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6/24/75 AC 150/5300-4B Appendix 3 g. Make several orientations to either side of the original trial heading to assure that the best possible coverage and orientation have been determined. h. When determining the total wind coverage, it is usually easier to total the percent of wind occurrences which lie outside the tem- plate and subtract this total from 100 percent. This is especially true when determining the total coverage for a complex of two or more runways on a single airport. i. Runways are designated by their magnetic azimuth measured from magnetic north to the nearest 10 degrees. For example, a runway which has magnetic azimuths of 30 and 210 degrees is designated as Runway 3-21. Wind data are gathered and reported with true north as a reference. The difference between magnetic and true azimuth is equal to magnetic variation and can be obtained from aeronautical charts. When determining magnetic azimuths, easterly variation is subtracted from the true azimuth and westerly variation is added to the true azimuth. The runway orientation resulting from the wind rose analysis should be changed from true to magnetic azimuths in accordance with the above and as shown schematically in Figure 4. j• NOAA FUNCTIONS AND SERVICES. The National Oceanic and Atmospheric Administration (NOAA) of the Department of Commerce takes such Meteorological Observations as may be necessary to establish and record the climatic conditions of the United States. To do this, the Weather Bureau, a major line component of NOAA, operates a network of weather_ observing stations and records the data. The Environmental Data Service, another major line component of NOAA, services the records collected by the Weather Bureau and by other agencies such as the FAA and the military establishments. a. The National Weather Records Center (NWRC) of the Environmental Data Service, located at Asheville, North Carolina, is the collec- tion center and repository of weather records for nearly 13,000 locations in the United States and possessions and for numerous military posts throughout the world. These data, many of which are on punched cards or magnetic tape, can be made available or summarized if required. This service center can be helpful in airport planning and design to determine the availability of weather data for any location and to provide a compilation of that information in a usable format. Hourly wind observations are on record at the Center covering a period of 3 or more years for some 300 airport locations within the United States, of which 95 percent have 5 or more years of recorded observations. Par 2 Page 3