What an E6B Actually Computes
The E6B is a flight computer — a circular slide rule on one side, a wind-triangle plotter on the other — and it exists because flight planning is a handful of small calculations that all feed each other. This digital version keeps the same tabs: density altitude and true airspeed, the wind triangle, heading corrections, leg times, and fuel. Each one hands its result to the next, so a change in temperature ripples through to the fuel you will burn without you retyping anything.
Density altitude and true airspeed come first, because they set what the airplane can do. Field elevation and altimeter give pressure altitude, temperature turns that into density altitude, and density altitude is what converts your indicated airspeed into the true airspeed the wind triangle needs.
The Wind Triangle
Three vectors: where you want to go (true course and the speed you fly through the air), what the air is doing (wind direction and speed), and what actually happens (your track and groundspeed). Solve it and you get two numbers that matter on every leg — the wind correction angle you hold to stay on course, and the groundspeed that decides your ETA and your fuel.
Magnetic heading = true heading ± variation
Compass heading = magnetic heading ± deviation
West variation is added and east subtracted — “east is least, west is best” — and the deviation card in the airplane finishes the job. Winds aloft come referenced to true north, so pull them from a winds-aloft forecast and do the conversion once, deliberately, rather than halfway through a leg.
Time, Distance, and Fuel
Groundspeed turns distance into time, and time turns burn rate into gallons. Break the route into legs, total the times, add taxi and climb, then check the number against what the tanks hold and what you are willing to land with. 14 CFR 91.151 sets the legal floor — 30 minutes of reserve by day, 45 at night, at normal cruise — and it is a floor worth beating by a wide margin, because it assumes the flight goes as planned.
The arithmetic is easy; the inputs are where flights go wrong. A burn rate copied from a different power setting, a groundspeed that ignored a headwind, or a leg measured on the wrong chart scale all produce a confident, wrong answer. Cross-check the result against your own expectation before you trust it, and re-run it in the air when the wind is not what was forecast.
Frequently Asked Questions
What is an E6B flight computer used for?
An E6B solves the arithmetic of flight planning: density altitude and true airspeed, the wind triangle (wind correction angle and groundspeed), true-to-magnetic-to-compass heading, time and distance for each leg, fuel burn and endurance, and unit conversions. The mechanical version is a circular slide rule; this one runs the same calculations from numbers you type or from live weather.
How do you calculate true airspeed from indicated airspeed?
True airspeed grows as the air thins. The rule of thumb is to add about 2% to your calibrated airspeed per 1,000 feet of density altitude — at 8,000 ft density altitude that is roughly 16% more than the indicated number. An E6B does it exactly by setting pressure altitude against temperature, which is what the density-altitude tab above computes for you.
What is the wind correction angle?
The wind correction angle is how far you turn into the wind to make the airplane track the course you drew on the chart. It comes from the wind triangle: true course, true airspeed, and the wind vector give you a heading to fly and the groundspeed you will actually make. Crab into the wind and your track stays straight; ignore it and you drift downwind at a rate that compounds over a long leg.
How do you get from true heading to compass heading?
Apply variation, then deviation: true heading corrected for local magnetic variation gives magnetic heading, and magnetic heading corrected by the deviation card on the aircraft’s compass gives compass heading. West variation is added and east is subtracted — the "east is least, west is best" memory aid. The heading tab above runs both corrections.
Do I still need a manual E6B for the checkride?
You need to be able to do the work, and many examiners expect you to demonstrate it with a manual E6B or the equivalent math. Knowing which numbers go in and what a wrong answer looks like is the point of the exercise — a digital tool is faster in the cockpit, but it will happily return a nonsense groundspeed from a mistyped wind and never blink.
How much fuel reserve is required for a VFR flight?
Under 14 CFR 91.151, day VFR requires enough fuel to fly to the first point of intended landing plus 30 minutes at normal cruise; at night it is 45 minutes. That is a legal minimum, not a plan — most pilots hold an hour, and the fuel tab above lets you set the reserve you actually intend to land with rather than the one the regulation permits.