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Aviation History
1960
1960 - 0120.PDF
120 FLIGHT, 22 January 1960 SYSTEM SURVEY The DM All and Automatic Landing DURING an extensive briefing on the Airco D.H.121, reported onpages 102-104, some details were given of the work now being done to provide for automatic landing in airline service. The basicautomatic landing system for both the D.H.121 and the VC10 are developments by Smiths and Elliott Brothers of the work alreadycarried out by BLEU. Some of the background to this work—in which Britain can truly be said to lead the world—is now becom-ing apparent. First of all it is economically difficult to justify the expense of automatic landing equipment in commercial operation, especially if any elaborate ground equipment must be installed. An adequate system is itself on the fringes of the present state of the art and it may be as much as ten years before automatic landing is fully accepted as a routine procedure in "zero zero" weather. The reasons which Airco have stated for making provision forautomatic landing in the 121 are that it will provide improved regularity of operation with resultant benefits not only to theoperator but also to the passengers. Another important element is in improving overall landing safety, even in relatively clearweather. Airco consider that the D.H.121 will be flown by pilots of average ability and that, particularly in the European area, thecrew will require every possible assistance in lightening the work load. Automatic landing offers the best hope of reducing the presentweather minima of about 200ft and \ mile to something like zero, although other methods have been considered, particularly directorinstrument systems, special lighting and Fido. These alternative methods have not so far resulted in big reductions in minima andare in any case expensive. Airco consider it vital that the pilot should remain as aneffective monitor of the automatic system, but it is realized that a good deal of persuasion and practical experience will be requiredbefore pilots in general will believe in its effectiveness. They will have to be convinced firstly that the system is indeed safe and,secondly, that it can be effectively monitored. Not until this psychological task is achieved can automatic landing be considereda routine operational technique. As for the time scale in which this might be achieved, Airco stated that the initial stage of auto-flare would be in service in 1964 and that a period of familiarization and fault clearing would ensue. Following this the 200ft/i mileminima might be somewhat reduced, perhaps as low as 100ft/ a mile. The automatic equipment would subsequently be up-graded to automatic landing capability and its introduction would be followed once again by a familiarization period, during whichthe minima might again be slightly reduced. The stated objective is that genuine all-weather operations should become routine by1970. The fact that this date is 11 years after the RAF accepted and adopted the military Autoland system proved by BLEUindicates the magnitude of the task involved in developing a single- channel military system into a multi-channel system acceptable forcivil operations. With most present autopilots the minimum height certificatedfor operation is about 200ft. Autopilot operation must be rendered impervious to a runaway or disconnection failure right down tothe touch-down point and there are a number of approaches to this problem. Airco have initially chosen a duplex system in whichtwo autopilot sub-systems operate continuously with a constant comparison of their output signals. Following a significantfailure in one of them the other sub-system will cause the com- plete system to be disengaged, leaving the aircraft undisturbed in its flight path, but under manual control. Autoflare is the limit of automation to which this duplex auto-pilot could be applied because, for full automatic landing, it is vital that the system should survive one failure and continueoperating completely automatically without serious deviation. But the problem is less critical in the case of autoflare, when the filot would still be largely in control of lateral positioning. Airco propose that standard coupled approaches should be followeddown to a height of about 130ft, at which point the ILS glide- slope is too sensitive and possibly subject to deviations. Fromthis height aircraft would continue down to 65ft where duplicated radio altimeters would begin to control a flare-out to a point a fewinches below runway surface. Between 130ft and 65ft pitch atti- tude would be maintained by the autopilot on the basis of anaverage attitude established during the preceding coupled phase. During the whole approach an automatic speed control wouldhold approach speed to within ±2kt of a preselected value and power would automatically be progressively reduced during theflare-out to idling at touch-down. In this way pitch attitude and speed—and indeed the whole of the approach down to about 150ft—would be completely automatic, with the flight system and the ASI allowing monitoring by the pilots. During the attitude andflare-out stages the pilot's task would be to use aileron and rudder to make the final alignment with the runway by standard visualmethods and to kick off drift before touchdown. Appreciation of azimuth error is much easier than that of height error and auto-flare would thus greatly reduce the pilot's work load. Neverthe- less, the reduction in visibility minima would be limited by theazimuth alignment requirement to a value fairly close to the present one. BLEU research has shown that not more than 15secis a reasonable average time required to correct a lateral displace- ment of 200 or 300ft so that the runway must be visible at aheight of 150ft on a standard approach unless the approach aid is extremely accurate. It is essential that the autoflare should be a"simple, unfrightening operation" for any pilot. Airco stress that for both economic and technical reasons theautomatic landing system should require no additional ground equipment other than an ILS conforming to ICAO specification.Although the Leader Cable system is fully effective, the expense of installing it at a number of airfields might tip the scales tomake automatic landing too costly; and it is possible, if not indeed probable, that lack of open ground would prove an insurmountableproblem. Airco revealed little about the full-scale automatic landingequipment planned for the 121, beyond saying that it must be an integral part of the aircraft and that its ramifications extendinto the flight control, electrical and other aircraft systems. It must have as nearly as possible a standard instrument presenta^tion and it must be able to suffer a single failure—whether it be electrical, hydraulic or flight control—and continue to operatecompletely automatically. An important element of the 121 which is designed to cater for automatic landing is the hydraulic poweredcontrol system, the units for which are being designed by Fairey. (See Fig. 11, page 104.) Each of the systems has its own accumulators and a pump driven by one of the engines. An electric pump is provided to restore pressure in any one of the systems should its engine-driven supply fail. Finally, a ram-air turbine may be extended to ensure hydraulic power in the extremely remote case of failure of all three engines. The electrical system (Fig. 10, page 104) was also designed for operation either as a triplicate or triplex circuit based on three engine-driven alternators providing separate supplies for three flight control systems. Computers in Traffic Control •? ^ ~ FOLLOWING installation a year ago of an IBM computerin the FAA traffic control centre at Indianapolis, the centres at Pittsburgh, Washington and Cleveland have been similarlyequipped and linked together. The object is to compute and print flight progress information, to estimate arrival times overcheck points and to decide where conflicts will arise. The chain will shortly be extended to New York and Boston and thirtycentres will be included by 1965 to cover 128,000 miles of airways. IBM 650 computers with random access storage (RAMAC) areused to update the complete area picture, passing appropriate flight plans to neighbouring centres. Airway and beacon loca-tions, weather and programme instructions are stored and can be immediately consulted by the controllers. The BE A layout for the D.H.121 cockpit. Access to seats is outboard and the horned control columns keep the instruments in sight. Note the central area based on the pictorial map, with stand-by flight instruments above it. Central warning panel is at right and weather radar at left. The windscreen is large and the side windows may be slid open
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