What an E6B flight computer does and why pilots use it

An E6B flight computer is a mechanical calculator designed to solve the math problems pilots face before and during flight. It performs four core functions: it converts between true airspeed and indicated airspeed, calculates fuel burn and flight time, converts between distance and time at a given speed, and solves wind correction problems. Pilots use it because it works without electricity, gives answers in seconds, and requires no internet connection — all critical when you are planning a flight or troubleshooting mid-air.

The device has two sides. The front is a circular slide rule with speed, distance, and time scales. The back is a wind correction grid printed on plastic, used to figure out what heading to fly when wind is pushing you sideways. Both sides solve real problems you encounter in the cockpit.

Key Takeaways

  • The front side solves speed, distance, and time problems by aligning numbers on two rotating discs and reading the answer where a hairline points.
  • The back side is a printed grid where you draw lines to find the heading you need to fly when wind will push your aircraft off course.
  • True airspeed and indicated airspeed are different because air gets thinner at altitude; the E6B converts between them using temperature and altitude.
  • Fuel burn calculations use the gallons-per-hour your engine burns and the flight time you calculated on the front side.
  • Wind correction requires you to know your desired track, wind speed, wind direction, and true airspeed — then the grid shows you what heading to fly.

Using the front side for speed, distance, and time

The front of the E6B is a circular slide rule. The outer ring shows speed in knots. The inner ring shows distance in nautical miles. A vertical hairline (or index mark) connects them. To solve any problem involving speed, distance, and time, you align two known values and read the third where the hairline points.

Say you fly at 120 knots and want to know how far you will travel in 45 minutes. Align the 120 on the speed ring with the 45-minute mark on the time scale (usually marked as a small triangle or labeled "45"). Read across the distance ring where the hairline points — you will see 90 nautical miles. The math is the same whether you are solving for distance, time, or speed; you always align two known values and read the third.

The time scale runs around the inner edge of the outer disc. It is marked in minutes and hours. Some E6B models label it clearly; others require you to count the small tick marks. If your model is unclear, check the instruction card that came with it or look up your specific model online — the layout varies slightly between manufacturers.

Converting between true airspeed and indicated airspeed

Your airspeed indicator shows indicated airspeed — the speed the pitot tube measures. But the air gets thinner as you climb, so the pitot tube reads lower than your actual speed through the air. True airspeed is what you actually fly through the air, and it matters for fuel planning and wind correction. The E6B converts between them using altitude and outside air temperature.

On the front side, find the temperature scale (usually marked in degrees Celsius and Fahrenheit) and the altitude scale. Align the outside air temperature with your altitude. Then find your indicated airspeed on the speed ring and read your true airspeed on the inner ring directly across from it. At sea level on a standard day, indicated and true airspeed are nearly the same. At 10,000 feet, true airspeed is noticeably higher — typically 15 to 20 percent faster than what your instrument shows.

If you do not know the outside air temperature, use the standard lapse rate: air temperature drops about 2 degrees Celsius for every 1,000 feet of altitude. If it is 15 degrees at sea level, estimate 5 degrees at 5,000 feet and subtract from there.

Calculating fuel burn and flight time

Once you know your true airspeed and the distance you need to fly, you can calculate how long the flight will take and how much fuel you will burn. Use the front side to find flight time first: align your true airspeed with the distance, then read the time where the hairline points. If you fly 180 nautical miles at 120 knots true airspeed, the flight takes 90 minutes.

Next, find your fuel burn rate — this is how many gallons per hour your engine burns at the power setting you plan to use. Your aircraft manual or flight school notes will tell you this number. Multiply flight time by fuel burn rate. If your engine burns 8 gallons per hour and your flight is 90 minutes (1.5 hours), you will burn 12 gallons. Add a reserve — most pilots add 45 minutes of fuel for contingency — and you know how much fuel to load.

Some E6B models have a fuel calculator on the back or a separate scale on the front. Check your model's instruction card. The math is straightforward enough to do by hand, but the E6B speeds it up and reduces arithmetic errors.

