Be glad you don't have to navigate with these on your next flight...
1) In 1923, the US Congress funded the first lighted airway, known as the Transcontinental Airway System.
2) The first section of the route stretched from Chicago, Illinois to Cheyenne, Wyoming. The segment's location in the middle of the country allowed aircraft starting from either coast to depart during the day and reach the lighted airway by nightfall.
3) Lighted emergency airfields were funded along the route, spaced every 15 to 20 miles.
4) By 1933, the Transcontinental Airway System totaled 1500 beacons and 18,000 miles.
5) Airway beacons included a rotating white light, which created a quick 1/10 second flash every 10 seconds. In clear weather, it could be seen for up to 40 miles.
6) Each beacon had a set of red or green course lights below the white beacon, pointed along each direction of the route. Red lights were used on beacons in-between airfields, and green lights were use on beacons located at airfields.
7) Beacons were spaced 10 miles apart.
8) Each beacon's course lights flashed one of 10 letters in morse code: W, U, V, H, R, K, D, B, G or M. The letters represented the numbers 1 through 10, indicating the beacon's sequence on the route section.
9) Pilots remembered the sequential order using the phrase "When Undertaking Very Hard Routes, Keep Direction By Good Methods."
10) The standard beacon stood on top of a 70 foot concrete arrow, painted yellow and pointed in the direction of the course.
11) The Low Frequency airway system (NDB Airways) began to replace the lighted airway system in 1929.
12) Montana still maintains around 19 lighted beacons in the western section of the state, which you can find on the Great Falls sectional. They're indicated by a star, with the Morse code for the associated letter.