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Aviation History
1946
1946 - 1879.PDF
SEPTEMBER IgTH, I946 FLIGHT AIR TRAFFIC CONTROL^ The Demonstrations at Bassingbourn : Two Suggested Control Schemes Individual Navigational Aids Described f I AHE visiting delegates of the Provisional International I Civil Aviation Organization are being shown at the -*- R.A.F. Station, Bassingbourn, two schemes for the ground control of air traffic. The items of equipment on which both schemes depend are being exhibited separately with suitable working mock-ups, and the R.A.F. have taken the opportunity of showing several other recognized aids to navigation which could be used as the basis for other possible methods of control. The Ministry of Civil Aviation and the R.A.F. have quite different systems which, however, are similar in their common dependence upon radar and radio, air discipline, and accurate flying. Both systems are new to civil avia- tion, but the R.A.F. Transport Command have experi- enced considerable operational success in the Far East with the Service method. Although the civil scheme has not been tried operationally, Gee, upon which it depends, is a tried and proved navigational aid. In fact, all the radar equipment is very similar to that used so successfully by the operational commands during the war and is in- valuable in its resistance to interference from static. Exer- cises are continually being flown, and we were recently given the opportunity of witnessing complete and highly successful demonstrations of both systems. Below is a description of the two schemes, and also, very briefly, of the equipment which is demonstrated and on exhibition. An interesting feature in both systems is the fact that the aircraft, while awaiting landing instruc- tions, are '' stacked '' horizontally, a method which has many advantages over vertical separation in those parts of the world where icing may be heavy. M.C.A. DEMONSTRATION AIR TERMINAL: If landing at Bassingbourn in the direction 2600 M. aircraft would be routed either direct or on to one of the master lattices to reach the "gate." Only whole-number hyperbolae are shown in this diagram. The Ministry of Civil Aviation's air traffic control scheme depends primarily on the use of Gee, the principles of which are described later. Although a special Gee pattern is not necessary, it is a prerequisite that within a radius of 50 miles from the airfield the hyperbolae are as nearly straight as possible and cross at approximately 90 deg. For each direction of approach two Master lattice lines are selected to cross 8 miles downwind of the runway; this position is called the " gate," and it is at the "gate " that the traffic control system ceases, and the aircraft is then dependent upon preselected approach systems. When about 70 miles from the airfield, the aircraft sends a W/T message with its position and time at which it expects to leave Area Control and to enter Approach Control—which starts within a radius of 50 miles of the airfield. The Controller then decides, with the knowledge of othei aircraft movements, air speeds and wind velocity, the course which shall be flown by the aircraft to reach the " gate." If no other aircraft are approaching the gate, then a direct line can be ordered, but if some delay is neces sary in order to allow other aircraft through, a computed course is ordered so as to bring the aircraft on to one ol the Master lattice lines, maintaining in both cases a height of 2,000 feet. On reaching the Master lattice line, the aircraft homes along it to the gate. The Controller ar ranges passage for each aircraft through the gate in such a way as to permit landing in a steady flow and, at present, at an interval of three minutes, which also permits take ofis between landings. R/T is used where language per mits, but W/T is possible. If for any reason an overshoot is necessary, the aircraft turns to starboard through 180 deg. on to a lattice line parallel to the approach lattice, and continues at 1,000ft until reaching the crossing Master lattice, when a signal must be sent to Control. The Controller then decides when the aircraft shall turn on to the approach lattice. The Ministry intends to use Airfield Control Radar in conjunction with the scheme to enable the Controller to maintain a complete picture of the horizontal position of all aircraft within his control area. R.A.F. Poor Visibility Lauding System The R.A.F. system of controlled landing loi aircraft in poor visibility has the advantage of being mobile. On any airfield where an Eureka beacon may be put down and a Babs van placed in position, then the system may be worked with aircraft carrying an orbit meter and the necessary Rebecca apparatus. All four of these items are individually described later. Although this system has been evolved to meet military requirements, it may be applied to solve similar problems in the control of civil air traffic. The requirements for operating the scheme are, first of all, an Eureka beacon, around which aircraft can orbit at given or preselected radii. . Secondly, each aircraft must carry an orbit meter to ensure accurate flying on the circular track around the airfield. A Rebecca must also be carried to operate the orbit meter and to interrogate Babs for the beam approach. The sequence of events is standard and direc- tion from the ground is very simple. Aircraft
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