E6B & performance

The classic flight computer - crosswind components, the wind triangle, density altitude, true airspeed, and time & fuel.

Aircraft

Sets the demonstrated crosswind, the tailwind correction and the takeoff rule of thumb - those three differ by type. Everything else on this page is type-free.

Crosswind & headwind

Today's wind resolved onto the runway you are actually using.

Crosswind

13kt

From your right. Gusts of 25 kt put 18 kt across the runway.

Headwind

13kt

Wind angle

45°from the right

Past the C172S's demonstrated crosswind (17.7 kt vs 15 kt)

The gust crosswind is stronger than anything shown during certification. Another runway, another airport or another day are all valid answers.

What "demonstrated" means

It is the strongest 90-degree component a test pilot showed during certification, printed as information - not a certificated limit, and no promise about your currency, the gust spread or a wet runway. Source: Cessna 172S POH, Section 4 p. 4-5 - "Maximum Demonstrated Crosswind Velocity: Takeoff or Landing ... 15 KNOTS"; Section 5 Figure 5-4 note: "Maximum demonstrated crosswind velocity is 15 knots (not a limitation).".

Runway

RWY 27 points 270° magnetic

Wind speed (kt)

Variable wind (VRB) - no single direction

Wind FROM (°)

METAR and TAF winds are degrees TRUE. 320°T is 315°M with your variation below.

Gust (kt)

Optional. The limit check uses the gust.

Variation (°)

Off the isogonic line on your chart. Local, not a constant.

Runway numbers are MAGNETIC. The number painted on the threshold is the runway's magnetic azimuth rounded to the nearest 10 degrees, so the real centreline can lie up to 5 degrees either side - use the exact bearing from the airport chart when the answer sits near a limit. The MAG/TRUE switch says which reference your wind arrived in - it never rewrites the number you typed, and the wind is converted at most once.

Wind triangle

Heading, ground speed and wind correction for your course.

True heading

277°T

Crab 7° right into the wind

Magnetic heading

272°M

Ground speed

98kt

WCA

7° R

True course (°T)

TAS (kt)

Wind FROM (°T)

Wind speed (kt)

Magnetic variation (°)

East is least, west is best: magnetic is the true heading less an easterly variation, plus a westerly one. Leave it blank and only the true heading is given.

Both inputs are TRUE. METAR and TAF winds are already degrees true. ATIS, tower and AWOS winds are MAGNETIC - convert one to true before entering it here, or the heading will be out by the variation. The variation above is applied only to the answer, to give you the magnetic heading to fly.

Density altitude

What the air really feels like to your wing and engine.

Density altitude

3,048ft

~37% longer ground roll at this density altitude - approx 1,311 ft here (+351 ft)

Pressure altitude

1,200ft

Field elevation (ft)

Altimeter / QNH

OAT

Sea-level figure (ft)

Runway surface

Slope

Add the 1.33 general safety factor (the UK CAA strongly encourages it)

Ground roll to plan with

1,744ft

1,311 ft x safety 1.33. Factors: UK CAA Safety Sense SS09 and SS12 (2024). Elevation and temperature are already in the density altitude, so they are not applied twice.

Enter your POH's ground roll at ISA sea level (for example, the C172S short-field figures are 960 ft ground roll / 1,633 ft over a 50 ft obstacle at 2,550 lb). The two are not interchangeable - the answer is the same measurement you put in. This is a rule of thumb scaled at 12% per 1,000 ft for the C172S's fixed-pitch propeller, not chart data: use the POH takeoff chart for a go/no-go.

True airspeed

CAS corrected to true airspeed for your density altitude.

True airspeed

108kt

+8 kt over the CAS you entered

CAS (kt)

Density altitude (ft)

Your figure above: 3,048 ft

Time & fuel

How long the leg takes, what it burns, and the least fuel to start with under your reserve rule.

Leg time

0:52h:mm

7.4 gal required at your burn, before any reserve

Fuel required

7.4gal

Distance (nm)

Ground speed (kt)

Fuel burn (gph)

Reserve rule you fly under

30 minutes at normal cruising speed (14 CFR 91.151(a)(1)). How the FAA, EASA and UK reserves compare.

Reserve burn (gph)

Blank uses the cruise burn - safe here, since this reserve burns no more.

Taxi and run-up (gal)

Blank uses the C172S POH allowance.

Usable fuel on board (gal)

Least fuel to start with

13.0gal

7.4 trip + 4.3 reserve + 1.3 taxi. Wind and forecast weather go into the trip figure (91.151(a)).

Demonstrated crosswind by aircraft

The figure the crosswind card measures against, for each aircraft in the picker. It is the strongest 90-degree component a test pilot showed during certification, printed as information - not a limit, and not a promise about your currency, the gust spread or a wet runway. The C172S handbook says so in as many words: “(not a limitation)”.

Aircraft	Demonstrated	Where the figure comes from
Cessna 172S Skyhawk SP	15 kt	Cessna 172S POH, Section 4 p. 4-5 - "Maximum Demonstrated Crosswind Velocity: Takeoff or Landing ... 15 KNOTS"; Section 5 Figure 5-4 note: "Maximum demonstrated crosswind velocity is 15 knots (not a limitation)."
Cessna 172N Skyhawk	15 kt	Cessna 1978 Model 172N POH, Section 4 p. 4-3 - "Maximum Demonstrated Crosswind Velocity: Takeoff or Landing . . . 15 KNOTS"; Section 1 p. 1-7: "The value shown is not considered to be limiting."
Cessna 152	12 kt	Cessna 152 POH (1978), Section 4 - "Maximum Demonstrated Crosswind Velocity ... 12 knots"
Piper PA-28-161 Warrior II (2,440 lb)	17 kt	Piper PA-28-161 Warrior II POH, Report VB-1180 (13 Aug 1982), Section 4 - "(f) Maximum Demonstrated Crosswind Velocity 17 KTS"
Piper PA-28-181 Archer II / III	17 kt	Piper PA-28-181 Cherokee Archer II POH, Report VB-790, Section 4 - "(f) Maximum Demonstrated Crosswind Velocity 17 KTS"
Diamond DA 40 (standard tank)	20 kt	Diamond DA 40 AFM, Doc. No. 6.01.01-E Rev 7, Section 5.3.5 Wind Components, p. 5-9 (Rev 10: p. 5-10) - "Max. demonstrated crosswind component: 20 kts" (a spec sheet quoting 25 kt is not the AFM)