GB2175264A - System for alerting a pilot of a dangerous flight profile during low level manoeuvering - Google Patents

Abstract

A system that warns the pilot of an aircraft performing low level maneuvers of a dangerous flight profile monitors the altitude of the aircraft above ground, the roll angle and the descent rate of the aircraft to provide a specific warning if the descent rate of the aircraft exceeds a predetermined rate determined by the roll angle of the aircraft. This warning may be disabled if the aircraft is above a predetermined altitude above ground. <IMAGE>

Description

SPECIFICATION

System for alterting a pilot of a dangerous flight profile during low level maneuvering DESCRIPTION

Background of the invention Field of the invention

This invention relates generally to ground proximity warning systems, and more particularly to a system that protects an aircraft during low altitude maneuvers if the aircraft exceeds a predertermined descent rate while performing turning maneuvers or other maneuvers requiring a roll. A distinct specific warning is given in order to inform the pilot of the specific action that must be taken to recover from a dangerous flight profile.

Description of the prior art

Ground proximity warning system that warn a pilot of a dangerous flight profile are known. These systems provide warnings to the pilot of an aircraft under various unsafe flying conditions including flying below a preset minimum altitude, and permitting the aircraftto attain an excessive descent rate after take-off or on approach. An example of a system that provides a pilot with a warning if he drops below a predetermined minimum desired al- titude is a system that compares the radio altitude with the minimum decision altitude setting, or "bug" setting on the radio altimeter, and provides an aural or visual warning if the radio altitude drops below the set minimum decision altitude.

Examples of systems that provide a warning to a pilot during a take-off or a missed approach phase of operation if the aircraft should descent at an exvessive barometric rate or lose a predetermined amount of barometric altitude are disclosed in United States Patent Nos 3,936,358; 3,947,808; 3,947,810 and 4,319,218, assigned to the same assignee as the present invention.

While these system servo to provide the pilot with a warning in the event that the aircraft drops below a preset minimum desired altitude above ground, or if the aircraft descends excessively after take-off or a missed approach, such systems are designed primarily for transport aircraft that do not normally fly at low altitudes or execute turns or other severe or violent maneuvers near the 115 ground. Consequently, such systems would not normally provide adequate warning to the pilot of a highly maneuverable aircraft such as, for example, a fighter/attack aircraft executing tactical ma- neuvers near the ground.

Summary of the invention

Accordingly, it is an object of the present invention to provide a warning system that overcomes many of the disadvantages of the prior art warning 125 systems during high speed, low level maneuvering phases of aircraft operation, and in particular to provide the pilot of an aircraft executing turning and banking maneuvers near the ground with a warning of a dangerous condition such as an ex- GB 2 175 264 A 1 cessive descent rate in sufficient time to permit the pilot to take corrective action.

The invention may also provide a warning of an excessive radio altitude loss during take-off into rising terrain.

The mission flight profile of a fighter/attack aircraft contains low altitude cruise and attack segments, and if the pilot becomes distracted or disoriented, there is a danger of inadvertent de- scent into terrain or flight into slowly rising terrain. The danger of flying into rising terrain exists primarily during take-off, and during low altitude cruise. The danger of inadvertent descent is greatest during low level maneuvers requiring high roll angles, such as are encountered during an attack portion of a flight, because the pilot can easily become distracted and disoriented during such maneuvers, and because aircraft tend to sink when they are subjected to high roll angles. 85 The invention provides a system for providing a warning to the pilot of an aircraft maneuvering near the ground comprising; means responsive to a signal representative of the roll angle of the aircraft and to a signal repre- sentative of the descent rate of the aircraft for generating a warning to the pilot when the combination of roll angle and descent rate exceeds a predetermined level.

