Integrated ground collision avoidance system

Abstract: A ground collision avoidance system that is accurate and avoids nuisance warnings and displays provides an invaluable system for the preservation of life and equipment. This system improves its accuracy and performance by integrating with all other aircraft systems including guidance systems, navigation systems, digital terrain elevation databases, mission computers, and radar altimeters. Furthermore, the ground collision avoidance system provides a multiple processing path to determine numerous predicted flight paths based on a number of reasonable assumptions regarding the aircraft flight during a predetermined amount of time. By using prediction scheme a realistic estimate of the predicted flight path envelope can be determined and then this information can be used in conjunction with accurate terrain elevation databases to determine whether a ground collision condition exists. On the basis of these calculations appropriate warnings can be provided to the air crew as well as suggested maneuvers to avoid ground collision.

Description: BACKGROUND OF THE INVENTION The present invention relates generally to ground collision avoidance system. More specifically, the present invention relates to an integrated ground collision avoidance system utilizing numerous sensors and cross checks to provide an accurate ground collision warning while at the same time avoiding unnecessary nuisance warnings. As is well known in the aviation fields, avoiding controlled flight into the ground or ground collision is a very important endeavor. Every year many lives are lost due to the collision between an aircraft and the ground. Many times ground collision is caused by the pilot having misinformation or becoming disorientated and flying directly into the ground. Furthermore, ground collision is a problem for both military and commercial aircraft alike. Therefore, to promote the safety of air travel, systems that avoid collision with the ground are highly desirable. In the past numerous systems have been developed to provide such ground collision avoidance. One type of system utilizes aircraft sensors to determine the proximity of the aircraft to the ground. These sensors can include barometric altimeters, radar altimeters, and forward looking infrared radar. While such equipment does provide a warning of the possibility of collision with the ground, these systems are highly limited by the capabilities of the sensors themselves. A second type of system utilizes a predetermined minimum safe altitude for given region in which the aircraft is traveling. Consequently, if the aircraft travels below this predetermined minimum safe altitude, a warning indicates to the pilots that they are in danger of ground collision This system is fine for providing general warnings in a flat terrain environment. However, in certain situations, such as fighter aircraft performing terrain following missions, when an aircraft is required to travel at low altitudes above the ground this system is impractical. This is especially true in geographic regions having large variations in elevation. Another system for providing ground collision avoidance warnings is one wherein the flight dynamics of an aircraft are constantly monitored to provide an indication of possible collision. More specifically, the altitude loss is monitored during numerous maneuvers and is subsequently interpolated to determine whether ground collision is eminent. This type of system, however, is incapable of predicting the true ground situation and the maneuvering controls or considering maneuvering alternatives available to the pilot. It is well known that while in a dive typically a pilot will eventually pull out. If altitude loss interpolation is carried out at this point a false warning or nuisance warning will surely sound. For this reason this type of system is also impractical. EP 0 565 399 A1 corresponding to U.S. 5 488 563 discloses an anti-collision system which uses a digital terrain database. This device includes a mass memory which is capable of storing a database representing at least a substantial part of the terrestrial globe, in a cutout form comprising a grid configuration on at least one level. These types of grids can include a basic grid, intermediate grids, subdividing basic grids, and ultimate grids subdividing in turn some of the intermediate grids. The intermediate and ultimate grids are provided in areas in a vicinity of an airport. The more precise database allows the aircraft to maneuver more safely in areas where a collision is of a greater possibility. EP 0 597 760 A1 corresponding to U.S. 5 414 631 discloses a device for avoiding aircraft collisions with the ground which determines the geographical location of the aircraft and includes a database containing a description of safety altitudes for the geographical location. The device measures whether the aircraft is at a safe altitude relative to the terrain in the database and if it is not, an alarm is sounded. One overriding consideration when designing a ground collision avoidance system is the avoidance of constant false warnings or nuisance warnings. Systems can be devised having differing sensitivities and differing warning methodology. However, these systems are of no use to a pilot if they provide continuous nuisance warnings suggesting that the pilot is in eminent danger of ground collision, when in reality the pilot is flying in a safe condition. If to many nuisance warnings are provided, the ground collision avoidance system will likely be disabled and at that point become totally useless. For this reason it is desirable to provide a very realistic system capable of