Printed Navigation Aids

In the earliest days of flying, pilots had no reliable way of finding their way. They relied on visual aids—what they could see from their cockpit, on compasses that were often undependable, and maps that were designed for automobile travel. As a result, many got lost and ended up miles from their intended destination. They also had no way of knowing when they would come across mountains or other obstacles until they were almost upon them and no way of knowing the location of landing fields.

In May 1918, the U.S. Post Office Department launched scheduled airmail service. The first pilot who departed from the polo grounds in Washington, D.C., with the mail had only verbal advice to follow—he was told to follow the railroad tracks north from the city. Not surprisingly, he got lost. As the system of airmail routes expanded, pilots began keeping notebooks they could fit in their pockets or hold in their hand. They shared notes with each other about official landing fields, emergency fields, and ways to find landmarks between towns in the daytime.

Administrators quickly realized that an official system was needed for navigation. The Post Office began collecting the pilots' notes and on February 20, 1921, the second Assistant Postmaster General Otto Praeger published the first federal, printed guide to navigation that covered the entire 2,629 miles (4,231 kilometers) from New York to San Francisco. These United States Air Mail Service Pilot Directions included landmarks within five miles (eight kilometers) on either side of the line of flight and showed the magnetic compass course between points and locations of airmail facilities with services such as fuel, oil, and repair.

From the 1930s, the Pilot Directions also described painted landmarks, called airmarks, that could be seen only from the air. These airmarks were painted on the roofs of theaters, hotels, railroad stations and even hillsides beginning around World War I to identify the latitude, longitude, and name of the town or to steer pilots toward the nearest airport with a huge arrow. Sometimes, signs advertised a good restaurant for pilots. For example, pilots were told that the airfield near Omaha, Nebraska, could be found by flying toward a large oval racetrack, then searching for a hangar with a white circle and cross painted on the roof. If pilots could not find the airfield, the racetrack was described as a good emergency landing site. A federal air-marking program began in the 1930s and lasted into the 1970s. Today, the 99s (the women's pilots group) still paints airmarks around the country.

The Pilot Directions also printed the earliest landing aids—guidelines for the best approach to a field while descending. Airmail pilots landing at Omaha, for example, should “follow a road five miles from the Missouri River, being careful of the telegraph poles and some tall trees, look for a big flat rectangle of ground, then fly over a private hanger on the south side with the word ‘Airdrome' painted on the roof.” Pilots were then told to “circle to land from the northwest for the best wind condition” and avoid overshooting the field into the railroad tracks or brook.

Beginning in the early 1920s, airports began to use brief designator codes in addition to their full name. Some codes were random combinations of letters and numbers such as L39 for Ramona, California, while others were derived from the actual location or name of the facility. These codes evolved into today's three-letter designators that are included in printed guides and navigation charts.

Printed pilot directions became more precise and their maps, called charts, began to add new symbols to represent landmarks, towers, and other navigation aids. The codes and symbols have changed many times, but today's charts feature largely the same information as the 1921 printed guide.

The modern-day standard terminal arrival route charts illustrate a standard and well-tested route into an airport so that pilots avoid tall buildings and towers and land at the best wind angle. Other aviation charts use symbols to represent airports, jet routes, ground-based electronic and radio aids, and the most important radio frequencies a pilot will need to tune to along the course. Charts are issued in different scales, from a size similar to the original guide to the entire United States, down to an area of about 100 miles (161 kilometers) across but with much more detail.

The World Aeronautical Chart, at a scale of 1:1,000,000, shows 13.7 nautical miles (25 kilometers) in every inch (2.54 centimeters) of its chart, including only the largest landmarks like mountains, cities, and significant bodies of water. A Sectional Chart is more detailed with a scale of 1:500,000 and is used by pilots to navigate visually in slow and medium-speed aircraft, with one inch of chart equal to 6.86 nautical miles (12.8 kilometers). Sectionals show radio navigation aids, airports, controlled airspace, restricted areas and smaller obstructions along with important radio frequencies. The most detailed printed navigation aid is the Terminal Area Chart, with one inch equal to 3.43 nautical miles (6.4 kilometers). These charts show the small roads, elevations of the smallest towers and hazards to flight, and features in great detail surrounding a specific airport or city where precise navigation is most important.

A different set of charts marks the invisible roads used by pilots, called airways. The En Route High Altitude Charts are only for navigation when flying above 18,000 feet (5,486 meters). The Visual Flight Rules/Instrument Flight Rules Planning Charts show visual landmarks on one side and electronic and satellite aids on the other side and also come in a range of scales.

Modern-day pilots check huge directories to learn what rules to follow while at a field and what services will be available along their course. The U.S. Terminal Procedures Directory runs 16 volumes and lists airport requirements, taxi directions, and surface movement rules in the United States, Puerto Rico, and the U.S. Virgin Islands.

More than a dozen additional guides provide pilots with information on navigation, landing procedures, repair and fuel stations, and special airspace like over the oceans. Landing guides are printed in a format called approach plates, which can be folded into a size convenient to rest on the pilot's knee or clipped to the yoke of an aircraft just like the early airmail notepads.

All of these charts, airport guides, landing guides, and terminal procedure guides have traditionally been published by the federal government including the National Oceanographic and Atmospheric Administration, the Federal Aviation Administration, and the Defense Mapping Agency. The Jeppesen-Sanderson company is also a longstanding publisher of such material. In the future, private firms may perhaps produce an increasing portion of the charts, and companies may expand their own directories of airports, aircraft services, and navigation aids. 

--Roger Mola

Selected Bibliography and Further Reading

Clausing, Donald J. Aviator's Guide to Navigation. Blue Ridge Summit, Pa.: Tab Books, 1992.

Cook, Kevin L. “Road Signs for Airplanes.” Invention & Technology (Winter 2001): 60-63.

Illman, Paul E. The Pilot's Air Traffic Control Handbook.  Blue Ridge Summit, Pa.: Tab Books, 1993.

Kershner, William K. The Student Pilot's Flight Manual. Ames, Iowa: Iowa State University Press, 1993.

Komons, Nick A. Bonfires to Beacons: Federal Civil Aviation Policy Under the Air Commerce Act, 1926-1938. Washington, D.C.: Smithsonian Institution Press, 1989.

Spence, Charles F. Aeronautical Information Manual/Federal Aviation Regulations. New York: McGraw-Hill, 2000.

On-Line References:

FAA Historical Chronology. http://www.faa.gov/docs/A-INTRO.htm.

Federal Aviation Administration. Aeronautical Information Manual - Official Guide to Basic Flight Information and ATC Procedures. http://www.faa.gov/Atpubs/AIM/index.htm.

Original Air Service Map. http://www.airmailpioneers.org/flightinfo/Mapsoriginal.htm.