The system monitors the roll angle of the aircraft and preferably generates its specific warning in the event that the aircraft is below a second predetermined altitude, and exceeds a predertermined descent rate which varies as a function of the roll angle of the aircraft in order to warn the pilot that the aircraft is descending at an excessively high rate during a roll maneuver. The warning given should be specific enough to enable the pilot to diagnose the problem quickly, and in the present embodiment, a warning such as the warning "ROLL OUT" or similar term is provided. This system is preferably used in combination with the warning system described and claimed in GB No. 2139588A from which this Application is divided. The resulting combination generates two specific warnings to the pilot identifying the different dan- gerous flight profiles that might subsist.

DESCRIPTION OF THE DRAWINGS

Figure 1 is a logical block diagram of the warn ing system according to the invention; Figure 2 is a graph illustrating the relationship between airspeed and radio altitude where warn ings may be generated; and Figure 3 is a graph showing the relationship be tween barometric altitude rate and roll angle re quired to generate a warning that the aircraft is descending at an excessive rate during a roll ma neuver.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawing, with particular at- tention to Figure 1, there is illustrated an embodi- 2 GB 2 175 264 A 2 ment of a ground proximity warning system aG cording to the invention particularly useful for pro viding warnings of unsafe flight conditions during low level maneuvering generally designated by the reference numeral 10. The system 10 according to the invention is illustrated in Figure 1 in functional or logical block diagram form as a series of gates, comparators, flip-flops 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 Figure 1, with various digital and analog implementations being possible. The sig nals used by the warning system as described in clude radio altitude, barometric altitude rate, airspeed, engine RPM, roll angle of the aircraft, the 80 minimum decision altitude and signals indicating the position of the aircraft landing gear along with various validity signals. Depending on the type of aircraft in which the warning system is installed, the signals shown in Figure 1, can be obtained from individual instruments such as a barometric altimeter 12, a barometric altitude rate circuit 14, a radio altimeter 16 and a gyroscopic platform 18, as well as various discrete circuit elements such as a discrete element indicating the position of the landing gear. These signals may also be obtained from a digital data bus in certain newer aircraft.

As previously stated, the system according to the invention is designed to provide different warnings during different phases of aircraft operation. For 95 example, the system is designed to provide a first warning, such as, for example, an aural or voice warning "TOO LOW' should the aircraft descent below the minimum decision altitude during low level cruise. The warning will also be generated if 100 the aircraft should lose a predetermined percent age of the altitude attained after take-off, but prior to reaching the minimum decision altitude. In addi tion, the system is designed to provide a second specific warning, such as, for example, the aural or 105 voice signal "ROLL OUT" should the aircraft de scend too rapidly during a roll maneuver. Conse quently, logic circuitry is provided to indicate to the system the particular flight phase in which the aircraft is operating, i.e., take-off, low level cruise 110 or low level manuevering so that the appropriate warning will be generated should certain flight pa rameters be exceeded. This function is provided by the logic circuitry including AND gates 20, 22, 24, 26, and 28, an OR gate 30, a pair of settreset flip/ 115 flops 32 and 34, a transition detector 36 and a switch 38 controlled by the flip-flop 34.

Because the system is designed to be opera tional to provide warnings during take-off, low level cruise and low level maneuvering phases of 120 flight, certain determinations must be made to de termine whether the aircraft is indeed in one of the aforementioned phases. The initial determinations are made by the AND gate 20 which provides an enabling signal to the AND gates 22 and 24 only if 125 certain conditions are met. These conditions are that there is no weight on the wheels, indicating that the aircraft is actually flying, that the gear is up and the aircraft is not flying slower than 200 knots, thereby indicating that the aircraft is not in a 130 landing configuration. Also, for the system to be operational, the barometric altimeter 12, the barometric rate circuit 14 and the radio altimeter must be operating properly. Consequently, signals indi- cating that the barometric altimeter and radio altimeter have not been inhibited, as well as a signal indicating that the rate of the radio altitude is not excessive are applied to the gate 20 to cause the gate 20 to enable the gates 22 and 24 only if the signals from the barometric altimeter 12, the barometric rate circuit 14 and the radio altimeter 16 are valid.

