Airmail Navigational Beacons and Concrete Arrows-Most Interesting Thing You’ll Read Today

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Scattered across the United States are a network of mysterious concrete arrows. They are often found in remote locations or areas difficult to access. Some will be accompanied by a small shack, a few have a metal tower affixed to their base. Many are in good condition while others have succumbed to nature. The shape and direction of the arrows vary, but it is clear they served the same purpose.

The purpose was important: helping early pilots navigate U.S. transcontinental flights at night.



In a era before radar, pilots used ground-based landmarks for guidance. This solution worked for flight during the day, but grounded pilots at night. Before long, a system of beacons was established across the United States to guide airmail pilots around-the-clock. When radar and radio communications made the beacons obsolete years later, most were torn down or abandoned.

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Beacon Tower System

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Aircraft of the era lacked the advanced electronics for navigation during night flights or through inclement weather. Long before the advent of radio guidance or Instrument Flight Rules (IFR), pilots were limited to visual guidance, using landmarks to chart the route.

Flying at night was out of the question; bad weather and limited flight times meant delivery was limited and still spotty in frequency. The service was indeed faster, but it lacked flexibility and reliability of operations.

By 1924 the Postal Service developed a solution that was effective, if not elegant.

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A system of ground-based navigation beacons extending from New York to San Francisco would help pilots fly across the country at night and ultimately be the world’s first such system.

The early iterations of the system used approximately 1,500 airmail beacons, each constructed roughly between 3 and 5 miles apart. The beacons featured a 50-foot tower with rotating lights placed on top of concrete foundations in the shape of giant arrows measuring between 50 and 70 feet long. To increase visibility of the concrete arrows, they were painted bright yellow.

The first towers contained acetylene-gas powered lights which were fed by fuel stored in a shed at the base. At the top of the towers, a rotating beacon with 5,000 candlepower and would flash every ten seconds.

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In clear weather the beacon lights could be seen for 10 miles (16 km). Below the main white beacon, a secondary set of red and green lights would flash a Morse Code letter to identify the beacon to pilots.

To accommodate for emergencies, intermediate landing fields were established every 25 miles along the route. The fields were constructed with rotating incandescent electric lights mounted on 50-foot towers set to sweep six times per minute. These less-common emergency field beacons were visible up to 75 miles away.

The program was an immediate success and continued to expand throughout its operational life. By the end of the first year the airmail service had 18 terminal airfields, 89 emergency airfields, and more than 500 beacon lights in operation.

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But by the 1930s, navigation and radio technology had improved to allow flight without land-based visual guidance. The Low Frequency Radio Range (LFRR) system began to replace older visual-based systems. The airmail beacon program would continue to operate full-scale until 1933, when technology advancements and the higher cost of operation during the Great Depression – finally rendered it obsolete.

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Today

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