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Aviation History
1953
1953 - 1489.PDF
I 13 November 1953 643 MAN-TO-MAN TALK-DOWN —The Ekco Approach Aid Type CE 71 in Operation AS he plunges once more into the slough of British winter weather, many a pilot finds himself expending nervous ' energy in speculations concerning approaches and diversions. All too often at this time of the year those pilots who cannot normally claim the support of all the ponderous machinery of flight control in I.F.R. conditions, are firmly "grounded" by low cloud and poor visibility, though weather above, say, 3,000ft may be ideal; or, perhaps, having started unscheduled point-to-point flights, they find themselves harassed by "clamps" which partially close in airfields of destination during transit. It is in such circumstances as these that the Ekco approach aid is particularly useful at the smaller civil airfields not equipped with comprehensive (and expen sive) facilities. A member of Flighfs staff recently had the opportunity of seeing the Ekco equipment in operation in just the conditions outlined above. The opportunity arose when Southend Municipal Flying School's Gemini took off at dusk for G.C.A. practice; the cloud base was eight-eighths at 1,300ft, with tops at 3,000ft. Visibility below cloud was obscured partly by gathering darkness, partly by radiation-fog which had already formed in the valleys around Southend. In fact, details were indistinguishable beyond a few hundred yards' range. A gooseneck flare-path laid on the grass runway, two sodium lights marking the threshold, and red obstruction lights on a church and a large house on the approach; all these were invisible at 800 yd. Yet in these conditions a series of accurate and comfortable approaches was carried out. With simple V.H.F. R/T. in the aircraft, normal control-tower facilities and the Ekco one-man G.C.A. equipment, the Gemini was repeatedly brought in to the transition point from which it was in each case possible to make successful touch-downs. The Gemini was first homed over the airfield by V.H.F. D/F. and then picked up and identified by the G.C.A. controller with his own D/F. and radar beam. At this point the Gemini was flying at 1,500 to 2,000ft. I.F.R. A base leg was flown and the operator passed QNH, runway details and instructions for undercarriage and flap settings. When the turn on to the cross-wind leg was made, the ground was in sight vertically below; but horizontal visibility was limited to a few hundred yards. It was not until die aircraft was well settled on its glide-path, at a rate of descent of 300ft/min, that the ground became clearly visible; even then, the airfield was indistinguishable in the dusk and patches of mist. Following normal G.C.A. procedure, final checks were called, heading and height corrections passed, and obstacle-clearance break-off height given (300ft). At three-quarters to half a mile from touch down, the flare-path was dimly visible, and the sodium threshold- markers came into view. At between half and a quarter mile from touch-down the controller called "look ahead and land." On this occasion the G.C.A. operator was under training. With practice, it is possible to bring the aircraft practically down to the hold-off point with very little visibility. This was in fact accomplished on one occasion when ground fog had suddenly formed on the airfield. Larger aircraft, such as Dakotas, have also successfully been talked down. These talk-downs, in which the procedure corresponds almost exactly to mat of the full-size G.C.A., are accomplished with compact, simple equipment, costing just under £4,000, operated by one man and housed in a normal Service-type cara van. It consists, in fact, of a combination of a 3 cm radar installation with a V.H.F. D/F. receiver, the radar dish being mounted on a common rotatable shaft with the D.F. aerial, so that the axis of the beam coincides with the null direction of the D.F. aerial. The radar dish is permanently linked in azimuth to the D/F. aerial, but is independendy controllable in elevation. Thus, the radar pencil beam can be trained on the aircraft with the D/F. and elevated as necessary to secure positive radar contact. The radar display is a simple "A" scope presentation, calibrated in nautical miles in two ranges, 0 to 4 and 0 to 16. Two scales show the position in azimuth, and elevation of die dish aerial. A series of adjustable contacts operated by cams on the scale-drives illuminate lamps beside the "A" scope to indicate whether the aircraft is on die glide-path and on track. A microphone and loudspeaker mounted on the set cover R/T. communication. The whole equipment is manually swivelled by a "handlebar" so that the operator faces the aircraft being followed. The aerial is elevated by twist-grips on the handle- The simplicity and compact ness of the Ekco Type CE 71 equipment is clearly shown in these illustrations. The radar and V.H.F./D.F, aerials are mounted on a common shaft with the rotating main unit inside the caravan. The set is manually swivelled by the "handlebar" as shown in the lower illustration, and very little space is required for the whole installation. bar, and the D/F. sensing switch is operated by one thumb. The equipment is extremely simple, but completely efficient. Although obviously not capable of handling a stream of traffic, it is quite adequate for the needs of an airport such as that at Southend. For a cost which must be a fraction of that of full- scale G.C.A., approaches of the same type and of equal accuracy can be achieved. The dimensions, weights and power requirements of the Approach Aid Type CE 71 are as follows. The body of the rotating rack assembly measures 4ft high x 2ft lin wide x 2ft 3in deep; the assembly requires a distance between floor and out side roof of 6ft lOin. The weight of the complete assembly, including aerials but excluding R/T. communication equipment, is approximately 600 lb. The floor-standing rack, normally supplied with the equipment and housing the control unit and R/T. communication equipment, measures 4ft 4in high x 2ft lin wide x 1ft 8in deep, and weighs approximately 300 lb. The mains voltage stabilizer is a separate unit measuring 2ft 4in x lft 3in wide x 1ft 4jin deep, and weighs approximately 165 lb. The complete installation comprises the following 15 units: The rotating rack assembly, with radar and D/F. aerials, which houses the following seven items: indicator unit, 3 cm trans mitter/receiver, indicator power unit, transmitter/receiver power unit, D/F. receiver, D/F. receiver power unit, and distribution unit; then the mains voltage stabilizer and the mains trans former unit; and finally the 4ft floor-standing rack housing the control unit, R/T. transmitter, R/T. receiver, and the R/T. receiver power unit. The equipment is available for operation from standard mains or locally generated supplies.
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