GB2140757A - Excessive descent rate warning system for tactical aircraft - Google Patents

Abstract

A system for providing an aural warning to the pilot of a tactical aircraft if, on approach, the sink rate of the aircraft is excessive for the altitude at which the aircraft is flying. The warning is given only when the landing gear is down and when any weapons carried are unarmed, and the airspeed is below 300 knots. The altitude/sink rate envelope in which a warning is given is as shown. <IMAGE>

Description

SPECIFICATION Excessive descent rate warning system for tactical aircraft BACKGROUND OF THE INVENTION Field of the Invention This invention relates generally to ground proximity warning systems, and more particu larly to a system that provides a warning to the pilot of a tactical aircraft, such as a fighter/attack aircraft, flying the approach leg of the flight if the descent rate of the aircraft is excessive for the altitude at which the aircraft is flying.

Description of the Prior Art Systems for providing the pivot of an aircraft with a warning in the event that the aircraft is descending too rapidly on approach are known. Typical of such systems are the systems disclosed in United States Patent Nos.

3,946,358, 3,947,808, 3,958,219 and 4,215,334, all assigned to the same assignee as the assignee of the present invention.

While all of the above systems serve the basic function of alerting a pilot if the descent rate of the aircraft exceeds a predetermined safe rate determined by the radio altitude of the aircraft, the above-described systems are designed to operate with transport aircraft, particularly with large, turbine powered aircraft of the type flown by commercial airlines.

Since such transport aircraft typically have flight profiles that are considerably different from those of a tactical aircraft, for example, a fighter/attack aircraft making a landing onto an aircraft carrier, systems designed for transport aircraft would not be effective on tactical aircraft since they would have a tendency to generate false warnings, thereby losing their effectiveness as pilots ignored the warnings.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a ground proximity warning system that overcomes many of the disadvantages of the prior art warning systems.

It is another object of the present invention to provide a warning system to the pilot of a tactical aircraft on approach if the sink rate of the aircraft is excessive for the altitude at which the aircraft is flying.

It is yet another object of the invention to provide a ground proximity warning system for alerting the pilot of a tactical aircraft if his descent rate on approach is dangerously high, with the warning criteria having been selected to match the operating procedure used with such tactical aircraft.

Briefly, in accordance with a preferred embodiment of the invention, there is provided a system that monitors the descent rate of the aircraft when the landing gear is down, the indicated airspeed is less than 300 knots and the, weapons are not armed, and issues an aural warning to the pilot if the barometric descent rate exceeds a predetermined safe limit for the radio altitude at which the aircraft is flying.

DESCRIPTION OF THE DRAWING These and other objects and advantages of the invention will become readily apparent upon consideration of the following detailed description and attached drawing wherein: Figure 1 is a logicai block diagram of the warning system according to the invention; and Figure 2 is a graph of the barometric descent rate required to generate a warning as a function of radio altitude.

DETAILED DESCRIPTION OF THE PRE FERRED EMBODIMENT Referring now to the drawing, with particular attention to Fig. 1, there is illustrated an embodiment of the ground proximity warning system according to the invention generally designated by the reference numeral 10. The system 10 according to the invention is illustrated in Fig. 1 in logical block diagram form as a series of gates, comparators and the like for purposes of illustration; however, it should be understood that the actual implementation of the logic can be other than as shown in Fig. 1, with various digital and analog implementations being possible. The signals used by the system as described include radio altitude, barometric altitude rate, airspeed and signals indicating the position of the landing gear and whether the weapons are armed, along with various validity signals.Depending on the type of aircraft in which the warning system is installed, the signals shown in Fig.

1 can be obtained from individual instruments such as a barometric altimeter 12, a barometric rate circuit 14, a radio altimeter 16, an airspeed signal source 1 8 such as an air data computer or airspeed indicator and various discrete elements indicating the position of the gear, whether the weapons are armed and whether there is weight on the wheels. Alternatively, the signals can be obtained from a digital data bus in certain newer aircraft.

Because this system is designed to be operative only during the approach to a landing phase of a flight profile, its operation is inhibited during other phases of flight in order to avoid the possible generation of false warnings during those phases. The inhibiting function is accomplished by a pair of AND gates 20 and 22 that monitor various flight conditions and the configuration of the aircraft to determine whether the aircraft is on an approach to a landing. Two of the parameters that are monitored by the gate 20 are whether the landing gear is down and whether there is any weight on the wheels. In addition, a signal indicating that the weapons are not armed is applied to the gate 20, because under normal landing conditions, the weapons would not be armed. If they were, this would indicate that the aircraft was operating in a phase other than an approach to a landing.In addition, the airspeed is monitored by a comparator 24 which provides a signal to the AND gate 20 when the airspeed is below 300 knots indicating a probable landing condition.