In addition to determining whether the aircraft is flying in a configuration other than a landing configuration and that the instruments are operating properly, it is necessary to determine whether the aircraft is in an approach phase, or in a take-off or a go-around after missed approach phase. This determination is made by the gates AND 26 anbd 28, the OR gate 30 and the set/reset flip-flop 32. In the implementation shown, a take-off or a go-around after a missed approach is indicated only if both the conditions that take-off power is present and that the landing gear is up are met. If both condi- tions are met, the set/reset flip-flop 32 is reset. Signals indicative of take-off power that are applied to the gate 26 can be obtained from various sources, for example, from a comparator circuit that provides an enabling signal to the gate 26 when the RPM of the engine is sufficiently high to indicate take-off power, of from a discrete element indicating throttle position. An engine tachometer, which indicates for example, the RPM of the primary compressor of a jet engine, can be used to provide the engine RPM signal, and a predetermined RPM, for example, 90% of maximum engine RPM, can be used to indicate take-off power. The gear up signal can readily be obtained from another discrete element, such as, from a switch operated by the landing gear or by the landing gear control handle in the cockpit.

An approach condition is indicated by the gates 30 and 28 when the gear is not up of the aircraft is below 100 feet (30.5 metres) and the engine is not producing take-off power and the speed of the aircraft is below 200 knots (103 metres per second). An approach condition indication from the gate 28 serves to set the flip-flop 32.

In operation, during the take-off phase of flight, the set/reset flipflop 32 is reset, thereby causing the Q output of the flip-flop 32 to change from a high state to a low state. This transition is detected by the transistion detector 36 which generates an output pulse in response to the transition and sets a set/reset flip-flop 34. This causes the Q output of the flip-flop 34 to operate the switch 38 to the position shown in Figure 1,thereby to connect one input of the gate 22 to circuitry including a too low comparator 40, a scaling circuit 42 and a radio altitude accumulator 44. These devices determine when a "TOO LOW'warning should be generated by a generator 46 during the take-off mode of operation.

After the aircraft has completed its take-off, as evidenced by the radio altitude exceeding the mini- 3 GB 2 175 264 A 3 mum decision altitude (MDA), and IVIDA compara tor 50 provides a signal indicating that the aircraft has exceeded the minimum decision altitude in or der to reset the input of the flip-flop 34, thereby re setting the flip-flop 34. When the flip-flop 34 is reset, the switch 38 is operated to disconnect the gate 22 from the too low comparator 40 and con nected to LESS THAN IVIDA output of the MDA comparator 50, thereby making the system respon sive to any descents below the minimum decision 75 altitude. Consequently, if the aircraft drops below the minimum decision altitude when in this mode, the warning generator 46 will generate the "TOO LOW" warning and apply it to the transducer 48.

As long as the altitude of the aircraft is below 80 the minimum decision altitude plus a prederter mined increment, such as, for example, 100 feet (30.5 metres), but not below the minimum decision altitude, the AND gate 24 is enabled by the corn parator 50 via the GREATER THAN IVIDA and LESS 85 THAN MDA + 100 FEET (30.5 METRES) signal ap plied to two of its inputs. When so enabled, the AND gate 24 is made responsive to a pair of com parators 52 and 54 to operate a second warning generator 56 which generates a second warning such as, for example, "FlOLL OL17' when the de scent rate of the aircraft exceeds a predetermined level for a given roll angle.

Discussing the operation in greater detail, as the aircraft takes off, the flip-flop 32 is reset, thereby causing the transition detector 36 to provide an output pulse to set the flip-flop 34 to thereby con nect the gate 22 to the comparator 40. The output pulse from the transition detector 36 also resets the radio altitude accumulator to zero, or to a pre determined low value setting, such as, for exam pie, 50 feet (15.3 metres). The radio altitude accumulator receives the altitude signals from the radio altimeter 16, and retains the highest altitude reached since take-off. This maximum value of ra dio altitude reached since take-off is applied to a scaling circuit which multi-plies by a scaling factor, for example, 75% and applies to the too low com parator 40 which controls the operation of the too low warning generator 46 during the take-off phase of operation.

