CA1125418A

CA1125418A - Terrain clearance warning system for aircraft

Info

Publication number: CA1125418A
Application number: CA274,459A
Authority: CA
Inventors: Charles D. Bateman
Original assignee: Sundstrand Data Control Inc
Current assignee: Sundstrand Data Control Inc
Priority date: 1976-07-19
Filing date: 1977-03-17
Publication date: 1982-06-08
Also published as: DE2732646A1; AU504133B2; GB1535488A; DE2732646C2; AU2379277A; SE420820B; IT1079327B; US4030065A; JPS5311498A; FR2359396A1; FR2359396B1; JPS6013124B2; SE7707871L

Abstract

ABSTRACT OF THE DISCLOSURE
By utilizing a radio altimeter in junction with a measure of the aircraft speed, landing gear position and position, an aircraft terrain warning system is made possible which provided a voice warning indicating that the aircraft is too low with the respect to the terrain when the aircraft is above a predetermined speed. For aircraft speeds below the predetermined speed, a voice warning is provided when the aircraft is below predetermined altitude withthe landing gear up indicating that the aircraft is too low with the gear up andwhen the gear is down and the flaps are not in a landing position and the aircraft descends below a second predetermined altitude a voice warning is gen-erated indicating that the aircraft is too low with flaps up.

Description

1125~113 _CI~GROVND OF T~E INVENTION
s The invention relates to the field of aircraft ground proxim~ty warnihg systems and more particularly to systems providing warning of insuffi-cient terrain clearance.
Prior art ground proximity warning systems, such as the terrain clear-ance system disclosed in Bateman U.S. Patent No. 3,946,358 and Bateman et al U.S. Patent No. 3,944,968, both of which are assigned to assignee of this appli-cation, utilized both landing gear and landing flap position signals combined with radio altitude signals to generate a warning in the event terrain clearanceis less than predetermined limits. These systems would have provided timely warnings for certain controlled flight into terrain incidents ~here the aircraftwas flown into the terrain when the aircraft was not in a landing configur2tion.However, there are instances where a pilot may extend the landing gear to act asB an aerodynamic brake or drag during ccttain portions of a flight. Lowering the landing gear in the prior art ground proximity warning systems inhibits the terrain warning mode which has the effect of eliminating a terrain warning protection capability under certain circumstances when it in fact might be needed.
In addition, there have been instances in the past when the flight crew have misread the barometric altimeter by 10,000 feet and as a result have un-knowingly flown at cruising speed3 within a vcry close proximity to the ~round, ; The prior art terrain clearance warning systems, as represented in the 3,~46,358 patent, in many instances will not provide sufficient warning time at these higher cruise speeds. This is due in part to the fact that they do not provide a warning until the aircraft is within 200 feet of the ground unless it also is descending at a barometric descent rate at a rate great enough to raise the warning threshold to 600 feet.
A failure of the gear or flap switch utilized for a ground proximity warning system input can lead to a loss of confidence in the system since such a failure will mkmifest itself on a landing approach with a continuous pull-llp tl~ 6 /e~n warningO Sillce the cause of ~h-pr~b~m is not i~nediately obvious, pilots will tend to lose ~aith in the s~stem~

llZ5~

Another cause of lack of faith in ground proximity warning systems i9 the fact that heretofore the majority of the warnings have been in the nature of a single imperative command to pull-up. It has been discovered that pilots are reluctant to immediately respond with a maneuver when they are not certain what the circumstances are that have triggered the warning.

