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AC 150/5300-4B 6/2h/75 a. Wind coverage is that percent of time for which operations are con- sidered safe due to acceptable crosswind components. The desirable wind coverage for an airport is 95 percent,based on the total hours of weather observations. At some locations, the daily time period for weather observations is less than 24 hours; i.e., 16 hours. In any event, the data collected must be applied with an under- standing of the objective; i.e., to attain 95-percent usability. At many airports, airplane operations are almost nil after dark. Accordingly, it may be desirable to analyze the wind data on less than a 24-hour observation period. Also, at resort airports, where operations are predominantly seasonal, regard should be given to the wind data for the predominant -use period. b. Where a single runway cannot be oriented to provide 95-percent coverage, one or more additional runways will be required to raise the coverage to that value. c. The acceptable coverage value of 95 percent was selected after con- sideration of various factors influencing operations to and from airports and the economics of providing the coverage. In any air- port operation, there are periods when factors other than wind determine when a runway may be used. Low ceilings, reduced visibility, periods of runway maintenance, etc., may preclude use of a particular runway even though existing wind conditions are favorable. d. Appendix 3, Weather Data Source and Analysis, states in detail how a standard wind rose is compiled and used. Page 8 Chap 3 Par 10 •