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Aviation History
1959
1959 - 0887.PDF
444 AIR COMMERCE . . . FLIGHT THE HINGE OF HISTORY The wisdom of the controversial decision to standardize VOR/DMETas the international short-range navigation aid must be left to history to decide. This article reviews the special I.C.A.O. meeting at whichthe American aid was recommended in preference to the British area-coverage system. HOW will the world of 1975 look back on the recentCOM/OPS/RAC meeting of I.C.A.O., convened todecide upon an international short-range navigation aid? At the best, it would seem, with disfavour: for the world's twoleading air transport Powers clashed bitterly over their rival aids and reached a doubtfully honest and far from unanimous decisionon which one to adopt. Thirty-seven States attended at Montreal, and one other State,I.A.T.A. and I.F.A.L.P.A. sent observers. The meeting was chaired by Mr. J. W. Stone of Australia and the agenda wasdivided into three major parts: (1, 1) Determination of the precise nature of existing and expected problems in the variousoperational environments that involve the use of short-distance navaids; (1, 2) consideration of possible solutions in operationalterms; (2, 1) development of quantitative and qualitative require- ments to meet the operational solutions; (2, 2) review of thecapabilities of existing and proposed short-distance navaids and their relative availability; (3, 1) recommended practices and guid-ance material for short-distance navaids; (3, 2) recommendations in relation to other elements in the air navigation system. To cover this agenda, the meeting divided into two sections,committee A to tackle the comprehensive list of operational prob- lems and their solutions (agenda items 1 1, 1, 2 and 2, 1) and com-mittee B to examine the aids in question (item 2, 2) against the recommendations of committee A, which was also to tackleitem 3, 2. The committees worked in closed session, but there were alto-gether nine plenary sessions, one of which was devoted to a paper by Mr. B. Denicke on a U.S. Hyperbolic Navigation System testprogramme (New York Airways' experiences of Decca) and another to one by Capt. W. M. Masland (PanAm) of I.F.A.L.P.A.on operational aspects of the problem of short-distance aids. Working papers on various aspects of the subject were submittedby both U.K. and U.S. delegates before and during the meeting. No real difficulty was experienced by committee A in reachingagreement on item 1,1. This was an elaboration of the basic problem, described as "that of providing a system of short-distanceradio navigation aids which is capable of meeting most practically and economically the requirements of users both on the groundand in the air under a wide variety of environment conditions." But in the two succeeding items the committee ran into difficul-ties. Although the meeting was intended to view the requirements objectively, the U.K. and U.S. delegations (each regarding everyrequirement in the light of its own particular navigational aid) reached an impasse. Following a Canadian proposal, a two-country U.K.-U.S. working party was formed to try to thrash out the points of disagreement, and where necessary, "to agree todisagree." This resulted in the development of what were called "operational considerations applicable to the solution of theproblem described under agenda item 1,1. With some additions, these were adopted as a statement of system requirements. (Theywere later described privately as "the woolliest ever produced by an international organization.") But on four points the two delegations could not agree. Thesewere: (1) integration with precision aids for approach and landing and with long-distance aids; (2) the extent to which the short-distance aid should provide coverage with respect to altitude; (3) the extent to which the aid should provide assistance in theinstrument let-down service and (4) the characteristics of the system respecting air calibration requirements. They were sub-sequently settled by vote, as was the question of whether specific accuracy tolerances should be denned or not. On the latter pointthe wording of the resolution adopted was extremely vague: "the accuracy required should be the highest attainable that wascompatible with attainment of other important characteristics." Although, ideally, committee B should have had available theresults of committee A's work before reviewing the capabilities of the available aids, to save time B set about developing a detailedside-by-side comparison of the performance characteristics of Decca and VOR/DMET. Very slow progress was at first madein the detailed study of each delegation's technical working papers, and a new procedure was eventually adopted whereby delegatescould query points but could not enter into protracted