Long before the days of radio (and those convenient little smartphone applications), the US Postal service began a cross-country air mail service using army war surplus planes from World War I, many piloted by former army flyers. To get the planes and everybody’s mail safely across the country by air, the postman was going to need a little help.
In 1924, the federal government funded enormous concrete arrows to be built every 10 miles or so along established airmail routes to help the pilots trace their way across America in bad weather conditions and particularly at night, which was a more efficient time to fly.
Painted in bright yellow, they were each built alongside a 50 foot tall tower with a rotating gas-powered light and a little rest house for the folks that maintained the generators and lights. These airway beacons are said to have been visible from a distance of 10 miles high.Visible from 10 miles high? That would be 52,800 feet, and altitude no airplane could reach at the time, and few can reach now. Perhaps the claim should have been 1 mile high, 5,280 feet above sea level. Realistically, it could have been .1 miles, about 500 feet above ground, where most early airmail airplanes flew.
This was high-tech navigation in the years after WWI. Think about that when you use your smart phone to navigate your way someplace. Or when you read about a modern aircraft landing at the wrong airport.
Very cool article here.