# Key Takeaways - Knowing the crosswind component is critical for ensuring a landing can be safely attempted - Since decisions about crosswind occur in flight, rules-of-thumb are appropriate # Details ## Methods for Computing ### Chart [[AFH Ch9]], [[E6B]]s, and many [[POH]]s have a circular chart for looking up the crosswind based on the wind angle. While simple, this is slower and not helpful while in flight. ### Trigonometry The most precise calculation comes from trigonometry. $ wind * sin(angle) = crosswind $ This is not very helpful while in flight.^[Plus, it's probably misleadingly precise given the rounded runway or wind angle measurements] ### Estimates at 30°, 45°, and 60° The simplest practical version requires memorizing the sine at a few key angles. | Angle | Sine | Memorize Approximate % of Crosswind | | ----- | ---- | ----------------------------------- | | 30 | 0.5 | 50% | | 45 | 0.7 | 75% | | 60 | 0.9 | 100% | ### Rule of Sixths A slightly higher resolution rule-of-thumb uses the [[Rule of Sixths]]. ![[Rule of Sixths]] ## [[True North vs Magnetic North]] [[METAR]]s and [[TAF]]s are reported in true north, while runway heads are reported in magnetic north. To find the angle between them, we convert between these different 'norths' using the local [[magnetic variation]]. > [!note] > [[ATIS]]/[[AWOS]]s are reported in magnetic north, since they need to be used in flight where we use our magnetic compass for reference. > > This leads to the memory aid: [[If It's Written It Must Be True]] # Additional Resources - [[AFH Ch9]] #concept