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The E6B flight computer — affectionately known throughout aviation as the "whizz wheel" — is a circular logarithmic slide rule paired with a wind vector triangle slide. Invented by Philip Dalton in the 1930s, the mechanical E6B remains an essential calculation tool permitted in both CASA (CASR Part 61 PEXO) and FAA (14 CFR / Airman Knowledge Testing) pilot exams. This comprehensive guide covers every core calculation required for Private and Commercial Pilot Licences across Australia and the United States, complete with worked calculation scenarios, step-by-step procedures, and frequently asked questions.
The front face consists of two concentric logarithmic scales: the fixed outer scale (often labelled Miles or Units) and the movable inner disc (Minutes and Hours). Because the scales are logarithmic, multiplying or dividing is accomplished simply by rotating the disc so that distances subtract or add geometrically.
The key to mastering the slide rule is understanding that the numbers are dimensionless. The graduation labelled "18" can mean 1.8 gallons, 18 nautical miles, 180 knots, or 1,800 pounds. You must use mental arithmetic to establish the magnitude: if an aircraft cruises around 120 kt, flying for 30 minutes will obviously cover roughly 60 nm, not 6 nm or 600 nm.
Time, speed, and distance calculations form the foundation of visual navigation and cross-country flight planning.
Groundspeed calculation: You track between two positive visual fixes separated by 140 NM and record an elapsed time of 56 minutes. Rotate the inner disc until 56 minutes aligns directly under 140 on the outer scale. Look at the rate index (▲60): it points directly to 150 on the outer scale. Your groundspeed is 150 knots.
Estimated Time Enroute (ETE): Your planned flight leg is 210 NM and your calculated groundspeed is 135 knots. Align the rate index (▲60) with 135 on the outer scale. Follow the outer scale around to 210 NM; read 93 minutes on the inner disc, or look at the hours scale below it to read 1 hour 33 minutes.
Distance Flown: You have been cruising at 115 knots groundspeed for 38 minutes. Align ▲60 with 115 on the outer scale. Locate 38 minutes on the inner disc; read 72.8 (round to 73 NM) on the outer scale.
Fuel planning on the E6B uses the exact same rate-ratio principle as speed: rate per hour is placed at the ▲60 index, quantity is on the outer scale, and burn time is on the inner scale.
Burn rate determination: During flight test cruise, you burn 72 litres over 100 minutes (1 hour 40 minutes). Set 100 on the inner disc opposite 72 on the outer scale. Look at the ▲60 index: it points to 43.2 litres per hour.
Endurance calculation: Total usable fuel is 160 litres and your cruise burn rate is 38 L/hr. Set ▲60 to 38. Locate 160 on the outer scale; read 253 minutes (4 hours 13 minutes) on the inner time scale.
Regulatory Reserve Requirements (Critical Exam Distinction):
Aircraft performance (takeoff distance, climb gradient, service ceiling) is dictated by air density, not altimeter height.
Calculating Pressure Altitude (PA): If your altimeter is set to local QNH (aerodrome QNH), you can determine PA using standard pressure differentials. Standard sea-level pressure is 1013.25 hPa (or 29.92 inHg). Each 1 hPa difference equals approximately 30 ft (or 1,000 ft per 1.00 inHg). Formula: PA = Elevation + (1013 - QNH) x 30. Example: Elevation 1,450 ft with QNH 1003 hPa. PA = 1,450 + (1013 - 1003) x 30 = 1,450 + 300 = 1,750 ft.
Calculating Density Altitude (DA) on the E6B: Locate the cutout window labelled "PRESSURE ALTITUDE / DENSITY ALTITUDE". Rotate the disc until Outside Air Temperature (+28 °C) aligns with your Pressure Altitude (1,750 ft). Look at the Density Altitude pointer arrow: it points to 3,450 ft. Even though the aircraft is physically at 1,450 ft AMSL, its engine and wings behave as if they are at 3,450 ft.
As altitude increases, air density drops. The pitot tube senses fewer air molecules, causing Indicated Airspeed (IAS) to under-read relative to the aircraft's actual velocity through the air mass (True Airspeed).
In the window marked "AIRSPEED", align Pressure Altitude (e.g. 7,500 ft) opposite Outside Air Temperature (OAT, e.g. +5 °C).
Without moving the disc, locate your Calibrated Airspeed (CAS, e.g. 130 knots) on the inner scale. Read True Airspeed (TAS, 147 knots) directly opposite on the outer scale.
Rule of thumb check: TAS increases roughly 1.5% to 2% per 1,000 ft of altitude above sea level.
Mach Number: For high-performance aircraft, locate the Mach Index arrow (M) inside the airspeed window. Opposite your temperature, the outer scale displays the local speed of sound in knots (approx 661 kt at standard sea level ISA +15 °C).
