The E6B Flight Computer

A slide rule for pilots

The E6B is a circular slide rule built for flight planning. According to its Wikipedia entry, it was developed in the United States by Naval Lieutenant Philip Dalton in the late 1930s. Its name is not an acronym: it comes from the original part number for the U.S. Army Air Corps.

It has two sides:

• The calculator side, a logarithmic slide rule for time, speed and distance, fuel, true airspeed, density altitude and unit conversions.
• The wind side, a rotating transparent rose over a sliding grid, for solving the wind triangle: heading, wind correction angle and ground speed.

Almost every problem on the calculator side is the same move: line up a rate with the RATE index, then read the answer against it. The how-to guide works through each one with numbers, and the E6B simulator lets you try them.

Mechanical and electronic

Mechanical E6Bs are the aluminum or plastic wheels most students recognize. They need no batteries, cost little and make the relationships visible: set a ground speed and the whole wheel becomes a table of time against distance for that speed. You read them to about three significant figures and place the decimal point by estimate.

Electronic flight computers, such as Sporty's Electronic E6B and ASA's CX-3, put the same problems behind menus and a keypad. They are faster, remove reading error and handle unit changes for you. They need batteries, and for the knowledge test their memory must be cleared in front of the proctor.

Online calculators like this site's do the same math as both and show every step, which makes them good for learning and checking. They run on a phone or computer, though, and those are not allowed in the testing room.

What the FAA allows in the knowledge test room

The rules are in FAA Order 8080.6H, Conduct of Airman Knowledge Tests. It replaced Advisory Circular 60-11C, which the FAA cancelled in August 2025. In summary:

• applicants may use scales, straightedges, protractors, plotters, navigation computers, blank log sheets, holding-pattern entry aids and electronic or mechanical calculators directly related to the test;
• aviation-oriented calculators are allowed, including simple arithmetic calculators; instructions permanently printed on a device (formulas, conversions) are fine;
• electronic calculators must have their memory erased before and after the test, and devices that store programs or information related to the test are prohibited;
• applicants may not bring portable phones, electronic planners or any device that can record text or video into the testing area;
• the testing center has the final say on what may be used.

So bring a mechanical E6B or an electronic flight computer whose memory you can clear, and leave this website for practice.

Choosing one for training

• Ask your instructor which model the ground school uses; learning on the same wheel saves confusion.
• Check the wind side. Some compact models have a smaller grid, which is harder to read.
• For electronic models, confirm you know how to clear the memory, and carry spare batteries.
• Practice both ways. Work a problem on the wheel, check it with a calculator, and you will spot mistakes quickly.

Whichever you choose, the method is the same: estimate first, then let the computer refine the number.