The radio altimeter signal is also applied to the too low comparator 40, and as long as the radio al titude remains above the maximum radio altitude multiplied by the scaling factor, no warning is gen erated. However, if the radio altitude drops below the scaled maximum altitude, for example, below 75% of the maximum altitude reached during the flight, the comparator 40 will provide a signal to the gate 22. This signal will cause the gate 22 to provide a signal to the "TOO LOW" warning gen erator 46 and cause the generator 46 to generate the "TOO LOW" warning and apply it, either di rectly or indirectly, to the transducer 48, provided that the other input of the gate 22 is enabled by the gate 20.

The radio altitude signal from the altimeter 16 is also applied to the IVIDA comparator 50 which monitors the radio altitude signal from the radio altimeter 16 and provides a GREATER THAN MDA 130 signal to the flip-flop 24 when the radio altitude exceeds the minimum decision altitude. This signal resets the flip/ flop 34 and causes the switch 38 to connect the gate 22 to the IVIDA comparator 50 so that any warning generated will be controlled by IVIDA comparator 50. The IVIDA comparator 50 continues to monitor the radio altitude, and no warning is initiated as long as the radio altitude remains above the minimum decision altitude. However, if the altitude drops below the minimum decision altitude and the gate 22 is enabled by the gate 20, the IVIDA comparator will provide a LESS THAN IVIDA signal to the gate 22 to cause the gate 22 to initiate the "TOO LOW" warning by the warning generator 46.

As the aircraft climbs above the minimum decision altitude, but remains below the minimum decision altitude plus a predertermined increment, such as 100 feet (30.5 metres), and as long as the gate 20 provides an enabling signal, the gate 24 will be under the control of a roll-out comparator 52 and a roll angle comparator 54. The function of the comparators 52 and 54 is to monitor the roll angle and barometric descent rate of the aircraft, and to cause the gate 24 to initiate a warning by the warning generator 56 if an unsafe combination of descent rate and roll angle exists.

As previously discussed, aircraft tend to descent as the roll angle is increased. However, this tend- ency is not significant until the roll angle exceeds a predetermined level, such as, for example, 45' for modern fighter/attack aircraft such as the Fairchild A10. Consequently, the roll angle comparator 54 monitors the roll angle signal generated by the gyro platform 18, or similar device indicating the roll angle of the aircraft, and provides an enabling signal to the gate 24 when the roll angle reaches the roll angle at which the aircraft tends to sink. This permits the "ROLL OUT' warning to be gener- ated by the generator 56 if the barometric descent rate exceeds the maximum rate permitted for a given roll angle, as determined by the roll- out comparator 52. The conditions necessary for the "ROLL OU7' warning to be generated are further discussed in connection with the discussion of Figure 3.

Referring to Figure 2, there is shown a graph illustrating the conditions necessary to generate the "TOO LOW" warning and to enable the "FlOLL OUTwarning as a function of airspeed and altitude. These conditions are illustrated by the two shaded areas on the graph. As in apparent from Figure 2, neither warning can be generated as long as the airspeed of the aircraft is below a predeter- mined value, in this embodiment 200 knots. As long as the airspeed of the aircraft exceeds 200 knots (103 metres per second), and the other previously discussed conditions are met, the "TOO LOW' warning will be given whenever the aircraft drops below the minimum decision altitude, or below a predetermined percentage, for example 75%, of the maximum altitude reached on take-off or goaround prior to exceeding the minimum decision altitude.

