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Aviation History
1955
1955 - 0333.PDF
11 March 1955 333 The chart on the opposite page shows the facilities for the Frankfurt terminal area. The airways are marked with their bearings, the ranges, non-directional beacons (NDB), fan markers (in this case bone-shaped), and the facilities at Frankfurt itself. The latter include ACC (Area Control Centre), MET (meteorological information), RNG (radio range), VDF, V.H.F./D.F. and V.O.R. APP and TWR denote that the aircraft should call Frankfurt Approach or Tower on the frequencies listed on an accompanying table. The tines on the edge of the shaded range legs denote the "N" sector and the shaded outline of the airways show the presence of danger areas. These latter are necessary because of the presence of military airfields, each with its non-directional beacon. The black triangles show the reporting points, here all marked with non-directional beacons. The heights of the various danger and control areas are also shown. with the M.F. receivers, which takes the form of aural signals(morse As and Ns) transmitted in four lobes so arranged that, at the intersection of the various lobes, the As and Ns mergeto give a continuous steady tone in the earphones. These equi-signal areas are so adjusted in azimuth that they forma track guide in a certain direction, to indicate the position of an airway. If used as a terminal airfield marshalling aid theequi-signal legs are usually at right angles. These two arrange- ments can be seen on the chart reproduced opposite. Where ranges are located with the equi-signal tracks follow-ing the airway, an aircraft will fly outbound along a certain leg until it reaches a point where it meets the inbound leg ofanother range. In order to show when the intersection is reached, a beacon known as a fan marker is placed there. Thisusually transmits on 75 Mc/s and is picked up by an indepen- dent marker beacon receiver in the aircraft. It causes a light toflash in the cockpit, and when this occurs the pilot tunes his M.F. receiver to the new range frequency and follows the newequi-signal track. Along these airways there are reporting points, some voluntary, but most compulsory, over which the pilot callsthe air traffic control centre in whose area he is flying (either by H.F./R.T. or V.H.F.) to report his position. He will thenbe cleared to follow the next stage in his planned route at a height which will give him the necessary safe vertical separationfrom other aircraft in the same area. Radio range is still widely used on the North American continent and wartime installationsare still in operation in Europe, but it survives as a primary system mainly in the United Kingdom. In the U.S.A. the airways which previously relied on radioranges have now mostly changed over to V.O.R., with which there is complete coverage. The beacons associated with V.O.R.,however, are not necessarily situated on the airways themselves and are often slightly to one side of the required airway track.To facilitate airways flying by V.O.R. therefore, a system of "victor airways" has been instituted, whereby flight clearance isgiven either along the true airway track or along an alternative track passing directly over the nearest V.O.R. stations to it.This means that an airliner fitted with V.O.R. receivers (and almost all of them are) can fly directly outbound along a V.O.R.radial until it reaches a point where that radial intersects a given radial from another station. The receiver is then tuned to thisand course suitably altered. V.O.R. (V.H.F. omni-range) consists of a station transmittingin the V.H.F. band a continuous series of signals in every direc- tion. These signals cause a needle on a dial in the cockpit toindicate the bearing of the station relative to the aircraft's fore- and-aft axis, with much the same result as the A.D.F. Theindicator is often called the O.B.I, (omni-bearing indicator). As in the case of A.D.F., the signals from two V.O.R. receivers areoften fed to two needles on the same dial, so that cross-bearings can be taken to obtain a position fix. In accordance with an I.C.A.O. decision some time ago, astandard short-range navigation system was adopted and accepted by all member nations. This offered the advantage that all air-lines could thereafter hope to rely on the installation in all relevant traffic areas and so be able to operate without an exten-sive array of diversified airborne aids which would involve unnecessary expense. The system adopted was sponsored by theU.S.A. and called V.O.R./D.M.E. It was to consist of networks of V.O.R. stations, suitably distributed to coyer airways andsupported by D.M.E. (distance-measuring equipment) beacons. Thus an aircraft's position could be fixed by measuring thebearing and distrnce from a given V.O.R./D.M.E. facility. V.O.R. has worked well and is extensively installed in the U.S.A.In Europe there are as yet not very many, though more are being added, particularly in Italy and the Balkans. D.M.E. is also extensively used in the U.S.A. and Australia,but in Europe there are only experimental installations and results so far have not come up to expectations. Equipment inEngland (used principally by B.O.A.C.'s Comets) has been of the traditional Rebecca/Eureka radar interrogator/responderbeacon type, working on the 200 Mc/s band. This band, how- ever, is already part of the T.V. domain and not likely to remainfree for much longer. Navigation systems of the above types give position fixes by