Elrey B. Jeppesen, a United Airlines pilot flying the treacherous Rocky mountain routes out of Cheyenne and then Denver in the 1930s developed specialized instrument flight maps designed specifically for radio navigation. Jeppesen began by jotting down navigation information and making sketch maps of approaches into western airports. On his days off, he measured and mapped the obstacles along these routes in a little black book that he constantly carried with him. After selling copies of his sketch maps to other pilots for several years, Jeppesen self-published his first Airway Manual in 1934. From this small beginning, the Jeppesen Company (now Jeppesen A Boeing Company) grew to dominate the commercial aeronautical chart industry. Today about 80 percent of the world’s commercial pilots are guided by “Jepps” as pilots have dubbed them.
Jeppesen introduced low and high altitude enroute charts following the division of air traffic into two categories by the Federal Aviation Administration in 1964, thus creating a three-dimensional airspace that continues in effect. Flights below 18,000 feet mean sea level are controlled by visual flight rules (VFR) and flights above, designed for Jet airways, are controlled by instrument flight rules (IFR). Since this action, all aeronautical charts have been prepared for either VFR, such as the U. S. Coast and Geodetic Survey’s 1:500,000 sectionals charts (See Caption 3) or IFR, such as Jepco’s Avigation Low Altitude Enroute Chart, a Jeppesen product displayed here.
Jepco’s Avigation Low Altitude Enroute Chart covers the controlled airspace from 14,500-17,999 feet mean sea level. Thirty-two charts on 16 sheets cover the United States with varying scales to compensate for unequal distribution of population and aircraft facilities. The Lambert Conformal Conic Projection is used since any straight line drawn on the chart represents a great circle route, the shortest distance between two points on the earth’s surface. To keep air navigation information current, each chart is revised on a 28-day cycle.
The depiction of navigation aids on IFR charts is similar to VFR charts, but the charts themselves differ considerably. All visual ground reference points such as roads, railroads and topography have been removed from IFR charts, replaced by a system of compass roses and airways that has been characterized as “highways in the sky.” The large compass roses with triangles represent VOR Omni facility ground stations while the single line extending from the 360° radial indicates magnetic north. A VOR’s name, radio frequency, three-letter identifier and Morse code identifier are shown in an inset box adjacent to the VOR compass rose. VOR’s are linked by designated airways that are color-coded blue for low altitude Victor airways and light green for high altitude Jet airways.
Since 1947 the International Civil Aviation Organization has promoted international standards for air navigation symbols so that U. S. and foreign pilots can use one another’s charts without having to learn new symbols or abbreviations.
The quaint term “Avigation,” which is found in the map title, was coined by the Jeppesen Company in the 1930s to distinguish between “air” navigation and “maritime” navigation.