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Visual Aids and their Effect on Landing Success and Safety

E.S. Calvert
When an aircraft is following a straight approach path, there are six quantities which have to be simultaneously zero, whether the control is automatic or manual. Three of these are the displacement in the vertical plane through the approach path, and the first and second derivatives of this displacement. The other three are the displacement in the glide slope plane, and the first and second derivatives of this displacement. In good weather the pilot can obtain these six quantities directly from the natural visual indications with an accuracv which increases as the distance from the runway is reduced, and this enables him to control the aircraft within acceptable limits at each stage of the approach. The essential element in the natural indications is the horizon, and when this is blotted out by fog, the six quantities become confused, one with another, unless the observer is carried by a stabilised platform. It follows that since an aircraft is not a stable platform, the pilot is unable to obtain the six quantities from the visual indications, unless these indications are supplemented by artificial visual aids which restore the elements of guidance which are missing. The first part of this pa per shows how this confusion is produced, and the extent to which it can be resolved. If the , visual aids are defective in the sense that they do not resolve the confusion (the conventional runway lighting pattern is an example), then the pilot becomes liable to illusions at the moment of transition from instrument to visual flight, because the visual situation, as seen from the cockpit, can have many possible meanings. The pilot can only guess how much to move the controls, with the result that the final approach may be unstable and inaccurate. The failure rate in first attempts to land is therefore high, and even at major airports, may be as much as 30% in a meteorological visibility of half-a-mile. Where, however, the visual aids are designed on correct principles, the failure rate in this visibility is reduced to about 2%, with a substantial reduction in the accident rate. The operating limits are also lowered, and at London many operators now operate with a runway visual range of 500 yards, and a failure rate of about 6%.
WGL-Tagung, Augsburg, 1955
Conference Paper
21,0 x 29,7 cm, 8 Seiten
Jahrbuch der Wissenschaftlichen Gesellschaft für Luftfahrt, 1955; S.105-112; 1955; Braunschweig : Vieweg
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Dieses Dokument ist Teil einer übergeordneten Publikation012:
Jahrbuch der Wissenschaftlichen Gesellschaft für Luftfahrt 1955