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Aviation History
1952
1952 - 0422.PDF
192 FLIGHT, 15 February 1952 RADIO and TRAFFIC CONTROL . . . the co-operation of their navigational equipmtnt; would transmit information derived from the aircraft to other elements in the sequence of automatic control equipment; and would automatic ally transmit back to the aircraft the clearances obtained. Estimates of probable traffic-densities in this country, R/T. frequencies available and the minimum to which essential R/T. communications could be cut in the landing sequence, lead to the conclusion that the use of R/T. should not prove the limiting factor in the movement-rate for a very long time, and that priority needs to be given to the development of other equipment first. Requirements of Turbine-engined Aircraft.—For over a year the M.C.A. has been examining the requirements for the successful introduction of turbine-engined aircraft. This work has cul minated in a series of flight trials with a Comet lent to B.O.A.C. last summer and it is fairly safe to say that, given a period in which the numbers of jet aircraft will increase steadily rather than by leaps and bounds, they raise a few problems peculiar to them selves, but serve rather to high-light difficulties under which piston-engined aircraft are already labouring in existing systems. One decision called for in the operation of all high-altitude transport aircraft is when to begin the descent from cruising altitude. If it is begun too late, an extended let-down will be required near or over the destination, with consequent loss of time and efficiency. If it is begun too early, the fuel consumption of the jet aircraft will be increased by the unnecessary time spent at low altitudes. Present thinking favours a gradual descent from cruising altitude beginning about 150 miles from destination and proceeding at normal rates down to about 20,000ft, at which altitude the cabin pressure will be equivalent to sea level. A more rapid descent may be made through the last 20,000ft, the rates of descent varying over fairly wide limits, but dependent to some extent on a comfortable floor-angle for the passengers. At the moment, appropriate navigational aids for the initial positioning would be Decca or, in sparsely inhabited areas, the Decca Integrated Track Range referred to previously, or D.M.E. on 200 Mc/s or 1,000 Mc/s. It may be mentioned ttiat the M.C.A. has already sponsored the temporary installation of prototype D.M.E. at Rome and at Cairo in order to obtain experience of its efficacy when used by B.O.A.C.'s Comet aircraft. The heading facility, obtainable on British D.M.E. receivers, is regarded as a useful additional asset. The need for rapid fixed communications to serve flights by very fast aircraft has been mentioned previously. On the air/ground side, the range of communications of V.H.F. will be extended considerably at jet cruising altitudes with a correspond ing increase in the area of interference. As an interim measure, it is intended to use special frequencies in the United Kingdom and Western Europe, and it is expected that the problem will be reduced when additional frequencies are brought into operation in the future. For efficiency and economy, weather diversions should be decided on before the aircraft has descended from its cruising altitude. This means that a flight watch on meteorological condi tions at the destination airfield and its alternatives should be maintained throughout the flight by the main meteorological office concerned, and it should be practicable to get the latest met. information through to the aircraft as quickly and as often as required. In addition, a flight watch will probably be maintained by the operators in order to pass operational information and advice to the aircraft in flight. Both these requirements point to the desirability of long-distance R/T. facilities on H.F.—a need which has already been recognized and met on certain routes operated by oiston-eneined aircraft. Finally, the need for informa tion on conditions in the upper atmosphere, particularly winds and temperatures, is important; and this will be reflected in the need for more "Rawinsonde" stations. The American Approach In the space available in this paper, only limited reference is possible to American thinking on these general problems, but this paper would be incomplete if it did not refer to the celebrated S.C.31 Report. The report appeared in 1948 and its preparation required the efforts of 85 experts and cost about 11,000,000. The grandiose scale of its recommendations was staggering. Put very simply, its objective was to raise move ment rates under all weather conditions to those obtainable under V.F.R. conditions, which can be very high indeed when separation in the landing sequence is largely left to the continuous visual information available to the oilot. Among the principles required to achieve this objective, S.C.31 laid down that information to be used in traffic control should be derived from ground equipment, whereas information to be used in the aircraft should be derived from_ airborne equipment; that safe separation of aircraft should be provided by automatic means and the flow of traffic should be controlled automatically; and that human operations