Airway beacon

An airway beacon was a rotating light assembly mounted atop a tower. These were once used extensively in the United States for visual navigation by airplane pilots along a specified airway corridor. Approximately 1,500 airway beacons were constructed to guide pilots from city to city, covering 18,000 miles (29,000 km). Most of the beacons are gone, but The State of Montana continues to maintain several as navigation aids in mountainous terrain. One beacon is preserved for historical purposes in Saint Paul, Minnesota at the Indian Mounds Park on a bluff overlooking the Mississippi River. Recently, the beacon at Grants, New Mexico was restored for historic preservation, using original items found at other nearby sites.

A large concrete slab, in the shape of an arrow, was located near the base of each beacon. Many of these arrows remain today, some of which are visible from satellite pictures, even in urban settings.

An airway beacon has two distinct light characteristics: A revolving narrow white light beam about 5 degrees wide in azimuth and a set of fixed colored course lights of about 15 degrees width.

The rotating beacon features a 24 inch (610 mm) parabolic mirror and a 110-volt, 1 kilowatt lamp. spinning at 6 rpm, creating a quick 1/10 second flash every 10 seconds. In clear weather they could be seen for 40 miles (64 km). Montana took steps to modernize their beacons encasing newer light systems in clear domes.

Just below the white beacon, a set of red or green course lights point along each airway route. Red lights denote an airway beacon between landing fields while green denotes a beacon adjacent or upon a landing field. These course lights flash a Morse code letter identifying the beacon to the pilot. Each beacon is identified with a sequential number along the airway, and flash the red or green course lights with the Morse code ID of one of 10 letters: W, U, V, H, R, K, D, B, G or M. The letters represent the digits of 1 through 10 (W = 1, ..., M = 10). The course lights turn on for 0.5 second for a dot, 1.5 second for a dash with a 0.5 second between each dot or dash. A pause of 1.5 seconds separates each letter.

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