Also, signals indicating that the radio altitude signal and the barometric altimeter signals are not inhibited are applied to the AND gate 22 in order to prevent the generation of warnings in the event of a faulty barometric or radio altimeter.

In addition, in order further to reduce the probability of false warnings, the system is inhibited below 50 feet of radio altitude and above 1,000 feet of radio altitude by a comparator circuit 26 that is responsive to signals from the radio altimeter 1 6 and provides enabling signals to the AND gate 22 only when the aircraft is between 50 feet and 1,000 of radio altitude.

If all of the above conditions are met, the AND gate 22 is enabled and placed under the control of an OR gate 28 controlled by a pair of comparators 30 and 32. The comparators 30 and 32 are responsive to the radio altitude and barometric rate signals, and apply a signal to the OR gate 28 when the sink rate is excessive for a given radio altitude. Upon receipt of a signal from the OR gate 30 or the OR gate 32, the gate 28 causes the gate 22 to apply a warning initiation signal to a warning circuit such as a digital voice warning generator 34. This causes the warning generator 34 to generate a digitally synthesized voice signal, such as, the words "SINK RATE", and apply them, either directly or indirectly, to a transducer 36, which may be a loudspeaker, or an earphone or the like.

In the illustrated embodiment, two comparators 30 and 32 are utilized to determine the barometric rate versus radio altitude relationship required to generate a "SINK RATE" warning, but a signal comparator can also be used. However, because of the particular shape of the warning curve illustrated in Fig.

2, it has been found convenient to utilize two separate comparators. The comparator 30 is used to initiate warnings for low radio altitudes and descent rates below 3,000 feet per minute, while the comparator 32 is used to initiate warnings for descent rates in excess of 3,000 feet per minute. Thus, the comparator 32 monitors the signal from the barometric rate circuit 14, and compares it with a reference signal representative of a 3,000 feet per minute descent rate that is applied to the other terminal of the comparator 32. Whenever the signal from the rate circuit 14 exceeds the reference signal representative of a 3,000 feet per minute descent rate, the comparator 32 applies a signal to the OR gate 28.

This signal causes the OR gate 28 to enable the AND gate 22, and causes a warning to be generated. For descent rates below 3,000 feet per minute, the comparator 30 controls, and causes the warning to be generated as a function of both the barometric descent rate and the radio altitude in accordance with the two-step curve below a radio altitude of 600 feet radio altitude and a 3,000 feet per minute descent rate shown in Fig. 2. Typically, the "SINK RATE" warning will be generated when the descent rate exceeds 3,000 feet per minute at 600 feet of radio altitude, when it exceeds 2,500 feet per minute at 200 feet of radio altitude, and when it exceeds 1,250 feet per minute at a radio altitude of 50 feet.

The above-described relationship between the barometric altitude rate and the radio altitude required to generate a warning is illustrated in greater detail in Fig. 2. The shaded area beneath the graph of Fig. 2 illustrates the various relationships between descent rate and radio altitude values that cause the warning, "SINK RATE", to be generated. This warning envelope has been determined by the flight characteristics of fighter/attack bombers such as, the Fairchild A10, and from the manner in which such aircraft are operated during the landing phase of the flight. Because such aircraft often fly at relatively low levels and may encounter relatively high descent rates during such low level flight, the top of the envolope of Fig. 2 is limited at 1,000 feet to avoid false warnings during maneuvering above 1 ,000 feet. This results in a considerably different envelope than the envelope utilized for transport aircraft which permits warnings up to an altitude of approximately 2,450 feet. Moreover, the descent rates permitted at lower altitudes are substantially greater for the tactical aircraft than for transport aircraft. For example, in the warning envelope illustrated in Fig. 2, a descent rate of up to 2,500 feet per minute is permitted at an altitude of 200 feet, while a warning system used in a transport aircraft would generate a warning at approximately one-half of that rate of descent. However, below 200 feet, the permitted descent rate is rapidly reduced to approximately 1,500 feet per minute at an altitude of 50 feet above ground to avoid excessively high descent rate touchdowns.

Claims (21)

1. A warning system for providing a warning to the pilot of an aircraft on an approach to a landing in the event that the aircraft is descending too rapidly, comprising: means responsive to signals representative of the altitude of the aircraft above ground, the descent rate of the aircraft and the position of the landing gear for generating a warning if the aircraft is below approximately 1,000 feet above ground and has a descent rate in excess of approximately 3,000 feet per minute.

2. A warning system as recited in claim 1 wherein said altitude and descent rate signal responsive means further includes means for generating said warning at descent rates lower than approximately 3,000 feet per minute when said aircraft is below approximately 600 feet above the ground.

