CA1241083A - System for alerting a pilot of a dangerous flight profile during low level maneuvering - Google Patents

Abstract

*

SYSTEM FOR ALERTING A PILOT OF A
DANGEROUS FLIGHT PROFILE DURING LOW LEVEL MANEUVERING
Abstract of the Disclosure 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, and provides a first specific warning to the pilot if the altitude of the aircraft drops below a predetermined minimum altitude above ground. The system further monitors the roll angle and descent rate of the aircraft to provide a second specific warning if the descent rate of the aircraft exceeds a predetermined rate determined by the roll angle of the aircraft if the aircraft is below a second pre-determined altitude above ground.

Description

~2410~

1 This application is a division of application serial number 449,619, filed March 14, 1984.
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 should descend below a predetermined minimum altitude above ground, or if the aircraft exceeds a predetermined descent rate while performing turning maneuvers or other maneuvers requiring a roll. Distinct ,pecific warnings are given in order to inform the pilot of ~he specific action that must be taken to recover from a ~angerous flight profile.
Description of the Prior Art Ground proximity warning systems 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 aircraft to attain an excessive descent rate after take-off or on approach. An ~sxample of a system that provides a pilot with a warning if he drops below a predetermined minimum desired altitude 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 '; ,~ `.

o~

-2-operation if the aircraft should descend at an excessive barometric rate or lose a predetermined amount of barometric altitude are disclosed in United States patent Nos. 3,946,358; 3,947,808, 3,947~810 and 4,319,218;
assigned to the same assignee as the present invention.
While these systems serve to provide the pilot with a warniing in the event that the aircraf~
drops below a preset minimum desired altitude above ground, or if the aircraft descends excessively after take-off or a missed approach, such svstems are designed primarily for transport aircraft that do ~ot normally fly at low altitudes or execute turns or other severe or violent maneuvers near the groundD Conseouently, such systens would not normally provide adequate warn-ing to the pilot of a highl~ maneuvera~le aircraftsuch as, fc)r example, a fighter/attack aircraft execut-ing tactical maneuvers near the ground.
SUMMA~Y OF TEE INVENTION
l~ccordingly, it is an object of the present invention 1:o provide a warning system that overcomes many of the disadvantages of the prio~ art warning systems during high speed, low level naneuvering phases of aircraft operation.
[t is another o~ject of the present invention to provide a warning system ~esigned to provide the piaOt of a high performance aircraft such as a fighter/attack aircraft cruising at low altitude with a warning indicating a dangerous flight condition in sufficient time to perm~t him to take corrective action.
~ t is another object of the prese~t in~en-tion 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 excessive descent rate in sufficient time to permit the pilot to take corrective action.
It is yet another object of the present invention to 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 dis-tracted or disoriented, there is a danger of inadver-tent descent into terrain or flight into slowly rising terrain. The danger of flying into rising terrain exists primarily during take-off, and during low alti-tude 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 suk-jected to high roll angles.
Therefore, in accordance with a preferred embodiment of the invention, there is pxo~ided a warn-ing system that senses the altitude of the aircraft above the ground utilizing a radio altimeter or the like, and provides a specific aural warning, such as "TOO LOW" to the pilot if the aircraft descends below a predetermined minimum desired altitude above ground, thereby providing protection during low altitude cruise phases of operation. The predetermined minimum desired altitude is typically the minimum decision altitude which is manually set by the minimum decision altitude marker or altimeter "bug" present on a radi~
altimeter indicator.
Also, in order to provide a warning during take-off into rising terrain, or during an inadvertent descent before the minimum decision altitude is reached, lOR3 the system is provided with an accumulator that monitors the radio altitude after take off and stores the highest altitude reached after take-off. In the event that the aircraft descends below a predetermined percentage of the maximum radio altitude reached prior to reaching the minimum decision altitude, a warning is also generated. Typically, this warning will be the same "TOO LOW" warning that is generated if the minimum decision altitude is ~enetrated in order to indicate to the pilot that he is too low.
In additionf the system monitors the roll angle of the aircraft and generates a second specific warning in the event that the aircraft is below a second predetermined altitude r and exceeds a predeter~
mined 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 pil~t to diagnose the problem quickly, and in the present embodiment, a warning such as the warning ~ROLL OUT"
- or similar term is provided.
DESCRIPTION OF THE DRAWING
These and other objects and advantagec; of the present invention will become apparent upon con-sideration of the following detailed description and attached drawing, wherein:
FIG. 1 is a logical block diagram of the warning system according to the invention;
FI~c 2 is a graph illustratin~ the relation-ship between airspeed and radio altitude where warnings may be generated; and FIG. 3 is a graph showing the relationship between barometric altitude rate and roll angle required ~ ~'.4~083 to generate a warning that the aircraft is descending at an excessive rate during a roll maneuver.
DETAI LED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawing, with particular attention to FIG. 1, there is illustrated an embodiment of a ground proximity warning system according to the invention particularly useful for providing warnings of unsafe flight conditions during low level maneuver-ing generally designated by the reference numeral 10.
The system 10 according to the invention is illustrated in FIG. 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 ~5 logic can be other than as shown irl FIG. 1, with various digital and analo~ implementations being possible~
The signals used by the warning system as described include radio altitude, barometric altitude rate, airspeed, engine RPM, roll angle of the aircraft, the 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, th~ signals shown in FIG~ 1 can be obtained from individual instru-ments such as a barometric altimeter 12, a barometricaltitude rate circuit 14, a radio altimeter 16 and a gyroscopic platform 18, as well as various discrete circuit elements such as a discrete elem~nt indicating the position of the landing gear. These signals may also be obtained from a digital data bus in certain newer aircraftO
As previously stated, the system according to the invention is designed to pr~vide different warnings during different phases of aircraft operation.
For example, the system is designed to provide a irst 6~ 08~

