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Aviation History
1962
1962 - 2315.PDF
588 FLIGHT International, 11 October 1962 K 0 [ . i^ jnHBff iwf7; ~*«t© OJ f 56T » -1 —/** "N 0 t t 1! N A V. *•* V / '..**o i tftU5 TO GO J ' . . A °N • sst cousse £ jO 6 J- ^|w«t 'iT^ i 7 8 V ^T MUE5 TO m % sitcootst \^ J o g £ c) CHA-34A For trons-At/ontic f'ying w/thout human nav/gators (see item on this page), TWA now use duplicated Bendix Doppler and computers. Course and distance of two legs of the flight are set on the control panel shown here and the computer then indicates distance to go and across track error. The change from leg A to leg 8 is automatic. The captain is shown in the other picture setting the computer inputs in the roof console of a Boeing 707 AIR COMMERCE. TWA Relies on Doppler ON Monday last week, October 1, TWA flew the first two Atlan tic crossings without human navigators, relying instead on dup licated Bendix Doppler and computers operated by the pilots. On the day before, 37 of TWA's 55 navigators were "furloughed" with agreed separation pay. Thus begins a new chapter in the trans-Atlantic navigation story—begins, because the navigators are still strenuously contesting the new "do-it-yourself" technique, and because the eventual result of Doppler navigation might be reduced ATC separations over the Atlantic. TWA have been testing Doppler in Boeing 707s for at least two years, proving to themselves and to the FAA that they can thereby dispense with navigators without loss of safety or track-keeping accuracy. Many other airlines are using Doppler, but only TWA has so far taken the plunge and reduced their crew complement because of it. In preparation for navigatorless polar flights between San Francisco and Europe, TWA are now proving their Doppler installation in far northern latitudes. The Airline Navigators Association has recently adduced reports from military and civil research agencies and from its own members to support an apparently well-founded theory that the Mid- Atlantic Shelf has magnetic anomalies, which significantly interfere with compasses and radio propagation, causing unpredictable and changing navigation errors of significant magnitude. Further research is needed, say the navigators. Nevertheless, it was fully evident when talking with the crew after their first all-Doppler crossing that their navigational accuracy is rather better with this equipment than without it, that it is very simple to operate and that the pilots have complete confidence in their ability to cross the Atlantic without navigators. TWA pilots are not navigator-trained, as are many in BOAC, for example. But the captains are quick to point out that the performance of the human navigators was only less accurate, on occasion, because they did not have the use of Doppler. It is simply a sad fact that the new navigation device is also very simple to operate. TWA now have their 12 Boeing 707-33Is fitted with Bendix DRA-12 Doppler and CNA-24A computers, all units except the aerial being duplicated (the CNA-24A is based on the computer designed by Computing Devices of Canada Ltd). Outputs, besides the basic Doppler drift and groundspeed, are distance to go and distance across track on two legs, with automatic 10 miles-to-go warning and changeover to the second leg. Autopilot coupling is possible, though not yet provided, and a certain amount of switching is possible to allow a good unit in one Doppler system to replace a failed one in the other. Failure of one Doppler chain would be treated much like the failure of an engine, with consequent on- the-spot decision as to whether to continue or turn back, but the basic drift and groundspeed outputs could well be used to complete a crossing, even without a navigator. Across-track accuracy depends, of course, upon the accuracy of the aircraft compass system, and TWA swing their Bendix Polar Path gyro-magnetic systems once a month, and run spot checks during the month. Magnetic variations as high as 32° are en countered over eastern Canada. TWA have charts giving average variation over 10° Longitude sectors and these are simply applied to the compass systems at appropriate intervals. During a routine trans-Atlantic flight, the Doppler is switched on before take-off and begins to track between 50 and 90ft above ground. During the initial airways legs, Doppler performance is observed and checked. Using tracks pre-computed on the ground, the pilots set the distance and course of the first two over-ocean legs into the computer and start it running at station passage over the final airways VOR beacon. The cone of confusion at jet cruising heights is said to be sufficiently clearly marked to raise no untoward errors. ETAs can be calculated from Doppler ground-speed. Approximately one hour after and before coast crossing the pilots take and plot a fix by Loran or Consol to check the Doppler- derived position, and radar fixes are taken from any of the Ocean station vessels encountered, but no parallel plotting chart is kept. Alterations to flight-planned course can easily be inserted in the Doppler computers. Pilots say they spend between 15 and 20 minutes plotting fixes and reporting position during the over-sea flight and that they are no more occupied with navigation than during normal airways flying over Europe or the USA. It is estimated that the Doppler operates on memory, without direct radar measurements, for about 2 per cent of any six-hour crossing. Pilots include Doppler-estimated wind velocity position reports. The two inaugural navigatorless flights, from New York to London and Paris, made landfalls respectively ten miles and two miles off course after 1,750 or more miles over sea. TWA say that Doppler saves, on the average, between seven and nine minutes' flight time per crossing and is sufficiently accurate to allow the crew to conform to the ADIZ reporting points east of Canada, the lateral tolerance of which is 20 miles. The London flight was four miles south of track according to the fix plotted by radar from station vessel Charlie. The fix from Juliet was 15 miles south of track, but the vessel changed its own position estimate twice while the fix was being taken. Whatever the navigators claim, with their livelihood at stake, the TWA technique has been fairly exhaustively tested and super vised by the FAA as part of its project Accordion study of North Atlantic navigation. The most convincing argument is to hear the pilots report on Doppler navigation. They are obviously quite convinced that their installation works and that the method is feasible. Without any reflection on the skill of the navigators in pie-Doppler days, Doppler is apparently allowing better track- keeping accuracy, with the obvious implication that the present wide ATC separations on the Atlantic could be reduced if all aircraft made full use of Doppler. The human problem of disposing of navigators belongs, at the moment, to TWA alone, but the prospects of reducing Atlantic separations are universally attractive and of major importance to all operators. It remains to be seen whether the equipment will ultimately be judged adequate for this purpose. There are still many who will hotly protest, even in the face of TWA's experience.
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