Using the back side for wind correction

The back of the E6B is a printed grid with concentric circles and radial lines. It solves the problem of wind pushing you sideways. You know where you want to go (your desired track), you know the wind speed and direction, and you know your true airspeed. The grid shows you what heading to fly so the wind pushes you back on course.

Place a small dot at the center of the grid — this is your position. Draw a line from the center in the direction of your desired track (use the compass rose printed on the grid). Mark a point on that line at a distance equal to your true airspeed, using the scale printed on the grid. From that point, draw a line in the direction the wind is coming from, and mark a distance equal to the wind speed. The line from the center to this final point is your heading — read it off the compass rose. The distance from center to final point is your ground speed (the speed you will actually move across the ground).

This sounds complicated the first time, but it becomes automatic with practice. Many flight schools teach it step by step, and YouTube videos show the motion clearly. The grid is the only way to solve wind correction by hand, and it is accurate enough for all general aviation flying.

Reading the scales and avoiding common mistakes

E6B scales are small and crowded. The most common mistake is misreading which scale you are looking at. Before you read an answer, trace your finger from the number on the outer ring, straight across the hairline, to the inner ring. Make sure you are reading the right scale — some models have multiple scales stacked together.

Another mistake is forgetting to account for the decimal point. If you align 12 with 30 minutes and read 6 on the distance scale, that is 60 nautical miles, not 6. The E6B does not show decimal points; you have to know the magnitude of your answer. If you fly 120 knots for 30 minutes, you will travel roughly 60 miles — so if the E6B shows 6, you know it means 60.

A third mistake is using indicated airspeed instead of true airspeed for wind correction. The wind correction grid requires true airspeed. If you use indicated airspeed, your heading will be wrong and wind will push you off course. Always convert to true airspeed first.

Keep your E6B clean and dry. The plastic can crack if dropped, and the scales can become hard to read if scratched. A protective case costs little and extends the life of the device significantly.

Practicing with real flight scenarios

The best way to learn the E6B is to work through flight planning problems. Start straightforward: pick a distance, a speed, and calculate time. Then add altitude and temperature and convert to true airspeed. Then add wind and use the back side. Each step builds on the last.

Many flight schools provide practice problems in their ground school materials. If you are self-teaching, create scenarios from real flights: pick an actual airport pair, look up the distance, estimate a wind direction and speed, and solve for heading and ground speed. The more you practice, the faster you become, and the more confident you are when you use it in the cockpit.

Some pilots still use the E6B even though they have GPS and electronic flight computers. It is a backup, a way to catch errors, and a skill that works when electronics fail. Learning it thoroughly is worth the time.

Frequently Asked Questions

What is the difference between true airspeed and indicated airspeed?

Indicated airspeed is what your airspeed indicator shows; it is based on how fast air flows into the pitot tube. True airspeed is your actual speed through the air. At altitude, air is thinner, so the pitot tube reads lower than your real speed. The E6B converts between them using temperature and altitude.

Can I use the E6B if I do not know the outside air temperature?

Yes. Use the standard lapse rate: air temperature drops about 2 degrees Celsius per 1,000 feet of altitude. If you know the temperature at sea level, subtract 2 degrees for every 1,000 feet you climb. This estimate is close enough for flight planning.

Do I need to use the E6B if I have a GPS?

No, but many pilots carry one as a backup. GPS can fail or lose signal. The E6B works without power and teaches you to understand the math behind flight planning. It is also required for some flight training and checkrides.

How do I know if I am reading the right scale on the E6B?

Trace your finger from the number on the outer ring straight across the hairline to the inner ring. Check that the scale label matches what you are solving for — speed, distance, time, or temperature. If your answer does not make sense (for example, flying 120 knots for 30 minutes and getting 6 instead of 60), you are likely misreading the scale or forgetting the decimal point.

What do I do if my E6B gets damaged?

If the plastic cracks or the scales become unreadable, the device is no longer reliable. E6B flight computers cost between 15 and 40 dollars new, depending on the model and brand. Keep yours in a protective case to avoid drops and scratches.