geoprimsField-grade geospatial math

VFR preflight

From the latest METAR to pressure altitude, density altitude, and the crosswind on your runway.

For pilots · 4 steps · each opens with the values filled in

Planning and education aid. Not for primary navigation. The values here are an example; use your own. Full disclaimer

  1. Step 1

    METAR decoder

    Read the weather: wind, temperature, dew point, and altimeter setting.

    You should see KDEN is VFR with wind 300° true at 15 kt, gusting 25 kt and visibility 10 SM. Get a current official briefing before flight.

    Open with these values

  2. Step 2

    Pressure altitude

    Field elevation and the METAR's altimeter setting give pressure altitude.

    Carries altimeter setting from step 1.

    You should see Pressure altitude is 5,546 ft. The 1,000 ft per inch rule gives 5,554 ft, off by 8 ft.

    Open with these values

  3. Step 3

    Density altitude

    Add the temperature and dew point: the altitude the airplane will perform at.

    Carries altimeter setting from step 1, outside air temperature from step 1, dew point from step 1.

    You should see Density altitude is 8,623 ft, about 3,200 ft higher than the field. Expect a longer takeoff roll and weaker climb.

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  4. Step 4

    Runway wind components

    Split the wind on runway 25. A METAR wind is true and runway numbers are magnetic, so the variation is applied.

    Carries wind direction from step 1, wind speed from step 1, gust from step 1.

    You should see 10 kt crosswind from the right and 11.1 kt headwind on runway 25, 16.7 kt crosswind in gusts.

    Open with these values