Aerial Route Flashing Beacon The U.S. Army Air Service placed beacons like this one around airfields in the early 1920s. They were also stationed three miles apart along the established air mail routes, and at night, pilots could see their constant glow from 10 miles away. A switch automatically turned the light on at night or on overcast days and shut it off during daylight hours. Developed from a Swedish light used by the British Air Ministry on the London to Paris air route, this American Gas Accumulator Co. beacon used acetylene gas to produce 5,000-candlepower flashes 150 times a minute. Click here to return to the Early Years Gallery.