providing ground collision avoidance warnings only at a point when they are likely to be meaningful and heeded by the flight crew. SUMMARY OF THE INVENTION The present invention provides an integrated system that utilizes all available on board sensors and systems to generate accurate ground collision avoidance warnings. Some of the presently available on board aircraft systems include inertial reference or inertial navigation systems, global positioning systems (GPS), radar altimeters, air data sensors, mission computers, flight control computers, multi function displays, digital map systems, active terrain sensors, terrain reference navigation systems, and heads up displays (HUD). By utilizing the information provided by all of these systems an accurate ground collision avoidance warning can be produced without adding considerable amounts of hardware to an aircraft. The system of the present invention provides a ground collision avoidance system which is scaleable or modifiable based on the specific configuration of the aircraft platform being utilized or the mission being flown. This scaling capability allows the system to be tailored to the present aircraft capabilities. Consequently, this system is much more accurate. Examples of such tailoring include setting response times according to high performance fighter aircraft as opposed to air transport type aircraft. In producing an accurate ground collision avoidance warning the present system correlates and blends all available information regarding localized terrain to create a very accurate image of the terrain situation over which the aircraft is operating. Also the present system makes some basic assumptions to predict the most possible or probable flight paths that will be flown and maneuvered by the aircraft. These two sets of data can then be correlated, and the flight path can be mapped to the ground. These predicted flight paths can then be used in conjunction with projected ground path way to determine whether ground collision condition is eminent and thus if a warning is warranted. These possible flight envelopes are predicted and then utilized by the system to determine ground collision conditions. Such flight envelope mapping or ground mapping after corrected for terrain variances allows for very reliable and accurate assessments of collision conditions. Once a ground collision condition has been determined the present system provides further guidance and control to avoid this possible ground collision situation. This avoidance control can provide for both pitch and roll commands while also providing thrust commands to guide the aircraft to a target with a clearance altitude so as to avoid collision. In conjunction with all the previous capabilities the system of the present invention provides both visual and concise audio warnings to the air crew. Visual warnings can be provided via the multifunction displays, a dedicated ground collision display or heads up displays. Audible warnings can be provided via speakers and/or buzzers within the cockpit. The display warnings can be configured to provide a number of different levels of warning conditions to the air crew including warning of collision possibilities to eminent collision conditions. It is an object of the present invention to provide meaningful, useful, and accurate ground collision warnings to any air crew operating an aircraft. These warnings are of no use if the ground collision avoidance system provides numerous unwarranted warnings thus causing them to be classified as false alarms or nuisance warnings. It is also an object of the present invention to provide a ground collision warning system that integrates all capabilities existing within an aircraft. This is accomplished by utilizing the outputs provided by other systems such as mission computer, navigation systems, flight control computer systems, digital map systems, etc. It is a further object to the present invention to provide a ground collision warning system that can be tailored for each particular aircraft application and each mission flown. More specifically, it is an object of the invention to provide a system that can be altered to match the performance characteristics of the aircraft within which the system is operating. Such tailoring or scaleability causes the ground collision warning system to be much more accurate because the system can accurately predict the maneuvering capabilities of the aircraft. BRIEF DESCRIPTION OF THE DRAWINGS Further objects and advantages of the present invention can be seen by reading the following detailed description in conjunction with the drawings in which: Fig. 1 is a block diagram of the integrated ground collision avoidance system controller and its relationship to numerous other aircraft systems; Fig. 2 is a logic flow diagram outlining the process followed by the integrated ground collision avoidance system controller; Fig. 3 is a block diagram illustrating the portions of the localized terrain awareness system; Fig. 4 is a logic flow diagram outlining the process followed by the localized terrain awareness system; Fig. 5 is a block diagram illustrating the flight envelope prediction system; Fig. 6 is logic flow diagram illustrating the logic followed by the flight envelope prediction system; Fig. 7 is block diagram outline the ground correlation and collision condition system; Fig. 8 is a flow diagram outline the logic followed by the ground correlation and collision condition system; Fig. 9 is a block diagram outlining the avoidance control and guidance system of the present invention; and Fig. 10 is a logic flow diagram outlining the logic followed by the avoidance control and guidance system. DETAILED