The Evolution of Airway Lights and Electronic Navigation Aids

In the early days of flight, there were no navigation aids to help pilots find their way. Pilots flew by looking out of their cockpit window for visual landmarks or by using automobile road maps. These visual landmarks or maps were fine for daytime, but airmail operated around the clock. In 1919, U.S. Army Air Service Lieutenant Donald L. Bruner began using bonfires and the first artificial beacons to help with night navigation. In February 1921, an airmail pilot named Jack Knight put this to the test with his all-night flight to Chicago from North Platte, Nebraska. Knight found his way across the black prairie with the help of bonfires lit by Post Office staff, farmers, and the public.

By July 1923, Bruner's ideas for lighted airport boundaries, spot-lit windsocks, and rotating beacons on towers had taken hold. The Army opened an experimental lighted airway between McCook Field in Dayton, Ohio, and Norton Field in Columbus, a distance of 72 miles (116 kilometers).

Beginning in 1923, the Post Office worked to complete a transcontinental airway of beacons on towers spaced 15 to 25 miles (24 to 40 kilometers) apart, each with enough brightness, or candlepower, to be seen for 40 miles (64 kilometers) in clear weather. On July 1, 1924, postal authorities began regularly scheduled night operations over parts of this route. In 1926, the Aeronautics Branch of the Department of Commerce took over responsibility for building lighted airways. By June 1927, 4,121 miles (6,632 kilometers) of airways had lights. By 1933, 18,000 miles (28,968 kilometers) of airway and 1,500 beacons were in place.

Each tower had site numbers painted on it for daytime identification. At night, the beacons flashed in a certain sequence so that pilots could match their location to the printed guide that they carried. Besides the rotating beacon, one fixed tower light pointed to the next field and one to the previous tower, forming an aerial roadway. Official and emergency fields were lit with green lights while dangerous fields were marked with red.

Because of this effort, by the mid-1920s the swashbuckling days of airmail operations had begun to pass. The lone pilot dressed in a leather flight suit who sat in an open cockpit battling the elements to deliver the mail was romantic but inefficient. The Postal Service began to focus on safety and reliability as well as on expanding operations. It established minimum lighting requirements for all airmail stations: a 500-watt revolving searchlight, projecting a beam parallel to the ground to guide pilots; another searchlight projecting into the wind to show the proper approach; and aircraft wingtip flares for forced landings. It also prescribed that all landing fields should be at least 2,000 feet by 1,500 feet (610 meters by 457 meters) to allow plenty of room for landings. As a final safety device, the requirement for a searchlight to be mounted on airmail airplanes was appended to the Post Office's set of requirements.

The use of lighted airways allowed pilots to fly at night, but pilots still needed to maintain visual contact with the ground. A really useful air system demanded two-way voice communication and the ability to find out about changing weather conditions while in flight. But in 1926, pilots could only receive weather information and details about other planes in the air just before takeoff. If conditions changed while flying, the ground had no way to warn them. A pilot, too, had no way of communicating with the ground.

The Bureau of Standards began to work on two-way technology in December 1926 at its experimental station in College Park, Maryland. By the next April, it had an experimental ground-to-air radiotelephone system operating that could communicate up to 50 miles (80 kilometers). Soon after, a transmitter installed at Bellefonte, Pennsylvania, on the transcontinental airway, successfully communicated with an airmail plane 150 miles (241 kilometers) away.

In October 1928, the Aeronautics Branch installed a group of new radio stations to complement the 17 it had inherited from the Postal Service. It also began sending voice information to help pilots navigate, first by radiotelegraphy and then by teletypewriter. By the end of 1934, there were 68 communications stations and many pilots could request navigation help by two-way radio.

In 1928, the Bureau of Standards also developed a radio navigation beacon system, and in 1929 the Aeronautics Branch standardized a four-course radio range whereby pilots listened to audio signals to determine if they were on course. The Aeronautics Branch stepped up installation of four-course radio ranges, and this technology became standard for civil air navigation through World War II.

In September 1929, Army Lt. James H. Doolittle became the first pilot to use only aircraft instrument guidance to take off, fly a set course, and land. He used the four-course radio range and radio marker beacons to indicate his distance from the runway. An altimeter displayed his altitude, and a directional gyroscope with artificial horizon helped him control his aircraft's orientation, called attitude, without seeing the ground. These technologies became the basis for many future developments in navigation.

The Aeronautics Branch began formal flight inspection of airway navigation aids in 1932. Six pilots were each responsible for about 3,500 miles (5,633 kilometers) of federal airway. Through 1935, the antennas for transmitting and receiving radio range beacons were improved and more instrument navigation tests conducted. September 1935 marked the first simultaneous transmission by radiotelephone of voice and weather information and radio beacon signals for navigation, and by the end of 1938, six stations were complete and 159 were in progress.

