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Aviation History
1951
1951 - 2125.PDF
522 PLIGHT PROBLEMS of the JET ERA Sir Frederick Bowhill Sums Up the Commonwealth Conference on Jet-Airliner Operation 1AST week we published a brief summary of the main con-clusions reached at the Commonwealth ad hoc meeting onJ the operation of turbine-powered aircraft, which took place in London from September 25th to October 5th. Sir Frederick Bowhill, chief aeronautical adviser to the M.C.A., was in the chair throughout the meeting. The conference itself was held mainly as a secret session, and consequently no official transcript is available of the delegates' deliberations. We have, however, received Sir Frederick Bowhill's personal summing-up of the highlights dis- cussed, and this provides a lucid picture of the ground covered. Sir Frederick found that the conference, as a whole, was vitally awareof the importance of communications for air transport. The outstanding requirement in this field, he says, is for greatly improved point-to-pointcommunications. He believes that the discussion emphasized the follow- ing points: (a) That because V.H.F. R T. (and V.H.F. D/F.) has apotentially greater range for high-altitude aircraft, it may become possible to provide complete cover on long overland routes; (6) that the inter-ference problem is accentuated and that every support should be given to an early increase in the number of V.H.F. R/T. channels to be usedin congested areas, and to the provision of additional channels as a special measure for high-flying aircraft, as and where the problem becomesacute; and (c) that R/T. discipline in the V.H.F. band should be improved. Dealing with the subject of fixed telecommunications, he says that theconference made it clear that the introduction of the Comet and similar aircraft will expose the deficiencies of the present services. There is aserious danger of aircraft arriving before the signals referring to them, or that information will arrive too late to be of use by aircraft or groundstation. Because of this, it is vital that there should be a speed-up of imple-mentation and an early completion of detailed plans. (In the U.K. an extensive programme of teletypewriter conversion on circuits terminat-ing at this end is now under way and a modern national Signals Centre is also being built.) Sir Frederick considers that the main conclusions to be drawn are (a)that all staging posts for gas-turbine aircraft should be interconnected by teletypewriter, preferably on landline, but alternatively using radio links,and with some form of tape-relay facility; (6) that there must therefore be early implementation of the internationally agreed plan, otherwise it willbe necessary temporarily to deviate from it and provide direct circuits; (c) that the greatest weakness in the present system is in the time takenfor handling messages at stations. (This, he suggests, could be improved by the use of electronic or mechanical links within the station, by trainingof staff, and by careful layout of the Signals Centre); and (d) that in certain special circumstances H.F. R,'T. might be useful for fixed services,for example, in cases where direct communication is essential but tele phone tie-lines cannot be provided. The serious world-wide shortage ofradio frequencies would, however, prevent any great extension of this system. Sir Frederick points out that the United Kingdom favours the generalintroduction of long range H.F. R'T. along the main trunk routes, although the transition from H.F, W/T. to H.F. R/T, is expected to takeseveral years. The Meteorological Aspect The importance of efficient meteorological services to the success ofoperations by turbine-powered aircraft were stressed during the con- ference. It is apparent, says Sir Frederick, that more detailed informationon hourly changes of surface wind and temperature at international air- fields is required in order to select the period of optimum conditions foraircraft departure. An appreciable advance in upper-air forecasting can- not be expected until the existing network of upper-air reporting stationsis improved and all meteorologists have had the opportunity to check the application of existing forecasting techniques or to develop more effectiveones. There is a particular need for accurate data between the height of 30,000ft and 50,000ft, and it is therefore essential that the world-wideradio sonde network recommended by I.C.A.O. be established at an early date. Because of the reduced accuracy of observations at high levels,research is required into the development of instruments to give more accurate readings than are possible at the present time. It is important,also, that all operators of civil turbine-driven aircraft make a point of accurate in-flight weather reporting during the first five to ten yearsof operation at high altitudes. In connection with the need for accurate landing forecasts, SirFrederick says the conference felt that further investigation could usefully be made into the application of radar for storm detection inareas where weather deteriorations are often rapid and local and where networks of surface reporting stations are sparse. On the implications of the navigational problem, he, points out thatcrews must be provided in the air with quick and accurate means of determining their position. There must be a means of checking fromground speed the extent to which the aircraft has run into winds of different velocities from those forecast—an important point in relationto high-velocity jet streams. Existing types of long-distance aid do not meet the requirement satisfactorily and there is evidently a need fornew development in this field. He mentions the possibility of an aid that would be completely air-borne. This, he says, would have obvious attractions to ground administrations, but