DESCRIPTION OF THE INVENTION Referring now to Fig. 1, there shown is a block diagram of the integrated ground collision avoidance system 10 along with a number of other typical aircraft systems. Generally, an aircraft contains a number of avionics systems connected to some kind of avionics bus 20. In conjunction with the integrated ground collision avoidance system 10 (IGCAS 10), Fig. 1 shows a heads up display 22, a mission computer 24, a radar altimeter system 26, and inertial navigation system 28, a global positioning system 30 (GPS), a data memory unit 32, a multi function display 34, a flight control computer 35, a map and mission module 36, air data sensors 37, active terrain sensors 38, and a terrain referenced navigation system 42. While these systems are exemplary of those attached to a typical avionics bus 20 it will be understood that numerous other systems may be and typically are connected. Avionics bus 20 allows all these systems to share information and communicate with one another. One typical example of the avionics bus is the MIL STD-1553 bus used in most military application, an ARINC bus used in commercial application. Integrated ground collision avoidance system 10 contains a number of components each of which provides a specific capability. While each of these components has dedicated purposes it will be recognized that they continue to communicate with one another and share information at all times. Included within integrated ground collision avoidance systems 10 is a localized terrain awareness system 40, a flight envelope prediction system 50, a ground correlation system 60, an avoidance control and guidance system 70, and a collision warning generator 80. Localized terrain awareness system 40 coordinates the numerous sensors and systems on the aircraft that deal with terrain elevation sensing. Localized terrain awareness system 40 then correlates and overlays these data to build a complete image of the terrain and feature situation over which the aircraft is operating. Flight envelope prediction system 50 coordinates with the flight control computers 35, mission computer 24 and the inertial navigation systems 28 to provide one or more predicted flight envelopes within which the aircraft will be traveling during a predetermined period. Flight envelope prediction system 50 calculates a number of reasonable flight envelopes based on the extended current flight trajectory and the possible maneuvers that a pilot is likely to carry out. Flight envelope prediction system 50 also operates with the high fidelity aircraft model to accurately predict the possible maneuvering capabilities of the aircraft. In this way the flight envelope prediction system 50 can be modified for different types of aircraft thus allowing a more accurate prediction of aircraft maneuverability. Ground correlation system 60 utilizes the information provided by localized terrain awareness system 40 and flight envelope prediction system 50 to ground map the aircraft's flight. This ground mapping is accomplished by projecting the possible flight paths upon the correlated terrain and feature image over which the aircraft is flying. From this ground correlation a warning situation can be detected wherein it is determined that ground collision is imminent or if no further corrective action is taken. Avoidance control and guidance system 70 utilizes the information from the previously mentioned systems and determines the appropriate maneuvering action to avoid eminent collision. Avoidance control and guidance system 70 then can provide the pilot or air crew with appropriate "fly out" commands to avoid ground collision. Lastly, ground collision warning generator 80 provides the necessary warnings and displays to the pilot and air crew to alert them to possible ground collision and provide them with the visualized vertical terrain profile and, predicted flight path, and highlighted collision point. Ground collision warning generator 80 has attached thereto audio warning system 82 and a ground collision warning display 84. Audio warning system 82 provides audible warnings to the pilot such as buzzers or possible "fly out" cueing commands. Similarly, ground collision warning display 84 can display the possible collision situations to the pilot as well as display the necessary evasive maneuvers to assist the pilot in avoiding ground collision. Referring now to Fig. 2, there shown is a more detailed diagram of the flow logic followed by integrated ground collision avoidance controller 90. The IGCAS controller 90 starts the process by initializing and setting up system capabilities in the collision system in block 130. The system then moves on to localize terrain awareness in block 132. This process involves a complete evaluation of the terrain over which the aircraft is operating. Further elaboration ofthe localized terrain awareness 132 is found later in the present specification in relation to the discussion of Figs. 3 & 4. The system them moves on to the prediction of probable flight envelopes in block 134. Flight envelope prediction block 134 calculates the possible flight trajectories based upon the current dynamic state of the aircraft, dynamics constraints, and the probable aircraft recovery maneuvers. Again, further elaboration on the process followed by the flight prediction envelope block 134 is contained in the specification in relation to the discussion of figs. 5 & 6. The process is then moves on to the ground correlation block 136 wherein the predicted flight envelopes are correlated with ground data. This involves retrieving elevation and feature data corresponding to the aforementioned flight envelopes. From this retrieved data and the resulting