Patent GB-1488744-A (GB)
Title: Aircraft landing approach ground proximity warning instrument
IPC: G08B21/00
Filed: 1975-06-19
Abstract: 1488744 Radio navigation SUNDSTRAND DATA CONTROL Inc 19 June 1975 [19 June 1974] 26061/75 Heading H4D [Also in Division B7] An aircraft, provided with barometric altimeter 20, Fig. 2, radio altimeter 26 and glide slope receiver 37 is protected by a hazardous situation warning system giving warnings of the following situations: (a) Negative climb rate after take-off (b) Below minimum terrain clearance (c) Excessive sink rate (d) Excessive closure rate (e) Below glide slope The claims relate to the detection of and warning of the below glide slope hazardous situation. The several hazardous situations are detected in the following manner: (a) Negative climb-rate And gate 57, Fig. 3, produces the warning when five input conditions are valid: (1) The negative climb (drop) rate h B  is greater than 100 ft. p.m. as indicated by threshold bi-stable 56 (going 0 to 1 for |h B | >100, 1 to 0 for |h B | <50.) and using the h B  signal as produced from barometric altimeter (20) output h B  by differentiator 21, low attitude disabler (h R <50 ft.) 22 and filter 24, (2) The flaps are not down (inhibiting input), as indicated by an absence of an FD signal from landing flaps controlled gate 44. (3) The radio altitude h R  is less than 700 ft., and indicated by threshold bi-stable 30 fed by the radio altimeter 26. (4) The system is not in a test configuration. (5) The system is in a take-off configuration, as indicated by a T0 signal from bi-stable 58. (b) Below minimum terrain clearance And gate 62 produces the warning when three input conditions are valid: (1) The system is in a cruising, not a take-off configuration as indicated by #T0 from bi-stable 58. (2) The flaps are down, or the A/C is in a landing configuration as indicated by an absence of an FD signal. (3) The A/C is below minimum terrain clearance altitude, i.e. 480 ft. as indicated by threshold bi-stable 61 fed by a signal (h R  - 480) from junction 60. Circuit 66.67-68-64-63 makes the warning dependent on rate of descent and state of landing gear. This allows a "go around" turn, i.e. descent to below 480 ft., with landing geardown, intending to land, then landing gear up for a circle to "try again" without 61 giving a 1 and the terrain clearance alarm being given. (c) Excessive sink rate AND gate 70 produces the warning when three input conditions are valid: (1) The sink rate is excessive, the equation for the closure rate being at the output of junction 73, K(1300 - h B )th R . 74 is a threshold bistable. The inclusion of h R  in the equation makes the warning dependent on the altitude. (2) The system is not in a test configuration. (3) The altitude is less than 2450 ft. Above this height the closure equation is invalid. (d) Closure rate The operation of this part of the system is as in Specification 1,352,531 except that the boundary conditions of the warning function (Fig. 7, not shown) are here linear as against square. (e) Below glide slope And gate 86 produces the warning when six input conditions are valid: (1) The landing gear is not up (no GU signal). (2) The radar altitude h R . is below 700 ft, but (3) above 50 ft.  (4) The front course, Fig. 9, is being flown. (5) The A/C is below the glide slope as indicated by threshold bi-stable 87. At altitudes h R >150 ft. (88, 98) a glide slope deviation >1À6 slots is necessary to cause bi-stable 87 to give a 1 output. At altitudes between 50 and 150 ft. the sensitivity of 87 is reduced so that at 50 ft. a deviation of 3À0 dots is necessary. For h R <50 ft. no 1 output is possible and input (3) above inhibits anyway. (6) The A/C is intercepting and/or passing down the major lobe. This is indicated by a "G/S valid" signal from gate 85 fed for at least 15 secs, by a signal from AND gate 97 receiving in turn an absence of noise or side lobe indicating signal from band pass filter assembly 93, 94 and threshold assembly 95, 96-and a signal indicating a low valve or rate of change of deviation, i.e. the input to filter 101 is where h D 3 is the predetermined rate of change of barometric altitude for the 3 glide slope.