How accurate is the Omega navigation system?

Press, Volume CIX, Issue 31981, 7 May 1969, Page 12

How accurate is the Omega navigation system?

Mr Owen Wilkes, Mr F. A. McNeill, and others have claimed a high accuracy for Omega in fixing a position. A Reuter message from Washington dated July 2, 1968, is Often cited as crediting Omega with an accuracy of 200 yards. 1 The Omega Implementation Committee Report of 1966, however, says (page 1.6) that “by the time the Omega system can become operational, we are confident that the root-mean-square - fix error, for aU causes combined, will be about one-half mile in the day-time and ope mile at night.” The report adds that one single source of error in the system by itself accounts for discrepancies of threetenths of a mile (528 yards) in daytime and twice that at night. “This kind of error cannot be reduced by any known method, because it is a fact of nature.” the report savs. The Reuter message from Washington did say that location could be determined within 200 yards with Omega: but later paragraphs of the message make clear this refers to a specialised development of Omega which depends on the presence of a local subsidiary transmitter. “In normal usage, Omega will locate a plane, ship or submarine within a mile of its actual position at night and two miles in daytime (the report here confuses the day and night accuracies). However, in special circumstances, accuracies good enough for landing aircraft are possible: “The British Overseas Airways Corporation (8.0.A.C.) plans to use a method of almost continuous fixes for night and all-weather operations at remote African airfields which do not have modern guidance equipment.” This system is known as "dif-

ferential Omega” and doesil not provide absolute posi- I tion: It provides relative posi-1 tion between two Omega re- i ceivers in close proximity— , such as an aircraft and an airport—with an accuracy of 200 yards, even when both receivers may be miles out in their absolute position readings. In an address given in Nelson on April 18, 1969 (as reported by N.Z.P.A.), Mr P. A. G. Howell of the Canterbury

University physicists group is quoted as saying Mr Holy-, oake had been led to believe the Omega system would not be used for military purposes in an emergency. Mr Holyoake's statements give no indication that he has been led to believe this. They do say (December 4, .1968) that Omega is “not primarily a military system.” But they also indicate that he anticipates Omega’s use by both military and civilian users. Mr Howell is also reported as saying that the United States Government had put forward the argument that the system was required only for commerical purposes. The letter of the United States (Ambassador cited in the’

'Royal Society Report appears to contradict this. The ambassador described Omega as equally useful to commercial, private and military users. The Canterbury University physicists group in a statement reported on February 12,1969, stated they had documentation (from United. States naval sources describing Omega as primarily a military system with limited commercial application. Perusal of the sources cited by this group has revealed no such description, although it is true that in some Navai publications, aspects of Omega which Would be of interest to the Navy are emphasised. Even in. the much-quoted brochure of the United States Naval Electronics Laboratory, however, six' of the eleven suggested uses for Omega are civilian ones. It has been said by Mr Howell (Nelson, April 18, h 1969) that for all users except submarines the Omega system has already been super- . i seded by the Navy’s satellite ! system. However Kue- i, ! bier’s article in the journal, “Navigation,” states that!' for commercial navigation' purposes it will be necessary, to balance the higher accu- >! racy of satellites, which is not! necessary for commerical ! users, against the cost. A statement by the phy- ' sicists group (published April 15, 1969), said the “Naviga- ■ tion” article had criticised. Omega, among other things,! for having no non-military justifications. The Kiiebler article argues quite the contrary: he includes Omega among the systems which are satisfactory for commercial purposes, and points out its global coverage and other qualities, which earlier sys-l i terns lack.

Condensed from a paper by Nicholas Turner on the use of source material in the Omega controversy.