should be reduced by mechanical or electronic means whenever possible. The latter devices were to be interlocked, so that they could not be misused or automatically set up a hazardous situation, and to operate on the "closed circuit" principle with "fail safe" indications of malfunctioning. The system should indicate when and where aircraft could be inserted into an existing traffic flow and should automatically transmit to the aircraft and display before the pilot traffic control clearance. These are but a selection from the requirements specified and they were to be met by some 20 different classes of equipment, including monitoring devices. The committee visualized that achievement of the ultimate plan would be via a transition plan. The cost was estimated at over $1,100,000,000. There are signs, however, that realization of the tremendous cost and effort involved in relation to the finances of the air transport industry, and the changed situation in the United States as the result of rearmament, have led to the time scale in S.C.31 being changed—and, apparently, some of the basic assumptions a'so. From such subsequent reports as that of the operational policy group of the Air Co-ordinating Committee issued last December, it looks as though the U.S. is now prepared to spend a much longer time in a transition phase and to take the experience gained during this period more into account when balancing the requirements and practicability of the ultimate plan. In particular, it looks as though they now hope to make use of V.O.R. for a much longer time and are resigned to the probability that for economic reasons they will not be able to rely on most aircraft being equipped with D.M.E. for several years. They are as convinced as we are of the value of surveillance radar in the terminal areas and are considering its application along their airways. Like ourselves, they are pressing ahead with the develop ment of transponders suitable for civil aircraft for identification purposes, and are providing I.L.S. and G.C.A. for instrument approaches. The most noteworthy differences of opinion between American and British thinking on these problems is, firstly, that the U.K. believes V.O.R. will prove inadequate for the densities and types of traffic to be encountered in a few years' time; and secondly, that the U.K. foresees the growth of cross-country helicopter services, and the consequent need to provide naviga tional aids for them, whereas some Americans at least consider that helicopters will only be used for local services serving districts around and in large cities. Universal Standardization of Aids Discussions on standardization of aids, such as those of the divi sions of I.C.A.O., tend to think of areas where the problems are most acute and to specify aids with those particular areas in mind. Experience has shown, however, that insistence on installing throughout a long route all the aids required at the busiest terminal on that route will make extravagant and unjustified demands for the provision of facilities at some staging points where the traffic is very much less and the general weather conditions may be very much better. Furthermore, at such places the needs of the local operators of feeder lines may be for equipment that can be carried in small aircraft and is lighter and less bulky than the equipment that can be accommodated in the large long-range aircraft. In these circumstances, the aids supplied at the small aerodromes should be usable by aircraft carrying the more comprehensive equipments without necessarily emulating the full scale of services provided in really busy areas. The exact selection must depend on the local conditions, and also on the proportion of traffic coming from long-haul operators, but the objective should be to decide on what is to be the highest common factor of equipment along the routes. It is, of course, arguable that it is a hardship for the long-haul operator to carry a comprehensive range of navigational equipment for a long way and at some cost-in space and payload if, for a large part of a route, ' he cannot utilize much of his equipment for improving the efficiency of his operations. On some routes, however, the only bad-weather areas where traffic is really dense exist at the ends of the route. In these conditions, it may be practicable for an aircraft to off-load some of its equipment at the first stopping place after a busy area and to pick it up ready for use at the same point on its way back and before entering the congested region. Such a procedure is alreadv in use bv some ocean-going ships for the highlv accurate navigational aid employed when close to certain coastlines and for entering harbours, but not when crossing the oceans. In conclusion [said Mr. Stallibrass] there is no doubt that equipment and procedures in use today enable regular services to be maintained as a routine in weather conditions that, before the war, would have confined operations to the occasional exploits of "intrepid birdmen". The emphasis on shortcomings has only been made here because one of our slyest temptations is compla- cencv and, for those close to the problem, the rate of progress should always seem maddeningly slow in relation to the ideal objective.
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