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Aviation History
1963
1963 - 0318.PDF
FLIGHT SYSTEMS 302 FLIGHT International, 28 February 1963 Approach and Landing: Situation Display AN advanced design stage has been reached at Borehamwood on the coaming-mounted approach and landing situation display which the Transport Aircraft Controls Division of Elliott Brothers (London) Ltd are providing for the automatic landing system of the VC10 and subsequent types. Although it incorporates indicator, director and failure-warning elements, it is not strictly a flying in strument, but an autopilot error-recovery indicator giving con stant indication of localizer and glide-slope error in relation to the corrective capability of the autopilot. It thus provides for the first time a dynamic indicator of autopilot effectiveness. Previous indi cators of this general type have shown overall control demands related to the ability of a human pilot and not to the necessarily limited authority of an autopilot. Several changes have been incorporated since a prototype in strument was exhibited at the SBAC Show last September, but the visual details of the display are now fairly well established, and a prototype demonstrated to company and airline pilots. Elliott worked for two years as a private venture on the system before they received a firm order last month to produce a working prototype system in one year's time. Development was difficult mainly be cause Elliotts had to extract requirements out of many pilots' experience in order to determine exactly what kind of information was needed. Pilots knew very well that they wanted a dynamic monitor, but were unable to say, until they had seen successive versions of early display elements, what form the indicators should take. The dynamic autopilot-manoeuvre envelope display seems to offer an admirable solution. The display box is flat, has a maximum depth of Hin and one unit is mounted on the top surface of the glare shield in front of each pilot. The displays are associated with the left and right monitored autopilots, monitored radio altimeters, and monitored radio equipment, but each contains failure warning flags for both of the autopilots and the dual throttle system. The front glass of the instrument is sloped inwards at 45°, avoid ing any reflection from surrounding light sources, the face of the instrument itself being lit probably in pure white to retain maximum contrast between the black and white symbols. The pilot normally adjusts his seat before an approach so that his line of sight is parallel with the top of the glare shield. In this position, the display will not interfere with his normal field of view, but there will be a very slight cut-off in diagonal vision. In the initial installation, the display will be mounted on rails to allow fore-and-aft adjustment, but a fixed setting about 3ft from the eyes will probably be adopted later. Basically, the display consists of a white field positioned round a fixed ring mark, the width and depth of the field decreasing during the approach to represent the narrowing manoeuvre capability of the autopilot in the final stages. At the same time, the location of the fixed ring mark within the white field indicates what deviations from localizer and glide-slope exist at any given moment, and pro vides an indication of error development or correction. If the PITCH ERROR INDICATOR RADIO ALTIMETER HEIGHT, The Elliott Approach and Landing Situation Display for showing autopilot performance and capability during an automatic landing ring moves outside the white field, the autopilot can no longer produce an adequate correcting manceuvre and the pilot must take over manually. This should be a rare event, which could arise, for example, from intermittent failure of the ground radio equipment or from severe wind conditions. The fixed ring mark is painted both black and white so that it shows up clearly against either white or black backgrounds, and it may be made into an active flashing indicator, if desired. Because the vertical depth of the white field is necessarily limited by the shallow instrument case, an additional height-error display is added on either side of the white field to intensify error cues in the pitch plane. A rotating cylindrical indicator capable of showing either a complete black background or moving horizontal white lines is positioned behind the white field. The cylinder remains black and blank while pitch control is correct. If a small deviation occurs, three thin white lines appear on the cylinder, which begins to rotate slowly to give nose-up or nose-down indications. Should the error continue to increase, the cylinder not only rotates faster, but the lines become thicker. This is an application of the attention- getting capabilities of movement in a specially designed display. The movement also gives directional information in the early stages of attracting the pilot's attention through his peripheral vision. The instrument combines a "soft" display with rapid attention-getting following an error. If the approach is progressing normally the pilot does not see the stripes, but he receives an un- mistakeable and powerful indication as soon as an error develops. The sense of rotation is such that the aircraft appears to be moving past a stationary pattern of stripes and the pilot receives a demand to fly in the direction of the glide-slope centre. The operation of the rotating display can, incidentally, be en hanced by including phase-advanced terms, which cause the stripes to broaden momentarily when an error first occurs and then narrow down again. The whole of the centre of the display, including the white field Various instrument indications in relation to displacements from beam centre and influence of cross-wind. The shaded rectangular fields indicate usable areas for autopilot control OUT OF ALIGNMENT IN AZIMUTH NO PITCH ERROR LINES MOVING SLOWLY DOWN (A) PITCH ERROR AND AZIMUTH ERROR iiTcir\c MAwmiwot ON BEAM CENTRE LINE MANOEUVRE LIMITS DISPLACED
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