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Aviation History
1972
1972 - 1938.PDF
FLIGHT International, 27 July 1972 139 of seeking to improve flight safety, and that it is doing so with success. I am also quite sure that nothing whatever would be contributed to this process if we were to depart from the very long-standing practice of declining to publish any regular statistics related to flying hours. Crude accident rates would mean very little in themselves in the absence of the mass of detailed and technical analysis which is required to interpret their real significance (and which could not be disclosed for reasons of security), and the effect of publishing them would be to invite speculation on every occasion on which a minor fluc tuation occurred. The likely consequence would be that the Directorate of Flight Safety would be obliged to devote time to an unhelpful and inconclusive run ning debate at the expense of its proper job, and nothing would be gained in terms of morale or safety. I hope you will not think this too un helpful a reply. I am grateful for the interest you have shown in this subject and I recognise the concern on which it rests. But I have no doubts myself that it is right to adhere to the existing practice. Naturally, I shall always be ready to give as much information as I can about any particular accident or series of accidents which is a cause of public concern; but this is a different matter from the regular publication of crude statistics, and I hope you will accept my reasons for believing that there are overriding objections to the latter. • more Defence on page 142 Avionics Right, the aerial and rack-mounted computer. The unit mounted on the former is the Gunn diode microwave generator and pre-amplifier. The pilot's indicator face (below) shows 045 actual track and 07S demanded course to way-point 3 New Doppler from Marconi M ARCONI-ELLIOTT AVIONIC SYSTEMS is to market an advanced light weight J-band Doppler radar in con junction with Canadian Marconi, whose commercial survey resulted in the project being launched 18 months or so ago. Designated AD.2510, the radar is designed for retrospective installation in light military attack aircraft, though the two companies foresee a substantial business-aviation outlet. Simplicity of design for single- seat operation was the main aim. The equipment consists of a Doppler sensor (a fixed aerial about 17in square, using a Gunn oscillator as the microwave radio-frequency source, and a pre-amplifler), equipment-bay- mounted navigation computer, pilot's indicator and console-mounted control unit. It operates in a largely digital mode and weighs 32-51b. At present there is no specific application in mind—relatively simple systems such as this are bought off- the-shelf—and development will be complete by the end of the year. The price has not been fixed, but will lie between £10,000 and £20,000. Despite its simplicity the AD.2510 embodies a number of new tech niques. The antenna employs printed- wire stripline in place of the more conventional slotted wave-guide, which cuts production costs by simpli fying the design. The 12 or 34 ATR signal-data converter makes extensive use of MSI (medium-scale integra tion) microcircuits for reliability, and the multi-layer circuit cards (made, incidentally, by Marconi) are connec ted to one another through a mother board, thereby dispensing with much of the wiring. The system operates on the normal, sequentially switched, four-beam prin ciple, but the 13-3GHz output signals are continuous-wave with frequency modulation. This gives relative im munity against multipath effects (which may arise from the carriage of under-wing stores, for example). The accuracy is predominantly that of the heading reference employed and the way in which it is used. The along-track and across-track velocity information itself is accurate to within +0-15 per cent. Over a lhr flight, the error figure of 1-32 per cent when used with a magnetic heading input improves to less than 0-5 per cent when a better heading reference is used—a compensated directional gyro or transfer-alignment DG, for example. Obviously this will degrade slightly if the pilot indulges in a lot of violent manoeuvring, but groundspeed computation continues up to +40° in both pitch or roll. If the aircraft exceeds this the system reverts to its memory mode, using the most recently computed ground- speed. The equipment relies on way-point data for position updating, and both the pilot's indicator and control unit reflect this. The former contains nine displays or functions:— actual track being flown, command bearing to next way-point, track error angle (both coarse and expanded), distance to next way-point, actual ground- speed, time-to-go to next way-point, update switch, selected-destination counter and memory indicator. The main facility provided by the control unit, or destination selector, is a removable drum containing ten plastic cards which can be punched with way-point data during pre-flight briefing. The information so stored can be checked for accuracy and se quence using a simple test set before the drum is taken back to the air craft. Before take-off the pilot selects the card containing the first way-point data, and the display is immediately referenced to those data. As the air craft passes over each way-point the pilot updates the system by switching the indicator to Hold (thus freezing the display) and pushing the Update button. He then selects the next way- point on the control unit. This unit contains heading and Doppler failure warning lights. The correction factor for extensive over- water missions is also selectable on the unit. A test facility on the control unit checks out the operation of the equip ment, while ATE (automatic test equipment) can be plugged into the navigation computer for ground test ing, M.W.
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