discussion. In this way, committee B compiled Appendix A to the reportof the meeting: the characteristics of short-distance navigation aids presented by States for international standardization. Thiswork should not be underrated; it was a most comprehensive G/C. J. B. Veal, pictured here lwith some of his delegation, represented the United Kingdom at the special I.C.A.O. meeting on the short- range navigational aids comparative examination under 29 headings of the capabilities,stand-by arrangements and costs of Decca and VOR/DMET. In view of what was said or implied elsewhere during the meeting,it is of interest that under the heading of reliability (a score on which Decca was sharply attacked), the U.K. delegation had thisto say: "Earlier marks of Decca equipment used singly showed percentage serviceability varying from 90 to 97 per cent. ... Onthe evaluation Comet, no receiver faults and only two minor faults have occurred in 98 hr. In the trials of Decca/Dectra byS.A.S., the failure rate was 11.6 per 1,000 hr. . . . In the U.K. unscheduled interruptions of services from Decca chains are of theorder of a few minutes each year." Figures were not quoted for VOR/DMET, but it was stated that reliability is "far less impor-tant than fail-safe operation." While system characteristics were being studied in committee,the struggle continued in open session and through the media of working papers. In particular, a paper damaging to Decca on thescores of reliability and accuracy was read by the F.A.A. official in charge of the New York Decca-Bendix helicopter evaluation pro-gramme. In particular, a serviceability figure of only 83 per cent was given. G/C. J. B. Veal, leader of the U.K. delegation, after-wards pointed out that the accuracy figures quoted were "spreads," and not 95 per cent probability figures—as commonly acceptedby I.C.A.O.—and that, as far as reliability was concerned, the evaluation programme was only just beginning. The fact wasthat it was often impossible to service equipment once the day's work had started, and hence a fault on the first flight of the daymeant that every subsequent flight was marked against Decca. Another attack on the British equipment was made by I.A.T.A.;the association's representative, Mr. Besson, was quoted as saying that Decca provided no information from 30 to 40 per cent of thetime, 30 per cent of the time clear information was provided and during another 30 per cent partial information was provided. Thiswas followed by a statement in plenary session that "misunder- standings" had occurred and that the I.A.T.A.'s views should betaken as those in its earlier working paper. B.O.A.C. and B.E.A. specifically disassociated themselves from I.A.T.A.'s preferencefor VOR/DMET. Support for Decca was, however, forthcoming from Capt. Masland, the I.F.A.L.P.A. delegate, who contributeda lucid description of the difficulties of flying in the New York area. A particular point that he made was that no more VORscould be incorporated in the area because of frequency problems. The next stage of the meeting should have been a comparativeassessment of the two aids against the operational requirements put forward by committee A. This action was in fact proposedby the U.K. delegation but was opposed by the U.S. on the ground that adequate opportunity had been given for a study ofthe systems. A vote was taken and the U.K. was defeated. The U.K. then proposed an informal meeting of heads of delegationsat which divergent views might be resolved. The meeting was held, but minds were made up and nothing was achieved.At this point it was still possible for Decca and DMET to be recommended as dual standards; for DMET to be the standardand Decca the recommended practice, or vice versa; for DMET and Decca to be dual recommended practices; or for anotherconference to be called. But a compromise solution was rot acceptable to the U.S. or to I.A.T.A., and a vote was taken on theU.S. proposal to make DMET a complementary standard to VOR until January 1, 1975. By 20 votes to 4 with 12 abstentions, theproposal was upheld. As outlined previously in Flight (March 6), the decision has yetto be ratified by the I.C.A.O. council, although a precedent would be established were it not to do so. But whatever the council'sdecision, the area-coverage navigational aid with pictorial presen- tation will continue to be upheld as the best solution by theUnited Kingdom. The conference passed a recommendation that continued development of short-distance navigation aids should beencouraged; and Decca will undoubtedly exploit this to the full. And whether history proves the VOR/DMET decision to be rightor wrong, it has been affirmed that the U.K. will continue to extend the use of the aid in which its trust is placed. A. T. P.
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