warning, such as, for example, an aural or voice warn-ing ~TOO LOW" should the aircraft descend below the minimum decision altitude during low level cruise.-This warning will also be generated if the aircraft should lose a predetermined percentage of the altitude attained after take-off, but prior to reaching the minimum decision altitude. In addition, the system is designed to provide a second specific warning, such as, for example, the aural or Yoice signal "ROLL OUT~
should the aircraft descend too rapidly during a roll maneuver~ Consequently, 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 or low level maneuvering so that the appropriate warning will be generated should cer~ain flight parameters be exceeded. This function is pro-vided by the logic circuitry including AND gates 20, 22, 24, 26, and 28, an OR gate 30, a pair of set/reset flip-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 flight, certain determinations must be made to determine whether the aircraft ii indeed in one of the aforemen-tioned phases. The initial determinations are made by the AND gate 20 which provides an enabling signal to the AND gates ~2 and 24 only if 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 landing configuration. Also, for the system to be operational, the barometric alti-meter 12t the barometric rate circuit 14 and the radio o~ ' altimeter must be operating properly. Consequently,signals indicating 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 detel-mining whether the air~
craft is flying in a configuration other than a land-ing configuration and that the instruments are operat-ing properly, it is necessary to determine whether the aixcraft 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 ~6 and 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 condi-tions that take-off power is present and that the ~anding gear is up are met. If both corlditions are met, the set/reset flip-flop 32 is reset. Signals indicative ~f take-off power ~hat 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, or from a discrete element indicating thxottle posi-tion. An engine tachometer, which indicates for example~ the RPM of the ~rimary 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 ~.4~~ ~

