Patent GB-909221-A (GB)
Title: Radio instrument approach and landing system
IPC: G01S19/15
Filed: 1960-08-02
Abstract: 909,221. Radio navigation. BOEING AIRPLANE CO. Aug. 2, 1960 [Oct. 5, 1959], No. 26736/60. Class 40 (7). In an aircraft radio landing approach system a first transmitter Tf, Fig. 1, is laterally displaced from the runway L at the approach end thereof, a second transmitter Tr is located at the far end of the runway in alignment with the centre line thereof and the aircraft carries means for indicating the magnetic bearings of the two transmitters from the aircraft, the aircraft heading and, during the final approach phase, the drift angle due to side wind. The transmitters Tr and Tf are omni-directional and transmit continuously at different frequencies, the transmitter Tf being more powerful than the transmitter Tr. As shown in Figs. 2 and 5, the indicator 30, Fig. 5, in the aircraft comprises a rotatable compass card 10 slaved to a gyro-compass 42, the aircraft heading being indicated by a fixed index 12. The pointers 14 and 16 are set in accordance with the relative bearings of the transmitters Tr and Tf respectively by means of automatic direction-finders 20, 32 and synchros 26, 38 so that the readings of the pointers 14 and 16 on the card 10 indicate the magnetic bearings of the transmitters Tr and Tf. Alternatively, the two pointers 14 and 16 may be controlled by a single direction-finder, Fig. 9 (not shown), tuned sequentially to the two transmitters. An index 18 controlled from the gyro-compass 42 via a differential 18b is set by adjustment of the manual input 18c to the differential to indicate the direction of the runway. A second similar indicator 30<SP>1</SP>, Fig. 5, controlled by the direction-finders 20, 32 and synchros 50, 58 is also provided but in this case the effects of atmospherics and transients is eliminated by applying the output from each direction-finder 20, 32 to its synchro 50, 58 through a low-pass filter 52, 62 and a rate sensor 54, 64 which during the presence of excessive signal variations, e.g. due to aircraft bank and roll, maintains the previous relatively stable signal level. When the aircraft is on its final approach path its lateral displacement from and longitudinal displacement along the runway are computed at 95 as functions of the outputs from the direction-finders 20, 32 and gyrocompass 42 and applied respectively to effect transverse deflection of a longitudinal runway bar 84 and a transverse runway bar 90 in the pilot's lateral deviation indicator 70 and copilot's longitudinal deviation indicator 72. The deflection sensitivities are controlled by switches 86b and 92b and the outputs from the computer 95 may be applied to a conventional flight director or automatic pilot. Each of these indicators 70 and 72 also comprises a compass card 74, 76 controlled by the compass 42, the orientations of the runway bars 84, 90 being fixed relative to the cards 74, 76 with the longitudinal runway bar 84 parallel to the runway bearing and the transverse runway bar 90 perpendicular to the runway bearing. On the indicator 70 the orientation of an aircraft image 84 and the angular position of an index 78 are controlled in accordance with the angular position of the pointer 14 in the indicator 30 so that in operation the index 78 and the aircraft image 84 are in alignment, Fig. 6 (not shown), and similarly on the indicator 72 the orientation of an aircraft image 94 and the angular position of an index 80 are controlled in accordance with the angular position of the pointer 16. Fig. 8 shows an arrangement of transmitters for two divergent runways 100, 102 which provides for landing in either direction on each runway, the transmitters Tf 1,2  and Tr 1,2  being common to the two landing systems. In operation the pilot homes on to the beacon Tf, flies over it away from the runway on a course parallel thereto by maintaining the pointer 16 in the indicator 30 coincident with the runway direction index 18 in a position substantially opposite to the fixed index 12, makes a 180 degrees turn to the left and then flies towards the runway along the extension of the centre line thereof by maintaining the pointer 14 in the indicator 30 coincident with the runway direction index 18, the drift angle being given by the angle between the fixed index 12 and the runway direction index 18. Fig. 4 (not shown) illustrates the successive appearances of the indicator 30 during such an operation and Figs. 6 and 7 (not shown) illustrate the corresponding appearances of the indicators 70 and 72, all the indicators being shown with the north direction on the compass card in a fixed direction, i.e. vertically upwards.