SUM~ ~ Y OF ~IE INVE~TION

It is therefore an obiect of the invention to provide a terrain warning system which will generate a voice warning indicating that the aircraft is too low for the terrain.
It is a further object of the invention to provide a terrain clearance warning system for aircraft wherein the warning criteria with respect to the proximity of terrain are varied as a function of aircraft speed and voice warn-ings are generated to indicate that the aircraft is too low with respect to the terrain.
It is another object o the invention to provide a terrain clearance warning system wherein a voice warning is provided to indicate thst the aircraft is ~oo low with respect to the terrain and, for certain aircraft speeds, that the aircraft is too low with the landing gear up.
It is still a further ob~ect of the invention to provide a terrain clearance warning system wherein voice warnings areprovided to i~dicate, depend-ing upon the aircrat's speed, that the aircraft is too low with respect to the - terrain or that the aircraft is too low with respect to the terrain or that the aircraft is too low with the flaps up.
It is yet another object of the in~ention to provide a terrain clearance wan-ing system wherein voice warnings are provided to indicate that the aircraft is too low with respect to the terrain wherein the altitude utilized to trigger this warning varies as a function of aircraft speed, and f.urther for aircraft speed6 below a predetermined value that the aircraft is too low with the gear up, or that the aircraft is too low with the flaps up.
The invention utilizes signals from a radio altimeter to determine the aircraft's actual altitude above the terrain In addition~ the aircrat uses a signal representing the aircraft's speed such as air speed or ~lach number ~1~5~

along with signals indicating whether the flaps and landing gear are up or down.
For example~ when the aircraft descends within 1000 feet of the ground at over a predetermined speed such as 045 Mach, a voice warning wil] be given indicating the aircraft is too low with respect to the terrain unless the landing gear and flaps are both lowered. In addition~ the altitude at which the terrain voice warning is given is varied as a function of aircraft speed in order to increase warning times during initial approach and descent and phases of operation. ~len the aircraft descends below 500 feet with the landing gear up below a predeter-mined speed such as .35 Mach a voice warning will be given indicating the air-craft is too low, gear. By the same token, when the flaps are not in a landingposition and the aircraft approaches within 200 ~eet of the gro~md with the land-ing gear down, a voice warning will be given that the aircraft is too low, flaps. -By utilizing the voice warnings indicating the conditions which gaverise to the warning, the pilot's confidence and acceptance of the system are ; significantly enhanced, thereby substantially increasing the effectiveness of the system in actual operating environments. Also, by increasing the altitude at which a terrain clearance warning can be generatea to 1000 feet when the aircraft is at cruise speed, unintended high speed flight near the ground can be avoided.

BRIEF DESCRIPTION OP THE D~WINGS

FIG. 1 is a graphical illustration oE tbe relationship between air-craft altitude and speed for generating a terrain clearance warning when the landing gear is up, FIG. 2 is a graphical illustration of the relationship between aircraft altitude and speed for generating a terrain clearance warning when the aircraft's flaps are up; and FIG. 3 i8 a functional block diagram for a circuit for imple~enting the warning curves of FIGS. 1 and 2.

- DETAILED DESCRIPTION OF THE IN~ENTION

ILI ~'IG. 1 of the dra~ngs is illustrated graphically ~he relationship 5~

between aircraft speed as represented in ~lach number and the aircraft's al~i-tude above grourd or generating a terrain clearance warning signal when the aircraft's landing gear is up. For example, whenever the aircraft has a speed of less than .35 Mach and descends within 500 feet of the terrain, a too low, gear voice warning will be given as indicated by the cross-hatched portion 10 of FIG 1. For aircraft speeds between .35 and .45 Mach, the warning boundary indicated by line 12 will be essentially dependent on the aircraft speed and the voice warning will indicate that the aircraft is too low with respect to the terrain~ In other words, for higher speeds the altitude at ~lich a warning will be given is also greater. For aircraft speeds in excess of .45 Mach, the too low, terrain voice warning will bé given any time the aircraft approaches within 1000 feet of ~he terrain as indicated by the cross-hatched portion 14 of FLG. 1.
Similarly, the graph in FIG. 2 illustrates the operation of the terrain clearance warning system when the landing gear is down but the flaps are not in a landing setting. The cross-hatched portion 16 of FIG. 2 indicates that a too low, flaps, voice warning will be given when the aircraft has a speed of less than .28 Mach and is within 200 feet of the terrain. When the aircraft has a speed of between .38 Mach and .45 Mach a too low, terrain warning will be