In May 1941, the Civil Aeronautics Administration (CAA) opened its first ultrahigh-frequency radio range system for scheduled airline navigation, eventually expanding use of such equipment to 35,000 miles (56,327 kilometers) of federal airways. In 1944, with wartime advances in radio, the CAA began testing a static-free, very high frequency (VHF) omnidirectional radio range (VOR) that allowed pilots to navigate by watching a dial on their instrument panel rather than by listening to the radio signal.

After the war ended, in 1946, the U.S. Department of Commerce took over 200 air navigation facilities that the U.S. military had built in 68 foreign countries. Domestically, in 1947, the CAA opened Skyway One, a pair of 40-mile (64-kilometer)-wide paths from Washington, D.C., to Los Angeles. The next year it added Skyway Two between Seattle and Boston. In June 1948, the CAA installed the first high-powered, low frequency, long-range navigation facility on Nantucket Island, Massachusetts, mainly to aid ocean flights. Similar 300-foot (91-meter) towers were built on both coasts and in Omaha.

By the middle of 1952, 45,000 miles (72,420 kilometers) of VHF and VOR airways, referred to as Victor airways, supplemented the 70,000 miles (112,654 kilometers) of federally maintained low frequency airways. The CAA began to shut down the low and medium frequency four course radio ranges.

In 1961, the FAA began using distance-measuring equipment on its entire system. This equipment allowed aircraft to determine their distance from known checkpoints in order to confirm their position. The first Doppler radar version of the VOR system made it more accurate for longer distances.  

The FAA participated with the National Aeronautics and Space Administration in the first public demonstration of a new system in March 1967 that would use orbiting satellites to transmit navigation data from aircraft to ground stations. The test was followed by further development of aircraft antennas to send and receive satellite messages.

In October 1969, 16 area navigation routes were developed. Previously, pilots had flown directly toward or away from the ground-based radio navigation aid (a VOR or VORTAC). This aid transmitted a course along invisible lines called radials. With area navigation, pilots could fly any pre-selected flight path roughly within the boundaries of that local system while an onboard computer tracked and reported the aircraft's position. Courses could be established along the shortest path within these route segments. By the end of 1973, nearly 156 high-altitude area navigation route segments were available.

The last airway light beacon from the system begun in the 1920s was shut down in 1973. By the middle of 1982, the first of 950 new radio navigation aids equipped with solid-state construction and advanced features was installed. Navigation aids, the computers supporting the system, and cockpit displays and instruments to send and receive navigation data all improved steadily throughout the 1980s.

In October 1994, the FAA requested a government/industry study of the Free Flight concept, which may allow pilots to choose the most efficient routes without having to fly the prescribed routes that connect the navigation aids. Further development of Free Flight, including flight tests, continued. In 1998, the FAA and its industry partners began limited application of some of the capabilities associated with the concept.

Additional navigation technologies are in partial use or development, including the Global Positioning System both to locate and help control aircraft by satellite, the Future Air Navigation System for remote and oceanic flights, and the Communication, Navigation and Surveillance for Air Traffic Management system. These technologies combine the need for point-to-point navigation and for higher quality voice and data communication with the need for air traffic control--the safe separation of aircraft from hazards and other aircraft.

--Roger Mola

Selected Bibliography and Further Reading

Bilstein, Roger E. Flight in America, From the Wrights to the Astronauts. Revised Edition. Baltimore: Johns Hopkins University Press, 1994. 

Burkhardt, Robert. The Federal Aviation Administration. New York, Frederick A. Praeger, 1967.

Gilbert, Glen A. Air Traffic Control: The Uncrowded Sky. Washington: Smithsonian Institution Press, 1973.

Komons, Nick A. Bonfires to Beacons: Federal Civil Aviation Policy Under the Air Commerce Act, 1926-1938. Washington: DOT/FAA, 1980.

Preston, Edmund. FAA Historical Chronology, Civil Aviation and the Federal Government 1926-1996. Department of Transportation, Federal Aviation Administration Office of Public Affairs, Washington, 1998. Available at http://www.faa.gov/docs/A-INTRO.htm

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

Poole, Robert W., Jr. “Building A Safer and More Effective Air Traffic Control System.” http://www.rppi.org/ps126.pdf.

Thompson, Scott. “The History of Flight Inspection in the United States of America.” http://avstop.com/Stories/inspection.html. Also at http://avnwww.jccbi.gov/icasc/fh(united_states).html