Abstract:
An airborne radar display is simulated using electronic messages obtained from a traffic alert and collision avoidance system (TCAS). The system does not utilize radar. Rather, the data that is received by a TCAS receiver, such as the range and bearing of other aircraft in the vicinity, are transformed into a display resembling that of a conventional airborne radar system.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to the field of aircraft radar systems and, more specifically, to simulated radar systems and methods for use in training pilots and/or radar operators in aircraft not equipped with a conventional radar system.  
       BACKGROUND OF THE INVENTION  
       [0002]     Today, many military aircraft employ on-board air-to-air and air-to-ground radar systems to provide their pilots with information, respectively, associated with other aircraft in flight and with features of the terrain being flown over. The air-to-air radar systems generally employ a tactical symbology to provide pilots with the range, bearing, and relative altitude of other aircraft on a radar display mounted in the cockpit. In addition, the air-to-air radar systems provide pilots with an indication of whether the other aircraft comprise enemy or non-enemy aircraft. The air-to-ground radar systems typically provide pilots with information related to terrain features being flown over. Such information includes the range, bearing, and altitude of various terrain features and different symbols associated with different types of terrain features.  
         [0003]     The air-to-air and air-to-ground radar systems on an aircraft generally consume substantial physical space inside the cockpit of the aircraft for electronic components and utilize one or more antennae that are mounted in the aircraft&#39;s nose behind a protective nose cone. On many aircraft, the consumption of space for such radar systems is not an issue. However, on many aircraft used for training, physical space is at a premium and there is often not enough available space for such radar systems. As a consequence, many training aircraft are not fitted with such radar systems, thereby making it difficult for pilots in training to receive a substantial amount of flight time in aircraft equipped with such radar systems. Further, air-to-air and air-to-ground radar systems are generally costly and it is fiscally unfeasible to equip every training aircraft with such radar systems, even if sufficient physical space is available. Therefore, in order to receive sufficient training in the use of such radar systems, pilots in training must spend substantial time in expensive ground-based aircraft simulators having simulated air-to-air and air-to-ground radar systems.  
         [0004]     Fortunately, however, many training aircraft are equipped with a Traffic Alert and Collision Avoidance System (“TCAS”) that provides pilots with visible and audible alerts and other information related to nearby aircraft that may pose a threat for a mid-air collision.  FIG. 1  is a generalized block diagram representation of a conventional TCAS as known in the prior art. The TCAS generally comprises a controller that is connected to omni-directional and directional antennae in order to collect data corresponding to the range and bearing of such other aircraft. The TCAS controller is also connected to one or more control(s) that enable a pilot to select a range for the display of data related to aircraft features within such range. The TCAS controller is additionally connected to a display for the display of such data. Generally, during operation, the TCAS controller generates a TCAS display message for each nearby aircraft, including its range and bearing, that is communicated to the display via a communication link between the TCAS controller and display. Using the data present in the TCAS display message, the display presents an image using symbols to display such aircraft to pilots.  
         [0005]     While TCAS provides pilots with information related to other aircraft that is similar to that provided by on-board air-to-air radar systems and enables pilots in training to become somewhat familiar with viewing displays containing information related to other aircraft, TCAS does not provide the tactical and other information provided to pilots by a typical military air-to-air or radar system. Thus, unfortunately, TCAS cannot supplant on-board military radar systems in military aircraft and cannot be employed alone in training aircraft to train military pilots in the use of military radar systems.  
         [0006]     Therefore, there exists in the industry, a need for a relatively inexpensive simulated radar system having air-to-air and air-to-ground capabilities that addresses these and other problems or difficulties that exist now or in the future.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention relates to simulating airborne radar using electronic messages obtained from a traffic alert and collision avoidance system (TCAS). The invention simulates the display of a conventional air-to-air or, alternatively or in addition, air-to-ground airborne radar system but does not utilize radar. Rather, the data that is received by a TCAS receiver in the conventional manner, such as the range and bearing of other aircraft in the vicinity, are transformed into a display resembling that of a conventional airborne radar system. For example, in an-air-to-air embodiment, data representing such other aircraft can be displayed using the tactical military symbology that is standard in military airborne radar instead of using TCAS symbology. In an air-to-ground embodiment, a representation of the terrain over which the aircraft is flying can be displayed. Embodiments of the invention can include both an air-to-air mode and an air-to-ground mode, with the mode selectable by the pilot or other user. A terrain map can be stored in a suitable digital storage device integrated with the simulated radar system. The invention can be used, for example, to train student pilots in the use of radar in training aircraft that do not have radar. Other advantages and benefits of the present invention will become apparent upon reading and understanding the present specification when taken in conjunction with the appended drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a block diagram representation of an aircraft traffic alert and collision avoidance system (TCAS) in accordance with the prior art.  
         [0009]      FIG. 2  is a block diagram representation of a simulated radar system in accordance with an exemplary embodiment of the present invention.  
         [0010]      FIGS. 3A-3C  are flowchart representations, in accordance with the exemplary embodiment of the present invention, of a method for providing simulated air-to-air and air-to-ground radar for training pilots and/or radar operators.  
         [0011]      FIG. 4  is a flowchart representation of a target data generation method, in accordance with the exemplary embodiment of the present invention, for producing and storing target data associated with aircraft detected by an aircraft traffic alert and collision avoidance system.  