When the altitude fo the aircraft exceeds the 4 GB 2 175 264 A 4 minimum decision altitude, but is below the mini mum decision altitude plus a predertermined incre ment, such as, for example, 100 feet (30.5 metres), the "ROLL OLIT" warning is enabled. However, the 5---ROLLOUT" warning is not automatically gener- 70 ated when the---ROLLOUT- warning boundary il lustrated in Figure 2 is penetrated, as is the case when the---TOOLOW" warning boundary is pene trated. Rather, the---ROLLOUT- warning mode is only enabled, but the actual warning is produced 75 only if the roll angle exceeds a predetermined an gle, for example 45', and if the descent rate pene trates the boundary of the descent rate curve (Figure 3) which defines the maximum permissible descent rate as a function of roll angle.

A descent rate curve which has been found to be particularly suitable for use in fighterlattack aircraft is illustrated in Figure 3. The shaded area shows the relationship between roll angle and barometric descent rate necessary to generate the---ROLL OUT" warning. As can be seen from Figure 3, the "ROLL OUT- warning is not generated until the roll angle reaches 45', at which point the---ROLLOUT" warning is generated if the barometric altitude de scent rate exceeds 100 feet per minute (0.5 metres 90 per second). As the roll angle is increased to 600, only 50 feet per minute (0.25 metres per second) of descent rate is required to initiate a warning, and when the roil angle reaches 90', no descent at all can be tolerated because the lift provided by the 95 wings under this condition is virtually zero.

Claims (17)

1. A system for providing a warning to the pilot 100 of an aircraft maneuvering near the ground cornprising; means responsive to a signal representative of the roll angle of the aircraft and to a signal representative of the descent rate of the aircraft for gen- 105 erating a warning to the pilot when the combination of roll angle and descent rate exceeds a predetermined level.

2. A system as recited in claim 1 further includ- ing means for preventing te generation of a warning if the altitude of the aircraft exceeds a predetermined level.

3. A system as recited in claim 3 further including means for preventing the generation of said warning if thealtitude of the aircraft drops below a predetermined minimum altitude.

4. A system as recited in claim 3 further including means for generating a different warning if the aircraft drops below said predetermined minimum altitude.

5. A system as recited in claim 4 wherein said system includes means for manually setting said predetermined minimum altitude.

6. A system for alerting the pilot of an aircraft of a dangerous flight condition during low altitude maneuvering comprising; means for generating a first specific warning if the aircraft descends below a minimum altitude, and means for generating a second specific warning above the minimum altitude as a function of the roll angle and descent rate of the aircraft.

7. A system as recited in claim 6 further includ ing means for enabling said second specific warn ing generating means only after the roll angle exceeds a predetermined value.

8. A system as recited in claim 7 wherein said predetermined value of roll angle is approximately 4Y.

9. A system as recited in claim 6 further includ ing means for enabling said second specific warn ing generating means only below a second altitude and above the minimum altitude.

10. A system as recited in claim 9 wherein said second altitude is approximately 100 feet (30.5 metres) above said minimum altitude.

11. A system as recited in claim 6 wherein said descent rate is a barometric descent rate.

12. A system as recited is claim 6 wherein said warning is generated when said roll angle exceeds approximately 45' and the descent rate exceeds approximately 100 feet per minute (0.5 metres per second).

13. A system as recited in claim 6 wherein said warning is generated when said roll angle exceeds approximately 60' and the descent rate exceeds apprroximately 50 feet per minute (0.25 metres per second).

14. A system as recited in claim 6 wherein said warning is generated when said roll angle exceeds approximately 90' and the descent rate exceeds approximately 0 feet per minute (0 feet per seeond).

15. A system as recited in claim 6 wherein said predetermined value of descent rate is an inverse function of the roll angle.

16. A system as recited in claim 15 further including means for enabling said first and second specific warnings means only when the airspeed exceeds a predetermined value.

17. A system as recited in claim 16 wherein said predetermined value of airspeed is approximately 200 knots (103 metres per second).

Printed in the UK for HMSO, D8818935, 10186, 7102. Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.