correlation, the system can determine if high probability of a collision condition exists. This process is further discussed in relation to Figs. 7 & 8. The process then moves on to calculate avoidance control and guidance commands in block 138 wherein collaboration with 134 and 136 to determine ground and terrain avoidance flight path and based on this commands are generated which can then be sent to the aircraft's flight control system to avoid a collision. Further, the commands can be provided to the multi-function display to generate flight director commands and to head up display to generate avoidance pathway in sky. These avoidance commands are based upon the predicted ground and avoidance flight path and the dynamic and performance capabilities of the aircraft. Further discussion of this process is contained in the present specification in relation to Figs. 9 & 10. Lastly, the present system generates appropriate warnings in collision warning generation block 140. These warnings indicate to the pilot that ground collision is imminent unless indicated evasive action is taken. Concurrently, appropriate guidance commands are provided to the pilot. (i.e. the avoidance control and guidance commands generated in block 138) Referring now to Fig. 3, there shown is a block diagram illustrating the localized terrain awareness system 40. As previously discussed, localized terrain awareness system 40 relies on inputs from a number of different devices. These devices include the digital terrain elevation database 32, active terrain sensors 38, radar altimeter 26, mission computer 24, terrain reference navigation system 42, and worldwide navaid and airport indicator 43. These are the systems available to the localized terrain awareness system 40. All the numerous inputs are utilized by localized terrain awareness system 40 to build and fuse a complete verticle profile of the geographical area over which the aircraft in operating. This picture includes an accurate picture of the terrain elevation and the geographic formations over which the aircraft is presently flying or will be flying in the near future. Localized terrain awareness system 40 contains a localized terrain elevation system 44 that receives inputs from digital terrain elevation database 32, terrain referenced navigation system 42, and mission computer 24. From these numerous inputs, the localized terrain elevation system 44 can determine where the aircraft is flying and the corresponding terrain for the area over which the aircraft is presently flying. Furthermore, localized terrain elevation system 44 can anticipate the next region over which the aircraft will be flying and provide elevation data for that region as well. Much of the elevation information is received from digital terrain elevation database 32. Digital terrain elevation database 32 contains elevation data for large geographical areas and manipulates this data to provide elevation data in manageable portions. A localized airport and runway system 45 receives inputs from a worldwide navaid and airport data system 43, the terrain referenced navigation system 42, the flight control computer 35 and the mission computer 24. From these inputs the localized airport and runway mapping system 45 can determine exactly when the aircraft is in the vicinity of an airport and when the aircraft has begun to initiate its approach for a landing. Typically the worldwide navaid and airport data system 42 may include an ILS system, VOR system, or a glide slope verification system. This information is particularly relevant because numerous nuisance warnings can be avoided if the IGCAS 10 is aware that the aircraft is approaching the ground because it needs to land. Localized terrain awareness system 40 also contains an active terrain monitoring system 46 that receives inputs from radar altimeter 26 and active terrain sensors 38. Active sensors 38 may include laser range finders, infrared radar, or other well known proximity sensors. Active terrain monitoring system 46 receives these inputs and calculates a plurality of elevation information for the geographic region over which the aircraft is operating. Output from localized terrain elevation system 44, the localized airport and runway system 45, and active terrain monitoring system 46 is provided to a local terrain correlation system 48. Also providing an input for terrain accuracy to local terrain correlation system 48 is terrain reference navigation system 42. Local terrain correlation system 48 then correlates all the altitude and terrain information received and provides an output that, in summary, provides a complete picture of terrain over which the aircraft is presently operating and the terrain over which the aircraft may soon be operating. This correlation is accomplished by comparing and then combining outputs from the active terrain monitoring system 46, localized airport and runway system 45, and localized terrain elevation system 44. Outputs from the terrain reference navigation system 42 are then used to enhance the fidelity of the local terrain correlation system 48 and provide a comprehensive view of the local terrain. This localized terrain data is then output on bus connection 49. While numerous inputs to localized terrain awareness system 40 are shown, it is understood that these inputs could be accomplished through numerous bus connections and other types of electronic communication. Furthermore, the outputs from localized terrain awareness system 40 are then available on the IGCAS bus 14. Referring now to Fig. 4, there shown is a flow diagram illustrating the logic steps followed by localized terrain awareness system 40. Initially, the terrain elevation data and the flight