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Aviation History
1955
1955 - 0332.PDF
AIRLINE NAVIGATION A Summary of Facilities and Procedures EFFICIENT navigation for the airliner means safety,operation to schedule in almost all weathers, and henceprofit. Position and course to the destination, or to a source of help, must be known at all times and must be suscep- tible to positive supervision from the ground. The crew of an airliner must themselves know at all timeswhere they are, how far they are from a waypoint or destina- tion, how long it will take them to get there and how muchfuel they will need to do so. With a view to achieving these objectives, airline operators install equipment suitable for usinga variety of facilities which exist on the ground; and, according to the type of aircraft used, each flight is planned in detail toachieve a given stage distance with adequate reserves of fuel, yet with the maximum payload. Since payload depends uponthe type of aircraft and the route involved more than upon the method of flying that route, this article concentrates on thenavigational rather than on the flight-planning aspect. Airline navigation resolves itself into facilities, methods andprocedures. Their distribution and use can best be introduced by describing the equipment carried, for example, by a PanAmerican Airways DC-6, and how this is used during an Atlantic crossing. Both the equipment and its use are typicalof airline practice, though of course there are many small variations from company to company. The Pan American DC-6, then, carries duplicate V.H.F. com-munications sets giving at least 50 different channels, H.F R/T. receiver and transmitter (again duplicated), a Loran receiver,two M.F. receivers with A.D.F. loops and cockpit indicators, two V.O.R. receivers with two cockpit indicators, duplicatedI.L.S. equipment, Sperry Zero Reader, Sperry A.12 autopilot and a radio altimeter. Of these the Loran receiver, the V.O.R. receivers and theI.L.S. equipment, are used principally in conjunction with their related ground installations. The M.F. receivers, on the other hand, are approximately equivalent to normal medium-frequencyreceivers and can be used for a variety of purposes. Without the loop facility they can pick up ordinary radio broadcasts,special meteorological information transmitted by various agencies at certain times, and such of the navigation aids as donot require special receivers. These latter aids include medium- frequency radio ranges, and Consql. Meanwhile the automatic loops tied to each receiver are usedto obtain a bearing, relative to the aircraft's fore-and-aft axis, of the station transmitting (when within range), whether thisbe a normal broadcast (B.B.C. Light Programme, Droitwjch, for example), or a particular M.F. radio facility specially sitedfor navigational purposes. It is, of course, also possible to arrange for an M.F. navi-gational beacon to transmit information verbally or in code so that it can be used for two purposes at once. A.D.F. is usefulbecause of its flexibility, but for various reasons does not supply all the airliner's navigational requirements. First, it is not along-range aid, and secondly it is not sufficiently accurate and free from static interference in certain atmospheric conditionsand geographical locations; thirdly, identification of a beacon is not always free from ambiguity. There is a further navigational aid called V.A.R. (visualaural range) which is basically a development of I.L.S. and which can therefore be picked up with the I.L.S. receiver.V.A.R. consists of two beams transmitted by a ground station approximately at right angles, one being visual, i.e., fed intothe I.L.S. cross-pointer meter, and the other aural and fed as a tone signal into the pilot's earphones. There are a number ofthese ranges on the Continent, particularly as track guides for the Berlin air corridor, but V.A.R. is not an accepted standardI.C.A.O. aid. It is also possible to feed a V.O.R. radial bearing signal into the I.L.S. vertical cross-pointer needle to facilitateinstrument course-holding. The normally accepted radio range is an M.F. aid, picked up
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