An airway beacon (US) or aerial lighthouse (UK and Europe) was a rotating light assembly mounted atop a tower.
[3] Use of the lighthouses has declined with the advent of radio navigation aids such as NDB (non-directional beacon), VOR (VHF omnidirectional ranging) and DME (distance measuring equipment).
[citation needed] In the Netherlands, gas holders were painted with an arrow pointing north and two letters identifying their location.
Today, most of the beacons have been removed, but the State of Montana continues to maintain several as navigation aids in mountainous terrain.
[6] One beacon is preserved for historical purposes in Saint Paul, Minnesota[7] at the Indian Mounds Park on a bluff overlooking the Mississippi River.
[8] A rotating airway beacon has been in continuous operation at the summit of Rocky Butte in Portland, Oregon since 1929, though it was officially decommissioned during the 1960s.
Recently, the beacon at Grants, New Mexico was restored for historic preservation, using original items found at other nearby sites.
[14] To help remember the letters and their sequence number, pilots memorized the following: "When Undertaking Very Hard Routes, Keep Direction By Good Methods."