Altimeters assume the International Standard Atmosphere (ISA: 15 °C at MSL with a lapse rate of 1.98 °C / 1,000 ft). When operating in atmospheric temperatures significantly colder than ISA, the air column is denser and compressed. The altimeter over-reads, meaning the aircraft is dangerously lower than indicated ("High to Low or Hot to Cold, Look Out Below!").
In the Altitude Correction window on the E6B, set Pressure Altitude against Outside Air Temperature. Locate your Indicated Altitude on the inner scale and read True Altitude on the outer scale. In winter mountainous terrain, failure to apply cold temperature corrections can lead to Controlled Flight Into Terrain (CFIT).
The reverse side of the E6B solves the aeronautical wind vector triangle (Track, Heading, Wind Vector, Groundspeed, True Airspeed) mechanically without trigonometry.
Step 1 (Set Wind Direction): Rotate the rotating azimuth ring until the forecast wind direction (e.g. 040° True) aligns with the True Index mark at the top.
Step 2 (Plot Wind Velocity): Slide the transparent grid until the center circle (grommet) rests on a prominent grid line (such as 100). Using a soft pencil, mark a dot straight up along the centerline corresponding to the wind velocity (e.g. 25 knots above the grommet, resting at 125).
Step 3 (Set Planned Course): Rotate the azimuth ring until your desired True Course / Planned Track (e.g. 090°) aligns with the True Index.
Step 4 (Set True Airspeed): Slide the grid vertically until your pencil dot rests on your planned True Airspeed arc (e.g. 140 knots).
Step 5 (Read Groundspeed): Read the groundspeed directly underneath the center grommet circle: 122 knots.
Step 6 (Read Wind Correction Angle): Look at your pencil dot. It lies on the divergent radial lines 7 degrees to the left of the centerline. This indicates 7° Port / Left drift. Subtract 7° from your Track (090° - 7° = 083°). Your True Heading to fly is 083°.
When flying cross-country, GPS groundspeed and heading frequently differ from flight plan forecasts due to unforecast wind shifts. You can reverse the wind triangle to calculate the exact wind aloft vector:
1. Place your actual True Course / Track flown under the True Index.
2. Slide the grid until the center grommet rests on your actual GPS Groundspeed.
3. Find the intersection of your actual Drift Angle (difference between Track and Heading flown) and your True Airspeed arc. Make a pencil dot at this intersection.
4. Rotate the azimuth ring until the pencil dot lies on the vertical centerline directly below the grommet.
5. Read the actual Wind Direction at the True Index, and count the grid units between the grommet and pencil dot to read the actual Wind Speed in knots.
Every aircraft has a Maximum Demonstrated Crosswind component published in Section 5 of the Pilot Operating Handbook (POH). Exceeding this limit during landing invites loss of directional control and runway excursion.
Example: Landing on Runway 24 (Magnetic heading 240°). ATIS reports surface wind 280° at 22 knots.
Calculate the angular difference: 280° - 240° = 40° off the runway centerline from the right.
Using the E6B crosswind grid or trigonometric scale: Crosswind = 22 x sin(40°) = 14.1 knots (Right Crosswind). Headwind = 22 x cos(40°) = 16.9 knots. If flying a Cessna 172 (15-knot demonstrated crosswind limitation), this landing is near maximum demonstrated capability and requires positive wing-low crosswind technique.
Descent planning ensures passenger comfort and avoids unstable high-speed arrivals. Standard passenger transport and IFR instrument approaches use a 3-degree descent gradient.
According to the 1-in-60 rule, a 1° slope is equal to 100 ft per nautical mile. Therefore, a 3° slope is equal to 300 ft per nautical mile.
Calculating Top of Descent: Cruising at 8,500 ft AMSL, descending to a circuit altitude of 1,500 ft. Altitude to lose = 7,000 ft. Distance required = 7,000 / 300 = 23.3 NM from the aerodrome.
Calculating Required Rate of Descent (ROD): Rule of thumb at 3° gradient: Groundspeed x 5 = Rate of descent in ft/min. At 130 knots groundspeed: 130 x 5 = 650 ft/min. On the E6B slide rule, set ▲60 to 130 kt, align 23.3 NM, and verify elapsed descent time of 10.7 minutes (7,000 ft / 10.7 min = 654 ft/min).
The 1-in-60 rule states that 1 nautical mile off track at 60 nautical miles flown equals a 1-degree track error.
Formula: Track Error Angle (TEA) = (Distance Off Track / Distance Flown) x 60.
Closing Angle (CA) = (Distance Off Track / Distance to Run) x 60.
Total Correction Angle to fly direct to destination = TEA + CA.
