OMEGA was the first truly global radio navigation system for aircraft, operated by the United States in cooperation with six partner nations. It enabled ships and aircraft to determine their position by receiving very low frequency (VLF) radio signals in the range 10 to 14 kHz, transmitted by a network of fixed terrestrial radio beacons, using a receiver unit. It became operational around 1971 and was shut down in 1997. Hope this helps. It was replaced in the VC10 by a swept up Litton Inertial Nav system which was downgraded by RAF so that it was no better than the Omega! I think the Navigation branch wanted to ensure that they could not be replaced!