there is as yet no indication that such an aid can be provided. The development of a really satisfactory long-distancenavigational aid could mean that at many places — except in areas where traffic densities require a very high accuracy of flight timing and naviga-tion—the in-flight transition from the long-distance aid to an approach aid could be made direct and without the necessity for a short or mediumdistance aid. In order to begin an economic let-down from cruising altitude, anaircraft needs to know its position at up to 200 miles from its destination, and during a let-down it needs to be able to check its progress andmaintain a separate flight path from other aircraft. In this connection Sir Frederick says the delegates agreed that theimmediate requirement in terminal areas can be met by V.H.F. D/F., M.F. beacons, and—most important—by 200 mc/s D.M.E. The U.K.has devoted considerable efforts to developing 1,000 mc/s D.M.E. to the I.C.A.O. specification, but there is no prospect of there being anadequate number of installations by the time the Comet is put into service. Most of the places on the Comet routes already have a formof 200 mc/s D.M.E. which was installed to meet the requirements of piston-engined aircraft. This equipment is likely to be required forabout three years and probably longer, depending on the rapidity with which 1,000 mc/s D.M.E. or some other system could be installed as areplacement. A good deal of discussion revolved round the choice between short-distance navigational aids, V.O.R, and D.M.E. and the medium-distance aid, Decca, Sir Frederick says. Arguments referred on the one hand tothe cost of V.O.R./D.M.E. networks and the low accuracy of the V.O.R, component; and, on the other hand, to the possible administrativedifficulties of providing Decca in certain localities. The M.C.A. has explained that it considers Decca the superior of the two systems ontechnical and economic grounds, and has also referred to developments of the integrated track range and track guide for use in certain areasoverseas. Integrating Jet Traffic In considering air-traffic control problems it was accepted that nopriority could be afforded to jets over other commercial air users and that it was important to achieve standardization of control proceduresin order to maintain a smooth traffic flow. The features brought out by the conference were that forecast take-off clearance times shouldbe accurately adhered to by control and aircraft, in order to reduce prolonged engine running and, therefore, heavy fuel consumption onthe ground; and that the aircraft should thereafter be permitted as unrestricted a climb as possible. En route, the traffic-control problemswere such that, since the altitudes were constantly changing, vertical separation would no longer be practicable. For descent from cruisingaltitude the aircraft requires freedom to conduct a steady descent, speed- ing it up at the end as required, rather than to be brought down tooearly and to have to fly level for a long time at a low altitude. For the let-down into the approach sequence, experience at LondonAirport has shown that the fuel penalty involved in bringing the Comet through the conventional stack at Epsom was less than the possible delayrisked by bringing the Comet down in a special procedure from 15,000ft, which would involve going through altitudes of other aircraft on theairways. However, it is very probable that, as yet more experience is gained on jets and as their numbers increase, the move will be to adifferent descent-pattern, although for this much better navigational aids will be required than are available today. The essential thing is toavoid delaying the jet aircraft at low altitudes. One interesting point brought out was that the effect of utilizationof high-speed aircraft necessitated a very short turn-round time, and this made it impracticable to adhere to the requirement that a fullflight-plan should be filed at least 30 minutes before take-off. The effect of temperature on turbine-powered aircraft is speciallyimportant and this fact is likely to make runway requirements critical. The concept of over-runs and the scheduling of operations in the coolerparts of the day will, it is thought, alleviate the problem at many airfields. At others, dependent upon stage length, full payload can be carried atthe reduced take-off weights imposed by runway limitations. In the ; extreme case, however, the cost of providing extra concrete will have to jbe weighed against the practicability and economics of jthe use of some ; method of assisted take-off. '. / • . " Much of the early discussion "Sat the conference'centred round thefigure of 9,600ft as a runway length for the Comet Series I. Taken out of its context, Sir Frederick points out, this figure can be misleading.He stresses the fact that both physical and financial limits are now being reached at many of the /world's more important traffic terminals, anathat designers and operators should both be left in no doubt of the neea to produce economic aircraft sufficiently flexible to use the largest numoerof airfields possible. „ It is important to remember, he says, that the temperature w***"piston-engiifed saircraft too. For example, the Stratocruiser would 10s 18,500 lb in all-up wjeight on a 9,000ft runway at 5,000ft at I.C.A.N- pi"15 degC. ' J In conclusion the much-discussed topic of turbine noise is 'nc?n°*i,(JThis affects not only the design and layout of airport buildings &ut ™ the general public living in the vicinity. All delegates agreed ttiat7Jtcareful examination and research must be made into this inip"J-Jj^ question. They were also of the opinion that investigations snow ^carried out to see whether there was any significant trouble to be exi e from exhaust gases in the terminal areas.
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