on the outer ring. Find 45 on the outer ring and read the distance below it on the inner wheel. The answer is 75 nautical miles. This calculation is critical for fuel planning and knowing your range.

A common mistake is mixing units. Make sure your ground speed is in knots and your distance is in nautical miles. If your chart shows statute miles instead, convert first by multiplying by 0.87 (or divide nautical miles by 1.15 to get statute miles). Using the wrong units will make your answer wrong by about 15 percent.

Correcting Your Heading When Wind Pushes You Off Course

Wind does not blow straight down your intended track. If you fly toward 180 degrees but the wind is from 090 degrees, the wind pushes you to the right (south). To stay on course, you must point the plane slightly into the wind—this is called a wind correction angle.

The wind triangle on the back of the E6B solves this. You already marked the wind point and your true airspeed circle in the earlier section. Now draw a line from the center point (your aircraft) to where your airspeed circle crosses your intended track. The angle between your intended track and this line is your wind correction angle. If the wind pushes you right, you turn left by this angle to stay on course.

For example: You want to fly 180 degrees. Wind is 15 knots from 090 degrees. Your true airspeed is 100 knots. Mark the wind point 15 knots along the 090-degree line. Draw a circle 100 knots wide around that point. The circle crosses the 180-degree line at a point that is not directly below the center. Draw a line from the center to that crossing point. If that line points to 175 degrees, your wind correction angle is 5 degrees to the left. You fly a heading of 175 degrees to track 180 degrees over the ground.

This is why the wind triangle method takes time and pencil work. Many pilots use it during preflight planning and write the answer on their flight plan. In the cockpit, you steer the heading the plan says and watch the GPS or landmarks to confirm you are on track.

Converting Between Nautical Miles, Statute Miles, and Kilometers

Charts, weather reports, and regulations use different distance units. Nautical miles appear on aeronautical charts. Statute miles appear on road maps and some older charts. Kilometers appear on some international charts and weather reports. The E6B has a conversion scale to switch between them without math.

On the front of the E6B, look for the outer ring labeled with distance units—usually "NAUTICAL MILES," "STATUTE MILES," and "KILOMETERS" at different points around the circle. Find your known distance on one scale. Rotate the wheel or use the cursor line to read the same point on a different scale. For example, if a chart shows 50 nautical miles, find 50 on the nautical miles scale. Read straight across to the statute miles scale and you see 57.5 statute miles. Read to the kilometers scale and you see 92.6 kilometers.

The conversion factors are fixed: 1 nautical mile equals 1.15 statute miles, and 1 nautical mile equals 1.85 kilometers. The E6B's scales are built with these ratios, so you do not have to remember or calculate them. This is one of the fastest and most reliable uses of the E6B because it is purely mechanical—no wind, temperature, or altitude to account for.

Solving Fuel Burn and Range Problems

Your aircraft burns fuel at a known rate—for example, 8 gallons per hour. If you have 40 gallons of usable fuel, how long can you fly? The E6B solves this the same way it solves time and distance.

On the front, align your fuel burn rate (8 gallons per hour) with 60 on the outer ring. Find your total fuel (40 gallons) on the outer ring. Read the time below it on the inner wheel—5 hours. Now multiply that time by your ground speed to find your range. If your ground speed is 120 knots, 5 hours times 120 knots equals 600 nautical miles of range.

Always use usable fuel, not total fuel. Your fuel gauges show total capacity, but the last few gallons in the tank are usually not reachable by the fuel pump. Check your aircraft's manual for usable fuel. Also, subtract a reserve—most regulations require 30 minutes of fuel remaining at your destination, and many pilots add another 30 minutes as a safety margin. If you can fly 5 hours total, subtract 1 hour for reserve, leaving 4 hours of planning range.

Fuel burn changes with altitude, engine power, and temperature. The number on your E6B is only as good as the fuel burn figure you put in. If you have never flown your aircraft before, use the manufacturer's estimate and watch your actual burn during the flight. After a few hours, you will know your real numbers and can plan more accurately.

Common Mistakes and How to Avoid Them

The most frequent error is forgetting to convert units before starting a calculation. If you use statute miles when the scale expects nautical miles, your answer will be off by 15 percent. Always check the label on the scale you are using and convert your input numbers first if needed.

A second mistake is misreading the scales. The E6B's numbers are small, and the inner and outer rings can be confusing. Use a straightedge or the cursor line that comes with many E6Bs. Line it up vertically or horizontally (depending on which scales you are reading) and follow it carefully from one scale to the other. A small error in reading can compound into a big error in the answer.

Pilots also forget to account for wind when calculating time and distance. If you use ground speed (which includes wind) for one part of the problem and true airspeed (which does not) for another, the answer will be wrong. Write down which speed you are using before you start, and stick with it throughout the calculation.

Finally, many pilots trust the E6B without checking the answer for reasonableness. If the E6B says you can fly 600 nautical miles on 40 gallons of fuel, but your aircraft manual says the range is 400 nautical miles, something is wrong. Double-check your input numbers and your reading of the scales. The E6B is a tool—it does what you tell it to do, but it cannot tell you if you fed it bad information.

Frequently Asked Questions

Do I need an E6B if I have a GPS and a calculator?

No, but many flight instructors require students to learn the E6B because it teaches the math behind navigation and does not depend on batteries or satellites. A GPS can fail, and a calculator is useless if you do not understand what number to calculate. The E6B is a backup and a learning tool. Many experienced pilots carry one anyway because it is fast and reliable for preflight planning.

Which side of the E6B do I use first?

Start with the front side for speed, distance, time, and fuel calculations. Use the back side (wind triangle) only after you know your true airspeed and need to correct for wind. Most flights begin with front-side math during preflight planning, then move to the back side if wind is significant.

What if the inner wheel is hard to turn?

The wheel may be dirty, bent, or the grommet may be too tight. Try cleaning around the center hole with a soft brush. If it still binds, the E6B may be damaged and should be replaced. A stuck wheel makes the E6B useless because you cannot align the scales accurately.

Can I use an E6B on a tablet or phone instead of the physical version?

Yes, many apps replicate the E6B's functions and some add features like wind triangle graphics. However, apps require power and a screen you can see in bright sunlight. A physical E6B never runs out of battery and works in any light. Many pilots use both—an app for detailed planning at home and a physical E6B for the cockpit.

How do I know if I am reading the E6B correctly?

Check your answer against the real world. If the E6B says you will arrive in 2 hours but you know the distance is short, something is wrong. Practice on the ground with known numbers first. For example, calculate the time to fly 60 nautical miles at 120 knots—the answer should be 30 minutes. If you get something else, you are reading the scales wrong.