3. A warning system as recited in claim 2 wherein said lower descent rate warning generating means includes means for generating said warning when the descent rate exceeds approximately 2,500 feet per minute at an altitude of approximately 200 feet above ground, wherein the descent rate necessary to generate the warning increases with altitude above ground until a descent rate, of approximately 3,000 feet per minute is required to generate the warning at an altitude of approximately 600 feet above ground.

4. A warning system as recited in claim 3 wherein said lower descent rate warning generating means further includes means for generating said warning when the descent rate exceeds approximately 1,500 feet per minute at an altitude of approximately 50 feet above the ground, wherein said descent rate necessary to generate the warning increases with altitude above ground until a descent rate of approximately 2,500 feet per minute is required to generate the warning at an altitude of approximately 200 feet above ground.

5. A warning system as recited in claim 4 wherein said descent rate increases linearly with altitude between 50 and 200 feet above ground and between 200 and 600 feet above ground.

6. A warning system as recited in claim 1 further including means for inhibiting the generation of the warning when the altitude of the aircraft is less than approximately 50 feet above the ground.

7. A warning system as recited in claim 1 further including means responsive to a signal representative of the airspeed of the airspeed for enabling the generation of said warning only when the airspeed is below a predetermined airspeed.

8. A warning system as recited in claim 7 wherein said predetermined airspeed is approximately 300 knots.

9. A warning system as recited in claim 1 wherein said aircraft is fitted with weapons, and wherein said warning system includes means responsive to the arming of the weapons of the aircraft for enabling the generation of said warning only when the weapons are not armed.

1 0. A warning system as recited in claim 1 wherein said aircraft is fitted with retractable landing gear, and wherein said warning system includes means responsive to a signal representåtive of the position of the landing gear for enabling the generation of said warning only when the landing gear is down.

11. A warning system for providing a warning to the pilot of an aircraft on an approach to a landing in the event that the aircraft is descending too rapidly, comprising: means for providing a signal representative of the airspeed of the aircraft; means for providing a signal representative of the descent rate of the aircraft; means for providing a signal representative of the altitude above ground of the aircraft; and means responsive to said airspeed signal providing means, said descent rate signal providing means and said altitu.de above ground signal providing means for generating a warning if the aircraft is flying below a predetermined airspeed, and has a descent rate in excess of a predetermined rate determined by the altitude above ground of the aircraft.

1 2. A warning system as recited in claim 11 wherein said predetermined airspeed is approximately 300 knots.

1 3. A warning system as recited in claim 11 wherein said system includes means for providing a signal representative of the position of the landing gear of the aircraft, wherein said system is responsive to the aircraft position signal providing means for enabling the generation of said warning only when the landing gear is down.

14. A warning system as recited in claim 11 wherein said warning generating means further includes means for generating a warning at descent rates greater than approximately 3,000 feet per minute when said aircraft is below approximately 600 feet above the ground.

1 5. A warning system as recited in claim 14 wherein said warning generating means further includes means for generating said warning when the descent rate exceeds approximately 2,500 feet per minute at an altitude of approximately 200 feet above ground, wherein the descent rate necessary to generate the warning increases with altitude above ground until a descent rate of approximately 3,000 feet per minute is required to generate the warning at an altitude of approximately 600 feet above ground.

16. A warning system as recited in claim 1 5 wherein said warning generating means further includes means for generating said warning when the descent rate exceeds approximately 1,500 feet per minute at an altitude of approximately 50 feet above ground, wherein said descent rate necessary to generate the warning increases with altitude above ground until a descent rate of approximately 2,500 feet per minute is required to generate the warning at an altitude of approximately 200 feet above ground.

1 7. A warning system as recited in claim 1 6 wherein said warning generating means further includes means for increasing the de scent rate necessary to generate a warning linearly with altitudes between approximately 50 and 200 feet above ground and between approximately 200 and 600 feet above ground.

1 8. A warning system as recited in claim 11 further including means for inhibiting the generation of a warning when the altitude of the aircraft is less than approximately 50 feet above the ground.

1 9. A warning system as recited in claim 11 wherein said aircraft is fitted with weapons, and said system includes means for sensing the arming of the weapons, said system further including means responsive to the arming of the weapons of the aircraft for permitting said warning to be generated only when the weapons are not armed.

20. A warning system as recited in claim 11 wherein said descent rate signal providing means includes means for providing a signal representative of the barometric descent rate.

21. A warning system for providing a warning to the pilot of an aircraft on an approach to a landing when the aircraft is descending too rapidly, substantially as described herein with reference to the drawings.