2~ given if the aircraft should descend below line 1~ for a given Mach number between .28 and .45. ~len the aircraft has a speed of greater than .45 Mach a too low, terrain warning will be given, as indicated by the c~ ss-hatched area 20 of FIG. 2, whenever the aircraft descends within 1000 feet of the terrainO
It is thus apparent from the characteristics illustrated in both FIGS. 1 and 2 that both the character and the altitude at which warnings are given are dependent upon the aircraft's speed~ In addition,the altitude and the character of tlle type warning given are also dependent upon the position of the landing gear and flaps. A comp~rison of the graphs in FIGS. 1 and 2 will also illustra~e the fact that when the aircraft is proceeding with a relative-ly high rate of speed, .45 ~lach or over, with both the landing gear up and t~e flaps up a terrain warning is gi~-en for relatively high altitudes thereby providing timely warning in cases ~here the aircraft is inadvertently ~y'iug at cruise - ~t -5~1~

speeds near ~he ground.
A functional block diagram for implementing the terrain warning system having the characteristics illustrated in the graphs of ~IGS. 1 and 2 is presented in FIG 3. In the preferred embodiment of the invention as illus-trated in FIG. 3, a digital memory 22 contains the sequence of bits required to form a word. A digital to analog converter 24 receives the bits from memory 22 over line 26 and converts the bit stream into an analog signal which in turn is transmitted over line 28 to an amplifier 30. The amplified analog signal is transmitted over line 32 to a speaker 34 for the production of the appropriate words. The bits contained in the memory are selected for transmis~ion to the digital analog converter 24 by means of a memory address logic 36. A similar voice generating system is disclosed in Batel~n U.S. Patent No. 3,925,751. The memor~ address logic 32 inturn is controlled by a plurality oE inputs 40,42,44, and 46 which indicate that portions of the digital memory 22 should be selected to form the words "terrain," "gear," "flaps" and lltoo low" respectively. The memory address logic 36 is inhibited by means of a signal transmitted over line 48 from an AND gate 50. When the signal GD meaning the landin gear is down is app~ied over line 52 to AND gate 50 ~nd a signal FD indicating that the flaps are down or in a landing position is transmitted over line 54 an inhibit signal will be transmitted over line 48 to the memory address logic to prevent the generation of any terrain clearance warnings. Thus, there will be no terrain clearance warnings when the landing gear is down and the flaps are in a landing settlng.
A signal representing aircraft speèd is applied over a line 57 from a Mach meter 58 or similar device to a function generator 60. The function gen-erator 60 applies a signal to a positive terminal of a summing junction 62 over line 64 wherein the signal on line 64 will be scaled to represent 200 feet for .28 Mach or less, between 200 and 500 feet for speeds between .28 and .35 Mach, `

