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Aviation History
1977
1977 - 0073.PDF
;»•:*:,;,,,™ As the airways become more congested and pressures to conserve fuel increase, the world's airlines arc demanding ever more accurate navigation. MIKE HIRST reviews the systems which have made the human navigator redundant. S!iB;i;i; M '.v, civil airliners today IP, without navigators on routes ih.ii were navigational)* demanding in the ""' -" distanl past. Smaller aircraft* have occa- -ioually followed routes demanding :;i.-.n navjgaliona] "kill Inn Inn.' i.in:., airliners have ilovvti such stages 11 • "lai i'. toi IN m\ •.•,:,-:. l |. to a) b n veai - mo ii was usual to 1111.i , n.,-. I-.-...H.I amongst the flighl crew of long- rangi aii lim i • bill lati l\ tin m ip-and > ompass man ha> ji.iesl.io> there)ore arises: lu\e pilots suddenly developed . ordinary sense of direction? The answer oi course is "No.* Instead, i <ost airliners now carry an "automatic nay matin ' and navigation is carried out by pilot-opeialed black boxes 1 he appearance of these systems on long-haul flight decks has led to smaller flight crews—even though aircraft continue to grow larger, faster and more complex—and on small aircraft has opened up new possibilities. The development which has so radically changed the shape of air navigation is the digital computer. As the cost of the computer has fallen, it has proved a cheap substitute for human labour in the performance of routine calculations. For practical purposes, the cemputer is also infallible, even though it relies implicitly on the qualify of the data and program input by its human operator. But given the right data in the right order, a computer should always produce the right answer. About twenty years ago air navigation was ripe for a computer take-over, with digital technology just beginning to emerge. Navigation has always been something of a number-juggling business, and so it was fortuitous that some of the navigator's information began at this time to come in a form assimilable by an airborne computer. The increased accuracy and range of radio aids brought about the computer's airborne debut. Typical early short-range radio aids were the radio-range and non-directional beacon (NDB). Both used wavelengths which could suffer serious propagation effects, they were limited in range, and were prone to natural interference. While the the NDB is still in use as a local aid throughout the world, the most important short-range radio aid is the very-high-frequency omni-directional range (VOR). VOR was widely used immediately after the Second World War, and remains a useful navigation source because its radiation pattern produces 360 identifiable radials. As well as homing on to the beacon, one can select (and either home on to or steer away on) a particular radial. The recently introduced Doppler VOR (DVOR) generates compatible signals which appear identical to a conventional VOR airborne receiver. Co-located with VOR transmitters one often finds distance-measuring equipment (DME). This provides an indication on the flight deck of the slant range from the DME base to the aircraft, again generating information which a computer can readily digest. Long-range navigation development has been less straightforward. The Second World War created a heavy demand for long-range position-fixing systems, and several different systems were evaluated when civil aviation later began to pioneer new longdistance routes. Some have been
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