Worked Example: Planned leg length is 120 NM. At 40 NM flown, you fix your position 4 NM right of track. Distance to run = 80 NM. TEA = (4 / 40) x 60 = 6° Right drift. CA = (4 / 80) x 60 = 3°. Total heading alteration = 6° + 3° = 9° Left to track direct to destination.
Aeronautical charts and aircraft flight manuals mix metric and imperial units. The E6B features dedicated index arrows along the outer scales for instant zero-math conversions.
Distance conversions: Locate the Nautical Miles (NAUT), Statute Miles (STAT), and Kilometres (KM) arrows on the outer ring. Set the known distance under its respective arrow and read the equivalent distances under the other two arrows without moving the disc (e.g. 100 NM = 115 Statute Miles = 185.2 Kilometres).
Volume and Weight conversions: Set the US Gallons (US GAL), Imperial Gallons (IMP GAL), or Litres (L) index opposite the quantity. To convert fuel volume to mass, standard aviation densities apply: AVGAS 100LL is 0.72 kg/L (6.0 lbs/US gal); Jet-A1 is 0.80 kg/L (6.7 lbs/US gal). Oil is 0.90 kg/L (7.5 lbs/US gal).
An E6B flight computer is a mechanical circular slide rule and vector calculation tool developed for aviation navigation. It consists of a rotating logarithmic slide rule on the front face (for speed, time, distance, fuel burn, density altitude, and unit conversions) and a wind vector slide on the reverse face (for calculating wind correction angle and groundspeed).
For CASA exams (PEXO under CASR Part 61), candidates are permitted to use manual mechanical flight computers (such as the Dalton E6B, Jeppesen CR, or permitted navigation slide rules) and basic electronic calculators. However, digital devices with alphanumeric memory or communication capability are strictly prohibited. For FAA Airman Knowledge Tests, mechanical E6Bs and approved handheld electronic aviation computers (like the Sporty's Electronic E6B or ASA CX-3) are permitted, provided the memory is cleared before entering the testing room.
The E6B circular slide rule is dimensionless: numbers scale logarithmically by powers of ten. The graduation marked "12" can represent 1.2, 12, 120, or 1,200 depending on what you are calculating. Always perform a quick sanity check using mental arithmetic: if flying at 100 knots for 30 minutes, the distance must be around 50 nm (not 5 nm or 500 nm). Once you know the expected ballpark number, the E6B provides precision to the nearest tenth or knot.
The large solid arrow marked 60 (▲60) represents 60 minutes in an hour. It is used for all rate-per-hour calculations such as groundspeed (knots = nautical miles per hour) and fuel flow (litres or gallons per hour). The smaller arrow marked 36 (▲36) represents 3,600 seconds in an hour. It is used when converting rates into seconds, such as fuel burn per second or timing a procedure turn or holding pattern leg.
Indicated Airspeed (IAS) is measured directly by the pitot-static system and reflects dynamic air pressure. As an aircraft climbs, atmospheric density decreases. To generate the same dynamic pressure on the pitot tube, the aircraft must travel physically faster through the thinner air mass. True Airspeed (TAS) is the actual physical speed of the aircraft relative to the surrounding air. TAS increases by approximately 1.5% to 2% per 1,000 feet of altitude above sea level.
Under Australian CASA CASR Part 91 (and MOS Schedule 2), aeroplanes require a mandatory 45-minute fixed fuel reserve for both Day VFR and Night VFR. Helicopters require 20 minutes Day VFR and 30 minutes Night VFR. In addition, commercial CPL operations under Part 135 require contingency/variable reserves (typically 10%). Under US FAA 14 CFR 91.151, aeroplanes require a 30-minute reserve for Day VFR and 45 minutes for Night VFR, while rotorcraft require 20 minutes for both Day and Night VFR. In both jurisdictions, reserve fuel must be intact upon arrival at the destination or alternate.
Standard sea level pressure is 1013.25 hPa (used in Australia, Europe, and ICAO standards) which equals 29.92 inches of mercury (inHg, used in the United States). To convert inHg to hPa, multiply inHg by 33.8639 (e.g. 29.92 x 33.8639 = 1013.2 hPa). To convert hPa to inHg, divide hPa by 33.8639 (e.g. 1013 / 33.8639 = 29.92 inHg). On the E6B slide rule, place the conversion arrow or set 29.92 opposite 1013.
Yes! Aero Academic provides a fully interactive digital E6B Whizz Wheel flight computer directly in your browser. It includes a rotating circular slide rule, interactive wind vector slide, step-by-step masterclass tutorials, instant presets for common CASA and FAA problems, and targeted exam practice drills. You can access it via the Flight Computer tab in the study workstation, inside our live exam simulator, or as a standalone Chrome/Edge browser extension.
https://www.aeroacademic.com.au/guides/e6b-flight-computer-whizz-wheel-guide