providing information on bearing and distance from a givenpoint. They are known as theta (azimuth)/R (distance) systems and are distinct from so-called "area coverage" systems. Theselatter transmit waves to form a hyperbolic lattice pattern which can be picked up in the aircraft by special receivers whose indica-tions are interpreted with the aid of charts to give a position fix. They mostly work on the M.F. band, using groups of stationsdeployed in "master" and "slave" patterns. A system of this type developed during the war is called Gee,and has a range of some 300 miles; both range and accuracy are affected by various ground and atmospheric characteristics. Itis not used by the airlines. A long-range development of Gee was called Loran by the Americans and, again using masterand slave stations this time on the L.F. band, it gives fixes at ranges up to 2,000 miles. Accuracy and range are again affectedby terrain and atmospheric conditions. In the standard refer- ence publications for all navigation aids, the patterns of accuracyand night effect are given for each of these aids. A further system is Consol, which was originally a Germanmilitary aid used during the war, discovered by the Allies and thereafter used by them also. As stated above, it can be pickedup on the normal M.F. receiver in the aircraft. Consol consists of a long-range electrically rotated beacon which transmits itscall-sign every minute or so, followed by a steady note for 30 sec on which the pilot can take a normal A.D.F. bearing. This isfollowed by a series of dots and dashes which the pilot counts as they are received. By knowing his approximate bearing fromthe station, and then finding the exact radial near this bearing on the Consol chart where the combination of dots and dashesoccurs, he will find the bearing of the station. Loran and Consol, having a longer range than either V.O.R.or normal M.F. facilities, are used as an aid during oversea crossings, particularly over die Atlantic. The Eastern Atlanticseaboard is covered by a Consol network and some Loran, with Consol stations at Seville (Spain), Lugo (Northern Spain), Quim-per (Brittany), Bush Mills (Northern Ireland) and Stavanger (Norway). The western seaboard has an equivalent system ofLoran, and both almost meet in mid-Atlantic. An airliner flying, for example from Idlewild (New York) toShannon, will use first Loran and then Consol as they are avail- able. In addition a constant check on position and track will bekept with the traditional astro-navigation methods, using a sex- tant and tables. During the crossing the airliner will report itsposition to the Atlantic control stations every hour by either W/T, or H.F./R.T.—mostly by the latter—the control stationsbeing at New York, London, Gander, Keflavik and Santa Mam (Azores). These stations, using 15 to 20 frequencies, are in theirturn in communication with each other, so that the aircraft's position can be reported to the agents of the airline companyconcerned on either side of the ocean. In the case of Pan Ameri- can , the New York office watches the aircraft up to 30 deg W,where the London office takes it over. In addition to astro navigation, D.R., Loran and Consol, theaircraft can make use of the facilities afforded by the ocean weather-ships. These are distributed over the North Atlanticas shown in the accompanying map and have radar sets with a range of about 90 miles. They also have V.H.F. for communica-tion and direction finding and non-directional M.F. beacons on which the aircraft can take a bearing with its A.D.F. Communica-tion can be established between ship and aircraft, weather and wind information passed, and position-fixing carried out. Theseweather ships drift and do not maintain their position with the accuracy of a land beacon. A special lattice system is thereforeprinted on the navigation chart, from which the ship can tell the aircraft where she lies in relation to her specified position. When leaving Idlewild the airliner is given permission beforeit takes off to fly out to sea through a particular control corridor in the A.D.I.Z. (Air Defence Identification Zones which surroundmost areas of direct U.S. influence) and told to report at the required point. Thereafter it follows its flight plan, and makesuse of all the aids and plotting methods available for position fixing. It is Pan American practice to carry a captain and two firstofficers (all pilots) one of whom will also be a trained navigator. For the crossing he will use only one chart, a 1 : 5,000,000-scaleMercator conformal projection covering the whole distance from New York to London, and giving just such information as he isliable to need. The only topographical features are coastlines and large rivers. In addition the chart will show A.D.I.Z. boundaries,Loran lattices and Consol bearing roses, weather-ship positions (with their position-error grids) and finally the latitude andlongitude lines. The principal colour on the chart is green, which while remaining visible in artificial light, does not unduly obtrudeitself over the pencil markings of the navigator's position plots. The track is marked as a rhumb line (straight) and all fixes recordedon it as they are taken. If there is a possibility, in view of weather and load conditions,that the flight can continue non-stop right to London, the track will be marked straight from the last A.D.I.Z. reporting point toa point on the south leg of the Shannon radio range, over the sea, I
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