dynamics data are monitored to localize the terrain elevations in block 150. Localization of the terrain elevation data simply involves the retrieval of elevation data corresponding to the area over which the aircraft is flying. Following the localization of terrain elevation data 150, airport and runway data is localized, and fusing where appropriate, in block 152. Similarly, this localization involves the retrieval of airport and runway data corresponding to the area over which the aircraft is operating. Localization of data relative to runways and airports will be relevant only during certain periods of aircraft operation, however, an indication of take-off or landing maneuvers is very essential if nuisance warnings are to be avoided. The process then performs active terrain filtering and monitoring in block 154. This activity provides a cross-check for fusing of the aforementioned terrain elevation localization (performed in block 150) and the runway and airport localization (performed in block 152). Lastly, all of the localized terrain information obtained (localized terrain elevation data, localized airport and runway data, and active terrain monitoring data) is correlated in block 156 so as to provide a complete vertical profile of the local terrain over which the aircraft is operating. Referring now to Fig. 5, there shown is a more complete block diagram of flight envelope prediction system 50. The system contains a flight phase monitor 56, an outer-loop guidance control generator 58, a first predicted flight path system 52, a second predicted flight path system 54, and an aircraft dynamics model 39. While the present embodiment shows two predicted flight path systems it will be understood that more of these types of systems could be incorporated as necessary. Flight phase monitor 56 keeps track of exactly which phase of the flight the aircraft is in (e.g. takeoff, landing, level flight, high maneuverability, ...). The particular phase of a flight will seriously effect the assumptions a first predicted flight path system 52 and a second predicted flight path system 54 will make when carrying out their processes. After the flight phase has been identified, this information is transited to outer-loop guidance control generator 58. Outer-loop guidance control generator 58 generally produces the commands provided to the aircraft which cause the aircraft to follow its navigation plan. Inputs are received from inertial navigation system 28 and air data sensors 37, in addition to the input from flight phase monitor 56. Outer-loop guidance control generator 58 then provides outputs indicative of the planned aircraft flight path. The outputs from outer-loop guidance control generator 58 are then provided to first predicted flight path system 52 and second predicted flight path system 54. From these inputs first predicted flight path system 52 can determine the position of the aircraft at the time and predict a flight envelope through which the aircraft is likely to fly in a predetermined period. First predicted flight path envelope, generated by first predicted flight path system 52, is based on the general assumptions that the aircraft will follow its current heading and attitude during the predetermined interval. Second predicted flight path system 54 operates similarly to produce a second predicted flight envelope through which the aircraft is likely to maneuver. However, second predicted flight path system 54 differs from first predicted flight path system 52 in that it makes different assumptions based on likely aircraft commands. Second predicted flight path system 54 assumes that a reasonable maneuver will be made during the predetermined duration. This system looks at the present altitude, altitude rates, heading, flight control mode state and the mode state of a mission computer 24, to aid in determining if it is likely that the aircraft will perform a maneuver during the predetermined interval. Assuming this maneuver is to be made the second predicted flight envelope will be created based on that maneuver. The outputs from first predicted flight path system 52 and second predicted flight path system 54 are then provided to aircraft model 39 to assure the predictions are accurate. Aircraft model 39 contains information regarding the maneuverability ofthe aircraft and assures that certain flight paths can actually be followed. The predicted flight paths (first and second) are then output to the IGCAS bus 14 for use by other systems. Referring now to Fig. 6, there shown is a logic flow diagram, which is typically used by the flight envelope prediction system 50. The process used for flight envelope prediction begins at block 160 where the flight phase monitor is checked to determine exactly which phase of flight the aircraft is in. The process then moves on to block 162 where the current outer-loop guidance commands are examined to determine the progress of the aircraft is made with respect to time or maneuvering phase. Also, the upcoming aircraft control segments can be checked to gain some insight regarding the aircraft's position relative to the flight plan. The outer-loop guidance commands for the predicted flight paths are also determined based on this information. Information related to the aircraft's present maneuver is then processed to predict a first flight path in block 164. In parallel with the prediction of the first predicted flight path a second flight path is predicted in block 168. Each of the steps of predicting the first and second flight path are based upon the current flight operation of the aircraft along with a number of predetermined assumptions. For example, prediction of the first flight path may be based