and between 500 and 1000 feet for speeds between .35 and .45 ~lach. For all speeds greater than .45 ~ach~ the output of the function generator will be a sig-nal that represents 1000 feet~ A radio altimeter 66 provides an altitude signalhR which is used as an input to another positive terminal o~ the summing junction 62. A comparator 68 rece~ves the output from the summing junction 62 over line 70, and generates a high or positive logic signal on line 72 ~hen the air-craft is below a desired altitude wherein either one or the other or both of the gear and ~laps are up tnereby immediately initiating the generation of the words "too low." A positive logic signal on line 72 will also serve to enable each of a plurality of gates including 7~, 76 and -/8 which control the initiating of signals over lines 40, 42, 4~" and 46 that in turn result in generating the desired words by means of memory address logic 36.
A comparator circuit 80 connected to line 56 generates a positive logic signal on line 82 when the aircraft's speed is greater than .35 ~lach. In the event that the landing gear is up indicated by means of a positive signal applied to line 84, an ~ND gate 86 having both lines 82 and 84 as inputs will transmit a positive logic signal over line 86 to an OR gate 88. The OR gate 88 will transmit the positive signal on line 86 to a second input terminal on AND
gate 78 thereby cooperating with the positive signal on line 72 to initiate the generation of the woxd '~terrain." This operation of the circuit in FIG. 3 would correspond to line 12 in the graph of FIG. 1. A positive signal on line 86 which indicates that the aircraft speed is above .35 Mach will be applied by n~eans of an inverter terminal to AND gate 76 thereby having the effect of inhibiting the generation of the word "gear." Thus as it can be seen from FIG, l for any aircraft speeds of over .35 Mach, the word "gear" will not be generated.
In the event that the alrcraft's speed is grea~er than .28 Mach as measured by a comparator circuit 90, and the aircraft's flaps are not in a land-ing s~tting, as indicated by a positive logic signal on line 92, an A~D gate 94 will generate~a positive logic signal on line 96. A positive logic signal on line ~6 will be transmitted through the OR gate 88 to the ~D gate 78 thereby initiating the generation of the word "terrain." By the same token, a positive logic signal on line 96 as input through an inverting input to AND gate 74 will `
tend to inhibit the generation of the word "flaps." The operation of this portion of the logic circuitry can be seen to relate to the portion indicated by line 18 of the graph of FIG. 2, When the aircraft has a speed of less than .35 Mach with the landing gear up, corre~ponding to the portion 10 of the graph in FIG. l, line 82 will i~l2~8 have a low logic signal thereon thereby producing a low signal on line 86 thus tending to inhibit the generation of the word "terrain." However, the high signal on line 84 will cooperate with a low signal on line 8 to generate the word "gear" by means of AND gate 76. Thus, for aircraft speeds below .35 ~lach, the too low gear warning will be generated.
In the event that the aircraft has a speed of less tllan .28 ~lach, the comparator 90 will generate a low signal thus tending to turn o~f gate 9~ and producing a low signal on line 96. This will cooperate with a similar low signal on line 86 to inhibit the AND gate 78 thereby preventing the generation of the w ord "terrain." Assuming the landing gear is down, a high signal on line 9~ will cause the generation of the word "flaps." In the event that the gear is not down, a high signal on line 84 will inhibit gate 74 and thus the generation of the word '~flaps.~' Thus it is apparent from the connection oE line 84 to gate 74 that the word "gear" has priority over the word "flaps" in the event they are both not down.
Elements 48 through 96 represent an electronic analog computer circuit for controlling the generation of the various voice warnings as a function of altitude, speed, flap and gear setting. Although the preferred embodiment of the invention utilizes analog computer logic, a digital computer could be used to perform the same functions.
The voice 9ignals generated~ such as "too low~ terrain," "too lo~, gear" and "too low, flaps" are the preferred words to be used in the system disclosed herein. However, it is not intended that the invention be limited to these words and the words are used in the specification and claims to describe in a generic sense the nature of the information being transmitted to the pilot, ~ikewise, the various values for the curves of FIGS. 1 and 2 and the values of the circuit elements of FIG. 3 are intended to illustrate the preferred embodi-ment of the invention and would most likely take on somewhat different values for dlfferent operating environments and aircraft types.

-7~

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A terrain clearance warning system for aircraft comprising:
a radar altimeter for generating signals representing the aircraft's altitude above the terrain;
a source of signals representing the aircraft's speed;
a source of signals representing the position of air-craft landing gear;
means, responsive to said speed signal, for generating a reference altitude signal as a function of aircraft speed;
means, responsive to said altitude signals and said reference altitude signals, for comparing aircraft altitude above terrain with said reference altitude signal;
means, responsive to said landing gear signal and speed signal and said comparing means for generating a first type of warning signal when the aircraft has descended below a first predetermined altitude below a predetermined speed with the landing gear up, and means, responsive to said landing gear signal, said speed signal and said comparing means for generating a second type of warning signal when the aircraft has descended below a second predetermined altitude above said predetermined speed with the landing gear up.

2. The system of claim 1 wherein said first warning signal means includes means for generating a too low, gear voice signal.

3. The system of claim 2 wherein said second warning signal means includes means for generating a too low, terrain voice signal.

4. The system of claim 3 wherein said second warning signal means caries, as a function of speed, the value of said second predetermined altitude.

5. A terrain clearance warning system for aircraft com-prising:
a digital memory;
a digital to analog converter circuit operatively connected to said digital memory;
a speaker operatively connected to said digital to analog converter;
a memory address logic circuit operatively connected to said digital memory effective to selectively output from said digital memory groups of predetermined information bits;
a source of signals representing aircraft speed;
a radio altimeter for generating a signal representing the aircraft's altitude above ground;
a source of signals representing the position of the aircraft landing gear;
a source of signals representing the position of the aircraft's flaps;
an electronic computer responsive to said speed, altitude, flap and landing gear signals and operatively con-nected to said memory address logic, effective to cause the generation of a first type of voice signal when the aircraft has descended below a first predetermined altitude below a first predetermined speed with the landing gear down, and a second type of voice signal when the aircraft has descended below a second predetermined altitude above said first predetermined speed.

