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Aviation History
1968
1968-1 - 0234.PDF
FUGHT International, 26 December (968 UK jet transports allows Cat 2/3a certification without a HUD, relying on a failure-surviving automatic landing system. Some of the Cat 2 systems certified by the FAA rely heavily on flight director instruments. For poor-weather operations, a HUD integrates more logically into such systems. In particular, McDonnell Douglas have carried out detailed investigations with a HUD in evolving a Cat 3 system for the DC-9. During visual manual approaches, the HUD can perform a useful and valuable function in improving the accuracy of the approach and reducing pilot workload, but the safety record of existing big jets is very good and has been steadily improving ever since they were introduced into service. Nevertheless, in the new generation of airliners, the cost The new small 80- series HUD projection unit, arranged for glare-shield mounting in an existing jet air liner, retains the 4in lens and wide-angle optics of its larger predecessors of a HUD generally represents a smaller proportion of total aircraft cost, while the judgement of approaches with ultra- large aircraft is unlikely to prove easier. The cost-effectiveness of a HUD system is therefore much improved. Additionally, increasing operation of current jets from airfields which have previously handled only piston-engined traffic introduces a requirement for an aid self-contained within the aircraft, allowing an accurate approach to be flown even in the absence of ground aids. Equipment Development Timescales Because of the inherent but correct caution in the application of new systems to passenger-carrying aircraft, a long time elapses between initial feasibility discussions or experimental demonstration and an in- service date. For example, the first automatic landing was achieved by BLEU more than 20 years ago, but the first full automatic landing carrying fare-paying passengers was not made until this year. Military use of inertia! navigation was reasonably commonplace by 1960, but civil airlines have only just accepted it in practice and the Boeing 747 will be the first airliner to enter scheduled service with an inertial navigator incorporated at the prototype stage. So much for the lack of airline endorsement of HUDs to date. What developments have there been over the last few years to alter the situation? Although, as already mentioned, there has been no basic 1065 change in HUD concept as far as civil equipment is concerned, continuous progress has been made over the last few years in all the features which have discouraged civil operators from adopting HUDs. This covers both flight trials experience and equipment development. The Belfasts equipped to full automatic landing standard have carried out flight trials over the last 18 months with the Elliott HUD system fully integrated with the AFCS. Much valuable experience has been gained and the HUD is con sidered to be such a useful aid, when fully and properly integrated in this way, that all Belfast HUDs will probably be modified to this standard. The flight trials of the Elliott HUD in a DC-9-30 at Long Beach in 1967 were exceptionally successful. A total of 25 pilots representing a cross-section of airline, military, FAA and manufacturing personnel evaluated the equipment in flight and all of them commented very favourably on the system's characteristics, capabilities and performance. McDonnell Douglas have probably carried out more work on operational and installation aspects of HUD systems than any other airframe company, and it will be surprising if this is not followed in the near future by further flight evaluation. Other HUD flying has, of course, taken place at the Royal Aircraft Establishment and at the Centre d'Essais En Vol at Br&igny, but the Belfast and DC-9 trials were with HUD systems integrated with an AFCS in a way which is representa tive of civil operations. This flight experience has shown, inter alia, that there is no discernible reduction in the pilots' ability to acquire cues in low visibility providing that the light loss in the combiner glass is kept to the order of 25 per cent. Development on the equipment front has been aimed at reducing size and weight; at simplification (and therefore cost- reduction); and at improving flexibility and integrity. The Elliott 80-series range of head-up display systems, first announced in July this year, represents a particularly successful approach to these objectives. Use of a laminar-beam cathode-ray tube has allowed a dramatic reduction in the size of the projection unit. Coupled with modular unit design, this has greatly eased the installation problems. Modular design allows the projection unit to be offered in a number of different configurations, with different optical Systems to meet glareshield or overhead positioning without additional development. Developments in symbol generation and processing elec tronics, based on techniques proved in Elliott military HUD systems, have resulted in an extremely flexible system. Changes in symbol format, which will almost certainly occur from airline to airline and within airlines as related avionics are improved, can be accommodated by altering a single matrix board in the HUD system. Additionally, full self- monitoring facilities have been included, as well as self-test to line-replaceable unit level, in order to give acceptable system integrity and allow for normal airline maintenance procedures. By these developments, the overall acceptability of HUD systems to the airlines has undoubtedly been improved. Development and trials are removing, point by point, the objections raised in the past and there is good reason for anticipating airline adoption in the not-too-distant future. Left, Elliott-Automation military HUD and associated pilot's controller in the RAF Short Belfast. This system has 18 months' flight experience as an integral part of the automatic landing AFCS. Right, an important operational application of HUD in airlines is the projection of flight-path vector and touchdown prediction during visual approaches. By placing the threshold marker at the threshold and retaining the vector circle on the depressed horizon line a correct glide-path can be maintained with ILS aid
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