upon the assumption that the current maneuver/aircraft attitude will be maintained. Alternatively, the second flight path may be predicted based on the assumption that the aircraft is going to return to level flight as soon as possible and start a climb out maneuver. These are two example criterion that may be used in predicting the aircraft flight paths, however it will be understood that many other assumptions may be applicable. Next, in blocks 166 and 170 the reduced order and high fidelity aircraft model is applied to the predicted flight path to insure the predicted flight paths are realistic. The aircraft model, as previously discussed, contains information regarding the performance limitations of maneuverability of the host aircraft. This check of the aircraft model can possibly allow for corrections in the first and second predicted flight paths based upon the aircraft maneuverability. Following the application of the aircraft model the first flight path data 172 and second flight path data 174 are provided to the IGCAS bus 14 for use by other components of the system. Now referring to Fig. 7, there shown is a block diagram illustrating the ground correlation system 60. Attached to ground correlation system 60 is localized terrain awareness system 40, predicted flight envelope system 50, inertial navigation system 28, and mission computer 24. Contained within the ground correlation system 60 is a ground pathway mapping system 100, a ground collision correlation system 108, a maneuver replanning system 104, normalized ground pathway system 106, and aircraft model 39. Ground pathway mapping system 100 receives inputs from the localized terrain awareness system 40, maneuver replanning system 104, and predicted flight envelope system 50. From these inputs ground pathway mapping system 100 can project the aircraft pathway onto the terrain over which the aircraft is operating. This ground pathway mapping is then transmitted to normalized ground pathway system 106 for normalizing the ground pathway. The normalized ground pathway is a collection of information relating to the terrain and terrain accuracy over which the aircraft is to fly. The normalized ground pathway provides the highest data point for a certain segment of the pathway. Also some error term may be added to the ground data to provide a most probable elevation corresponding to the pathway. The normalized ground pathway is then provided to ground collision correlation system 108. Ground collision correlation system 108 receives an input from flight envelope prediction system 50 along with an input from the aforementioned normalized ground pathway system 106. From these systems, ground collision correlation system 108 determines if, based on the information provided, a ground collision is possible within a predetermined time interval. If such a collision is possible appropriate signals and warnings are provided. This collision condition determination is based upon numerous aforementioned assumptions including: (a) the alternative flight paths determined by flight envelope prediction system 50, and (b) the maneuvering capabilities of the aircraft as provided by aircraft model 39. From all this information the probability of a collision condition can also be determined. The probability of collision can be rated on a scale of "possible provided certain flight dynamics are followed" to "imminent collision if no evasive action is taken." This information can then be provided to further systems to produce the appropriate warnings to the air crew. The results of the ground collision correlation system 108 are then provided to maneuver replanning system 104 and to IGCAS bus 14 via output 110. As previously mentioned, ground correlation system 60 also includes maneuver replanning system 104 which receives signals from mission computer 24, aircraft model 39, and ground collision correlation system 108. Maneuver replanning system 104 then utilizes these inputs to appropriately replan the intermediate flight segments based on the flight information provided by mission computer 24 and collision condition indications as provided by ground collision correlation system 108. The input from aircraft model provides an indication of the possibility of recover and avoidance of collision based upon the maneuverability of the aircraft. Also determined by ground avoidance replanning system are the critical points at which recovery maneuvers must be undertaken to avoid ground collision. These critical points are then communicated to IGCAS bus 14 via output 112. Now referring to Fig. 8 where there is shown a logic flow diagram illustrating the logic utilized by ground correlation system 60. The process is started and immediately moves to block 180 where the pathway of the aircraft is mapped onto the ground. This step involves obtaining elevation data corresponding to the terrain over which the aircraft will fly resulting in a ground pathway set of data . Next the process moves on to step 182 wherein the ground pathway is normalized. More specifically, this process involves determining the highest elevation for some incremental portion of the ground pathway and subsequently designating the normalized elevation for that increment of the pathway as equal to or slightly above that of the highest elevation. This normalization also allows the system to include some margin of error into the system by adding a safety margin to the normalized pathway data. In process step 184 the collision condition correlation is performed. This process involves the correlation of the normalized pathway data and the verticle flight path data (including all projected possible flight paths) to determine if an intersection of