6. The system of claim 5 wherein said electronic com-puter is additionally effective to cause the generation of a third type of voice signal when the aircraft has descended below a third predetermined altitude below a second predetermined speed with the flaps down.

7. The system of claim 6 wherein said electronic com-puter is additionally effective to inhibit said third voice signal when said first voice signal has been generated.

8. The system of claim 7 wherein said said first voice signal is a too low, gear signal; said voice second signal is a too low, terrain signal and said third voice signal is a too low, flaps signal.

9. The system of claim 8 wherein said electronic com-puter is an analog computer.

10. The system of claim 7 wherein said electronic analog computer includes a function generator circuit responsive to said speed signal for generating a scaled signal which is functionally related to speed.

11. The system of claim 10 wherein said electronic analog computer includes a comparator circuit which is operatively connected to said function generator and responsive to said altitude signal for generating a logic signal indicating air-craft descent below a predetermined value of altitude wherein said predetermined value is a function of speed.

12. A terrain clearance warning system for aircraft comprising:
a source of signals representing the aircraft's altitude above the terrain;
a source of signals representing the aircraft's speed;

Claim 12 continued....

a source of signals representing the position of the aircraft's landing gear; and computer means, responsive to said altitude signal said speed signal and said landing gear signal, for generating a too low, terrain voice warning when the aircraft is below a first predetermined altitude above the terrain and generating a too low, gear voice warning when the landing gear is up, below a predetermined speed.

13. The system of claim 12 wherein said computer means generates said too low, gear voice warning only below a second predetermined altitude.

14. The system of claim 12 wherein said first predetermined altitude is approximately 1,000 feet above the terrain.

15. The system of claim 12 wherein said second pre-determined altitude is approximately 500 feet above the terrain.

16. The system of claim 12 wherein said computer means includes means for increasing the value of said first pre-determined altitude as a function of speed.

17. The system of claim 13 wherein said computer means includes means for increasing the value of said first predetermined altitude as a function of speed.

18. The system of claim 17 wherein the value of said first predetermined altitude is equal to said second predetermined altitude at said predetermined speed and the value of said first predetermined altitude is increased as a linear function of increasing speed.

19. The system of claim 18 wherein said means for increasing the value of said first predetermined altitude includes means for limiting said first predetermined altitude to a maximum value fox speeds greater than a second predetermined speed.

20. The system of claim 19 wherein said maximum value is approximately 1,000 feet.

21. The system of claim 19 wherein said second predeter-mined speed is approximately 0.45 Mach.

22. The system of claim 12 additionally including a source of signals representing the aircraft's flap position and where-in said computer means includes means for generating a too low, flaps voice warning below a third predetermined altitude when the landing gear is down and the flaps are not in a landing position.

23. The system of claim 22 wherein said third predetermined altitude is approximately 200 feet.

24. The system of claim 22 wherein said computer means includes means for inhibiting said too low, flap voice warning above a second predetermined speed.

25. The system of claim 24 wherein said second predeter-mined speed is approximately 0.28 Mach.

26. The system of claim 24 wherein said computer means includes means for generating said too low, gear voice warning only when the landing gear is up and the aircraft is below said first predetermined speed.

27. The system of claim 26 wherein said first predetermined speed is approximately 0.35 Mach.

28. The system of claim 25 wherein said computer means includes means, responsive to said landing gear signal, for inhibiting said too low, flap signal when the landing gear is up.

29. The system of claim 24 wherein said computer means includes means for increasing the value of said first predeter-mined altitude as a function of increasing the aircraft speed.

30. The system of claim 29 wherein the value of said first predetermined altitude is equal to said third predetermined altitude at said first predetermined speed and the value of said first predetermined altitude to a maximum value at a third predetermined speed.

31. The system of claim 30 wherein said third predetermined speed is 0.45 Mach.

32. The system of claim 30 wherein said maximum value is 1,000 feet above the terrain.