How to use an E6B flight computer
An E6B is two tools sharing one disc: a wind side that solves the wind triangle, and a circular slide rule that does everything else. Work through both below, then check every answer against the free online E6B — the numbers should match.
By Renzo, CPL · Written September 2026
The wind side
Ground speed, wind correction angle and true heading. This is the half that decides whether you arrive where you intended.
1. Know which four numbers you have and which two you want
The wind side solves one triangle. You arrive with your true course (where you want the aeroplane to track over the ground), your true airspeed, and the wind — direction it is blowing FROM, in degrees true, and its speed. You leave with two answers: ground speed, and the wind correction angle that gives you the heading to fly.
Almost every mistake at this stage is a units or reference mistake rather than an arithmetic one. Winds in a forecast are true; winds from a tower are magnetic. Mix them and the answer is wrong by the local variation before you start.
2. Set the wind on the wheel
Rotate the transparent disc so the wind direction sits under the true index. Move the slide until a convenient reference line is visible, then mark a dot straight up from the centre at a distance equal to the wind speed. That dot is the wind, and it stays put for the rest of the problem.
3. Set your true course and read the triangle
Turn the disc until your true course is under the true index. Slide the card until the dot sits on the arc matching your true airspeed. Now read two things: the value under the centre grommet is your ground speed, and the number of degrees the dot sits left or right of the centre line is your wind correction angle.
Right of centre means the wind is pushing you left, so you crab right: add the angle to your true course. Left of centre means subtract. Getting the sign the wrong way round is the single most common error on the written exam, and it is worth saying out loud each time: crab into the wind.
Worked example · True course 360°, TAS 120 kt, wind from 270° at 20 kt. The wind is a pure left crosswind, so the wind correction angle comes out about 10° right — fly 010° — and ground speed stays close to 118 kt, because a crosswind costs you very little speed but a lot of heading.
Want this E6B on your phone when you are off Wi-Fi?
We are shipping Rotate E6B Flight Computer for iPhone and iPad on November 10, 2026 — the same math you just ran, working with no signal in the cockpit. You are on a desktop right now, so there is nothing to install today: leave your address and we will tell you the day it is out.
One email, once, on launch day. No newsletter, no sequence, unsubscribe never needed.
The calculator side
A circular slide rule. Once you see that speed/distance/time and fuel/flow/time are the same setting with different labels, three quarters of it stops being new.
Speed, distance and time
On the calculator side, the rate index — the large 60 marked on the inner scale — is the hinge. Put your ground speed on the outer scale against that 60, and the whole wheel becomes a table: any distance on the outer scale now reads its time in minutes on the inner scale, and vice versa.
This is why the E6B survives: one setting answers every leg of the flight, not one sum at a time.
Worked example · Ground speed 120 kt against the rate index. 30 nm on the outer scale lines up with 15 on the inner: 15 minutes. 90 nm lines up with 45. No new setting in between.
Fuel burn and endurance
Identical mechanics, different label. Put fuel flow in gallons or litres per hour against the rate index and the wheel reads fuel against time in either direction: how much you will burn in a given leg, or how long the fuel on board will last.
What the wheel will not do is decide your reserve. Legal minimums and personal minimums are a judgement, and the number it gives you is endurance to dry tanks, which is not a number you ever plan to reach.
Density altitude
Use the small window marked for airspeed and density altitude. Line the outside air temperature up against the pressure altitude, and read density altitude in the window above.
The reason to care is performance: density altitude is the altitude the aeroplane thinks it is at. On a hot day at a high field it can sit thousands of feet above the elevation on the chart, and takeoff distance grows accordingly.
Worked example · Pressure altitude 5,000 ft with an OAT of 30°C gives roughly 8,000 ft density altitude — about 3,000 ft of performance you do not have, standing on a 5,000 ft field.
Unit conversions
Fixed arrows on the outer scale mark the common aviation conversions: nautical to statute miles and kilometres, gallons to litres, pounds to kilograms. Set the value against the arrow you need and read the converted figure on the adjacent scale.
These are worth practising because exam questions bury them inside a larger problem: a question gives you litres and expects an answer in pounds, and the conversion is where the answer quietly goes wrong.
Should you learn the wheel or use an app?
Both, and in that order. Flight schools and examiners still ask students to work a wind triangle on the mechanical wheel, and the exercise teaches what the numbers mean — why a crosswind barely touches ground speed, why a headwind component is not the wind speed. Once you understand the triangle, there is no virtue in turning a disc for a number you need in the air.
Now do it under exam conditions
Wind, fuel and density-altitude problems appear on every FAA written. Practise them against real exam questions with the working shown for each answer.
See the question bank