this data exists. An intersection will indicate that a collision condition exists and appropriate warnings and mission replanning should be undertaken. In block 186 a decision is made as to whether a collision condition exists. If no collision condition exists, the process is them complete and moves on to its end in block 192. If a collision condition exists, the process moves on to replan the flight and produce predicted ground avoidance maneuvers in step 188. If mission replanning has been done but is not complete in the sense that the system is not yet confident that no collision will occur, the process then reverts back to step 180 to reinitiate the ground correlation process for the newly replanned flight path. However, if the replanning has been rechecked by the system, the process moves on to its end at 192. Referring now to Fig. 9 illustrates avoidance control and guidance system 70. As shown in this figure, avoidance control and guidance system 70 receives the ground avoidance critical point input 112 from ground correlation system 60, IGCAS control mode select input 114 from IGCAS controller 90, an aircraft state vector input from inertial navigation system 28, a flight control mode state input from flight control system 35, and a mission computer mode state input from mission computer 24. All of these inputs are utilized to provide appropriate guidance control commands to avoid possible ground collision. Contained within avoidance control and guidance system 70, is IGCAS control and guidance mode logic 122, a pitch, roll and thrust target and deviation generator 124, pitch axis control and command generator 126, roll axis control and command generator 127, and a thrust axis control and command generator 128. The first signals received by avoidance control and guidance system 70 are the flight control system mode state signal from flight control system 35, the IGCAS control mode select from IGCAS controller 90 and the mission computer state signal from mission computer 24. From these signals, IGCAS control and guidance mode logic 122 determines how much control the IGCAS system has. For example, the system can be configured such that the full control of flight activities is handled by the IGCAS system or only flight director command cues are provided to the pilots. Alternatively, the system can be configured to provide warnings and displays to alert the pilot about collision conditions and advise the pilots on avoidance maneuvers. The status of IGCAS control is communicated as an IGCAS control mode signal to a pitch, roll and thrust target and deviation generator 124 to allow it to produce appropriate control signal commands. Pitch, roll and thrust target and deviation generator 124 receives the IGCAS control mode signal along with the aircraft state vector from inertial guidance system 28 and the ground avoidance critical points signal 112. Ground avoidance critical points signal 112 are made up of the locations at which some type of evasive action must be taken. Collision avoidance control generator 124 receives these commands and determines the appropriate type of flight required to evade the possible collision with the ground. This evasive flight path or evasive maneuver as determined by collision avoidance control generator 124 is then provided to pitch axis control generator 126, roll axis control generator 127 and thrust control generator 128. Each of these systems (pitch axis control generator 126, roll axis control generator 127 and thrust control generator 128) provides the appropriate settings and commands to perform the desired evasive maneuver. Pitch axis control generator 126 and roll axis control generator 127 provides the appropriate pitch and roll commands (pitch control command 116 and roll control commands 117) to perform and cue the aforementioned evasive maneuver while thrust control generator 128 determines the appropriate thrust settings to accomplish the desired maneuver and communicates that information via thrust control command 118. These signals are then transmitted to the IGCAS flight control computer 135 and appropriate guidance systems via the IGCAS bus 14 and avionics bus 20. Referring to Fig. 10 there shown a logic flow diagram that illustrates the logic used by avoidance control and guidance system 70 to produce flight control commands which will avoid ground collision. In step 200 the process begins by determining the control mode under which the system is operating. If the IGCAS system is not coupled with the flight control computer, the process will not generate flight control command. If the system is enabled, the process moves to step 202 wherein the pitch, roll, and thrust targets and deviations are computed. This is done with information from predicted avoidance path and the inertial navigation 28. Following the computation of targets and deviations, this information can be used to generate the actual flight director commands to cue the pilot, and the flight control actuator commands to cause the aircraft to undergo evasive maneuvers. The pitch axis targets and deviations are utilized in block 204 to generate pitch axis flight director and flight control commands. Similarly, the roll axis targets and deviations are utilized in block 206 to generate roll axis flight director and flight commands. Lastly, the thrust targets and deviations are utilized in block 208 to generate thrust axis flight director and thrust control commands. Having illustrated and described the principles of the invention in the preferred embodiment it should be apparent to those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. We claim all modifications coming within the scope and spirit of the following claims.