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 or the aircraft is below 100 feet and the engine is not producing take-off power and the speed of the aircraft is below 200 knots. 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 flip-flop 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 transition 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 FIG. ~, thereby to connect one input of the gate 2~ to circuitry including a too low comparator 40, a scaling circuit 42 and a radio altitude accumulator 44. These devices determine when a "~OO 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 minimum decision altitude (MDA), an MDA comparator 50 provides a signal indicating that the aircraft has exceeded the minimum decision altitude in order to reset the input of the flip-flop 34, thereby resetting 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 connected to a LESS THAN MDA output of the ~DA comparator 50, thereby making the system responsive to any descents below the minimum decision altitude. Consequently, if the aircraft drops below the minimum decision altitude _9~ 0~3 when in this mode, the warning generator 46 will gener-ate the ~TOO LOW" warning and apply it to the trans-~ucer 48.
As long as the altitude of the aircraft is below the minimum decision altitude plus a predeter-mined increment, such as, for example, 100 feet, but not below the minimum decision altitude, the AND gate 24 is enabled by the comparator 50 via the GREATER
T~AN MDA and LESS ~HAN MDA I 100 FEET signals applied to two of its inputs. When so enabled, the AND gate 24 is made responsive to a pair of comparators 52 and 54 to operate a second warning generator 56 which generates a second warning such as, for example, ~ROLL
OUT" when the descent rate of the aircraft exceeds a predetermined level for a given rolt angle.
Discussing the operation in greater ~3etailt as the aircraft takes off, the flip-flop 32 is reset, thereby causing the transition detector 36 to ~?rovide an output pulse to set the flip-flop 34 to thereby connect the gate 22 to the comparator 40. The output pulse from the transition detector 36 also re~ets the radio altitude accumulator to zero, or to a predeter-mined low value setting~ such as, for example, 50 feet. 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 radio 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 comparator 40 which controls the opera-tion 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 altitude remains above the maximum radio altitude -10~ 083 multiplied by the scaling factor, no warning is gener-ated. 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 generator 46 and cause the generator 46 to generate the ~TOQ LOWn warning and apply it, either directly or indirectly, to the trans-ducer 48, provided that the other input of the gate22 is enabled by the gate 20. The radio altitude signal from the altimeter 16 is also applied to the MDA comparator 50 which monitors the radio altitude signal ffom the radio altimeter 16 and provides a GREATER THAN MDA signal to the flip-flop 34 when the radio altitude exceeds the minimum decision altitude. ~his signal resets the flip-flop 34 and causes the switch 38 to connect the gate 22 to the MDA comparator 50 so that any warning generated will be controlled by MDA comparator 50. ~he MDA
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 MDA com-parator will provide a LESS THAN MDA 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 predetermined increment, such as, 100 feet 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 08`3 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 descend as the roll angle is increased. However, this tendency is not significant until the roll angle exceeds a predetermined level; such as, for example, }o 45 for modern fighter/attack aircraft such as the Fairchild A10. Consequently, the roll angle compara-tor 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 generated 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 com-parator S2. The conditions necessary for the "ROLL
OUT" warning to be generated are further discussed in connection with the discussion of FIG. 3.
Referring to FIG. 2, there is shown a graph illustrating the conditions necessary to generate the "TOO LOWn warning and to enable the "ROLL OUT" warning as a function of airspeed and altitude. These condi-tions are illustrated by the two shaded areas on the graph. As is apparent from FIG. 2, neither warning can be generated as long as the airspeed of the air-craft is below a predetermined value, in this embodi-ment 200 knots. As long as the airspeed of the air-craft exceeds 200 knots, and the other previously discussed conditions are met, the 'iTOO LOW" warning will be given whenever the aircraft drops below the ~ 0~3 minimum decision altitude, or below a predetermined percentage, for example 75%, of the maximum altitude reached on take-off or go-around prior to exceeding the minimum decision altitude.
When the altitude of the aircraft exceeds the minimum decision altitude, but is below the mini-mum decision altitude plus a predetermined increment, such as, for example, 100 feet, the ~ROLL OUT" warning is enabled. However, the "ROLL OUT" warning is not automatically generated when the "ROLL OUT" warning boundary illustrated in FIG. 2 is penetrated, as is the case when the "TOO LOW" warning boundary is pene-trated. Rather, the ~ROLL OUT" warning mode is only enabled, but the actual warning is produced only if the roll angle exceeds a predetermined angle, for example, 45, and if the descent rate penetrates the boundary of the descent rate curve (~IG. 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 fighter/attack aircraft is illustrated in FIG. 3. The shaded area shows the relationship between roll angle and baro-metric descent rate necessary to generate the ~ROLk OUT" warning. As can be seen from FIG. 3, the "ROLL
OUT" warning is not generated until the roll angle reaches 45, at which point the "ROLL OUT" warning is generated if the barometric altitude descent rate exceeds 100 feet per minute. As the roll angle is increased to 60, only 50 feet per minute of descent rate is required to initiate a warning, and when the roll angle reaches 90, no descent at all can be tolerated because the lif t provided by the wings under this condition is virtually zero.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings.- Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically des-cribed above.

Claims (19)

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

1. 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.

2. A system as recited in claim 1 further including means for enabling said second specific warning generating means only after the roll angle exceeds a predetermined value.

3. A system as recited in claim 2 wherein said predetermined value of roll angle is approximately 45°.

4. A system as recited in claim 1 further including means for enabling said second specific warning generating means only below a second altitude and above the minimum altitude.

5. A system as recited in claim 4 wherein said second altitude is approximately 100 feet above said minimum altitude.

6. A system as recited in claim 1 wherein said descent rate is a barometric descent rate.

7. A system as recited in claim 1 wherein said warning is generated when said roll angle exceeds approximately 45 and the descent rate exceeds approximately 100 feet per minute.

8. A system as recited in claim 1 wherein said warning is generated when said roll angle exceeds approximately 60°
and the descent rate exceeds approximately 50 feet per minute.

9. A system as recited in claim 1 wherein said warning is generated when said roll angle exceeds approximately 90°
and the descent rate exceeds approximately 0 feet per minute.

10. A system as recited in claim 1 wherein said predetermined value of descent rate is an inverse function of the roll angle.

11. A system as recited in claim 10 further including means for enabling said first and second specific warning means only when the airspeed exceeds a predetermined value.

12. A system as recited in claim 11 wherein said predetermined value of airspeed is approximately 200 knots.

13. A system for providing a warning to the pilot of an aircraft maneuvering near the ground comprising:

Claim 13 continued...

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 generating a warning to the pilot when the combination of roll angle and descent rate exceeds a predetermined level.

14. A system as recited in claim 13 further including means for preventing the generation of a warning if the altitude of the aircraft exceeds a predetermined level.

15. A system as recited in claim 14 further including means for preventing the generation of said warning if the altitude of the aircraft drops below a predetermined minimum altitude.

16. A system as recited in claim 15 further including means for generating a different warning if the aircraft drops below said predetermined minimum altitude.

17. A system as recited in claim 16 wherein said system includes means for manually setting said predetermined minimum altitude.

18. A system as recited in claim 17 further including means for automatically setting said predetermined minimum altitude to a predetermined percentage of the maximum altitude reached after take-off if the aircraft has not yet reached the manually set minimum altitude.

19. A system as recited in claim 18 wherein said predetermined percentage is approximately 75%.