Diagram of a transcontinental duct system sign

In the United States, you can find huge concrete arrows, usually slightly overgrown with the surrounding vegetation. The icons visible from a great height are remnants of the navigation system, which was a very distant predecessor to the modern GPS.

The massive concrete arrows are a relic of an ambitious project relating to a pioneering era in the development of aviation. It was one of the aircraft’s first operational missions mail transport. With the development of this type of service, a problem arose: how to navigate to the destination without errors?

Whereas in places with diverse landscapes one can look for distinct navigational points, over endless meadows, the reference point for early pilots. The sun was over everyone. The situation was complicated at night, when due to cloud cover it was not always possible to navigate according to the stars.

Transcontinental Air Duct System – The Forerunner of GPS

The answer to these problems was an ingenious marking system – the system of transcontinental air corridors, which is essentially a gigantic postal infrastructure.

Diagram of a transcontinental duct system sign
Image source: © Public Domain

Diagram of a transcontinental duct system sign

The signs, built from 1923, consist of concrete arrows several meters long painted in a contrasting bright yellow. They were clearly visible from the air – subsequent tests showed this from an altitude of up to 16 km, which far exceeds the capabilities of old aircraft.

reflector of transcontinental duct system tower
Image source: © Lic. CC BY 4.0, Mark Wagner, Wikimedia Commons

reflector of transcontinental duct system tower

There was a concrete platform on each arrow, with a navigation tower 16 meters high. At the top of the tower – like a lighthouse – there was a rotating reflector with a diameter of 61 cm, which turned on after dark.

Both installations were additionally marked with colored lights, giving Morse code identification, and in areas where there were no nearby power lines, the installation was supplemented by a small house in which it was power generator.

Transcontinental airway system 1924.
Image source: © Public Domain

Transcontinental airway system 1924.

It only took a year for the arrows, spaced every twelve miles or so, to create a “road” connecting New York and San Francisco, that is, on the opposite coasts of the United States. It was enough for this 284 shares, and the route was less than 4.3 thousand. how much.

DeHavilland DH-4B Airplane - Civilian version of the Airco DH.4
Image source: © Public Domain

DeHavilland DH-4B Airplane – Civilian version of the Airco DH.4

The continent is covered with arrows

Cement navigation system It proved very effective – while the mail was carried by cars early at night, thanks to the transcontinental airline system, postal planes could fly around the clock.

The efficiency of the system was improved by the network of emergency runways, which were lit at night, located every several tens of kilometers.

One of the visible signs on Google Maps

One of the visible signs on Google Maps

Due to the ICAC system, the letter only took two business days to travel across the United States. The number of signs and routes grew rapidly – it only took a few years for the US to cover a grid of 1,500 shares, denoting 29,000 lines. How many airlines.

It soon turned out that a huge investment was no longer required – it was replaced by the development of radionavigation. Moreover, after the outbreak of World War II, it was decided that the visible signs from the air could be a navigational aid Enemy FlightSo part of the installation was dismantled.

Despite this, many tangible stocks have survived into our time, which – if we were not in the United States – we can check, for example, in Google Maps. A remnant of the once formidable navigation system are 14 signs still active and operating in Montana.

Łukasz Michalik, journalist at Gadgetmania

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