Claims: A ground collision avoidance system for use in a high performance aircraft which has a mission control system (24), a navigation system (28), a digital terrain elevation database (32), active terrain sensors (38) and a radar altimeter (26), the ground collision avoidance system (10) comprising: a) a local terrain awareness system (40) which fuses inputs from the mission control system, the navigation system, the active terrain sensors, and the radar altimeter with terrain information in the digital terrain elevation database to generate a current profile of the elevation and character of the terrain over which the aircraft is operating; b) a flight envelope prediction system (50) attached to the mission control system for providing first and second flight envelopes, where the first envelope is an instantaneous prediction of the aircraft's path on a current flight path and the second flight envelope predicts a climb path necessary to avoid the terrain which may exist in the first envelope; c) a ground correlation system (60) attached to the local terrain awareness system and the flight envelope prediction system for correlating terrain elevation data with the first and second flight envelopes so as to provide pathway elevation data indicative of specific ground elevation data over which the aircraft travels; d) a collision control and guidance system (70) attached to the ground correlation system and the flight envelope prediction system which determines a ground collision condition exists when the generation of the second flight envelope by the flight envelope prediction system is no longer possible, and then calculates at least one standard evasive maneuver to avoid collision with the terrain; and e) a collision warning system (80) attached to the collision control and guidance system for producing an alarm if the collision condition exists. The system of claim 1, wherein the alarm system comprises a warning buzzer. The system of claim 1 or 2 comprising a display system (84) attached to the collision warning system (80) for producing a visual display capable of presenting the collision condition. The system of claim 1, 2 or 3 wherein, in response to the alarm produced by the collision warning system (80), the collision control and guidance system (70) determines a calculated evasive maneuver which, if carried out, will avoid the collision condition. The system of claim 4, wherein the calculated evasive maneuver includes a pitch control command, a roll control command and a thrust control command. The system of one of the preceding claims, further comprising an aircraft dynamics model (39) indicative of the operating dynamics of the aircraft, the aircraft dynamics model accessible by the flight prediction envelope system, the collision control and guidance system, and the collision warning system. The system of claim 6, wherein the aircraft dynamics model (39) includes aircraft response times, aircraft dynamic performance characteristics, and pilot response times. The system of one of the preceding claims, further including a flight phase monitor apparatus (56) which tracks which phase of flight the aircraft is in and provides the phase information to the flight envelope prediction system (50). A method for avoiding collision between an aircraft and the ground, comprising the steps of: a) determining the aircraft altitude and a first predicted flight envelope where the first predicted flight envelope is the aircraft's current flight path; b) generating a vertical profile which includes terrain elevations over which the aircraft is currently positioned, and the terrain elevations corresponding to the terrain over which the first predicted envelope passes, where the terrain elevations are generated from a fusion of a digital terrain elevation database and inputs from active terrain sensors, inertial navigation system, and radar altimeter; c) continually determining a second predicted flight envelope in which the aircraft climbs out of the first predicted flight envelope to avoid any collisions with the terrain; d) determining that a collision condition exists when a second predicted flight envelope cannot be generated which allows the aircraft to avoid any collisions with the terrain along the first predicted flight envelope; e) warning the pilot when a collision condition exists and determining an evasive maneuver which will avoid the collision condition; and f) presenting the evasive maneuver to the pilot via a multifunction display.

Inventors: TRAN MY, TRAN, MY
Applicants: HONEYWELL INC, HONEYWELL INC.
Application year: 1996
Main classification: G05D1
IPC codes: G08G5, G01C5, G05D1, G01S13