The U. S. Coast and Geodetic Survey’s sectional aeronautical chart series was introduced in 1931, and remained in print until the close of the century. Generally considered the first modern aeronautical chart, it was designed to meet the needs of newer and safer all metal passenger aircraft with increased range and speed, the emergence of a national airways infrastructure associated with Air Traffic Control Centers that promoted long range commercial flight, and the development of radio navigation that made all-weather instrument flying possible. Each sheet provides coverage for an area approximately 140 miles by 320 miles, reflecting the increased speed and range of aircraft during the 1930s.
The Survey’s sectional charts covered the continental United States in 87 sheets, each of which was thoroughly flight checked before publication. The series was projected on the Lambert conformal conic projection at a scale of 1:500,000 to facilitate chart comparison and planning. It was a major improvement over the Rand McNally Air Trails series, which varied in scale from state to state.
Two radio navigation symbols are displayed on the chart shown here, which reflected a transition period during the development of radio navigation aids. The heavy magenta lines represents the ground based four-course radio range system, which was developed by the U. S. Bureau of Standards and served as the standard navigational aid in the United States from 1928 to the 1950s. Some 400 radio range beacons ultimately comprised the nation’s civil airways system. Spaced about 90 miles apart, each beacon transmitted continuously four compass bearing that were aurally interpreted by pilots through their headphones. Pilot flew along “radio-beam airways” from beacon to beacon by one of four bearings identified by the Morse code letters N (dash-dot) or A (dot-dash) and their combinations.
The large compass rose symbols signify Very High Frequency (VHF) Omni-directional radio range stations (VOR). Beginning in the mid-1950s, radio range stations were gradually replaced by VORs, and its military version, Tactical Air Navigation or VORTAC, which transmitted very high frequency signals in all directions. A VOR were used for orientating aircraft, position fixing, and tracking. On aeronautical charts, the VOR Compass rose centered on a VHF Omni station replaced the magnetic rose.
The heavily colored notated lines and corridors represent the channels or borders of named airways within which pilots were required to fly. “Amber 7” and “Red 17,” for example, indicated low altitude named airways associated with the four-course radio range system while “V7W” noted “Victor Airways” associated with VOR.
The chart’s verso contains a legend, index map, and detailed navigation information.
This aeronautical chart series remained in print throughout the century, although it was reformatted in the late 1960s and reduced to 37 sheets printed back to back to limit the number of maps carried in the cockpit. Most other countries eventually adopted its format and scale.