         [0012]      FIG. 5  is a flowchart representation of a target display data generation method, in accordance with the exemplary embodiment of the present invention, for generating target display data associated with aircraft detected an aircraft traffic alert and collision avoidance system.  
         [0013]      FIG. 6  is a flowchart representation of a terrain display data generation method, in accordance with the exemplary embodiment of the present invention, for generating terrain display data associated with overflown or nearby terrain. 
     
    
     DETAILED DESCRIPTION  
       [0014]     Referring now to the drawings in which like numerals represent like elements or steps throughout the several views,  FIG. 2  is a block diagram representation of a simulated radar system  100  in accordance with an exemplary embodiment of the present invention. The simulated radar system  100  generally resides within an aircraft used for pilot training (not shown for purposes of clarity) and receives data from the aircraft&#39;s traffic alert and collision avoidance system (sometimes referred to herein as “TCAS”). The simulated radar system  100  is operable in at least two operation modes, including without limitation, an air-to-air mode and an air-to-ground mode. In the air-to-air operation mode, the simulated radar system  100  provides a simulated radar display using tactical symbology that is created from data received from the traffic alert and collision avoidance system. In the air-to-ground operation mode, the simulated radar system  100  provides a simulated terrain display of nearby terrain using appropriate symbology that is based on terrain map data stored on a data storage media. Because the simulated radar system  100  utilizes data from the aircraft&#39;s traffic alert and collision avoidance system and from a data storage media to produce displays simulating those of conventional aircraft radar systems without the bulky, space-consuming electronic components and radar antenna of such conventional radar systems, the simulated radar system  100  may be installed and used in the cockpit of training aircraft that do not have sufficient space available for a conventional radar system.  
         [0015]     The simulated radar system  100  is, as illustrated in  FIG. 2 , communicatively connected to an aircraft&#39;s traffic alert and collision avoidance system when installed in an aircraft by communication link  102  for the receipt of messages therefrom. More particularly, communication link  102  is connected (i.e., in a tap-like manner) to a communication link of the aircraft&#39;s traffic alert and collision avoidance system that extends between a controller and display thereof. Through such connection and communication link  102 , the simulated radar system  100  receives each message that is communicated between the TCAS controller and display via the communication link extending therebetween. Because such messages may include messages having data associated with aircraft representations for display by the TCAS display (sometimes referred to herein as “TCAS display messages”) as well as other messages and because the simulated radar system  100  utilizes the data present in such TCAS display messages to produce its simulated radar display in air-to-air operation mode, the simulated radar system  100  determines, as described below, which received messages constitute TCAS display messages and which received messages constitute other TCAS messages. The simulated radar system  100  disregards TCAS messages that do not constitute TCAS display messages.  
         [0016]     The simulated radar system  100  is also communicatively connected, via communication link  104 , to another aircraft system that is adapted to provide position data to the simulated radar system  100  corresponding to the position of the aircraft. Such other aircraft system may comprise, for example, a global position satellite system (“GPSS”) that continually determines and provides position data for the aircraft to the simulated radar system  100 . The position data received from such other aircraft system via communication link  104  is utilized by the simulated radar system  100  when operating in air-to-ground mode to determine which terrain features of the terrain map data are within a display range selected by a pilot or other user of the simulated radar system  100 . Such terrain features are displayed by the simulated radar system  100 .  
         [0017]     As illustrated in  FIG. 2 , the simulated radar system  100  comprises a controller  106 , a display  108 , a plurality of controls  110 , and a data storage device  112  storing terrain map data. The controller  106  is connected, when installed in an aircraft, to communication links  102 ,  104  for the receipt, respectively, of TCAS messages and aircraft position data. The controller  106  is connected to the display  108  through communication link  114  for the communication of display data from the controller  106  to the display  108 . Such display data may comprise data corresponding to other aircraft when the simulated radar system  100  is operating in air-to-air operation mode and data corresponding to terrain features when the simulated radar system  100  is operating in air-to-ground operation mode.  
         [0018]     Generally, the display data corresponding to other aircraft includes data representative of each aircraft that is within a desired display range and may include, for example, data related to (a) the other aircraft&#39;s position relative to the aircraft in which the simulated radar system  100  is present (sometimes referred to herein as the “training aircraft”), (b) the other aircraft&#39;s heading (e.g., bearing), speed, altitude, rate of climb or descent, (c) the other aircraft&#39;s status as a “friend” or “foe”, and/or (d) other tactical information related to the other aircraft. The display data corresponding to other aircraft is typically in a form that enables the display  108  to represent the other aircraft using tactical symbology employed by conventional military radar systems. It should be noted, however, that the scope of the present invention encompasses display data corresponding to other aircraft that enables the display  108  to represent such other aircraft using non-tactical symbology or symbology utilized by the radar systems of commercial aircraft.  
         [0019]     The display data corresponding to terrain features typically includes data representative of each terrain feature of the terrain map data that is within a desired display range of the training aircraft such that a pilot or radar operator may identify the terrain features when such data is displayed by display  108  in air-to-ground mode. Such display data is generally in a form that enables the display  108  to represent the terrain features using an appropriate symbology and may include data related to, for example, (a) the position and altitude of various mountains, hills, rivers, streams, and other landmarks, (b) the position of potential enemy targets, (c) the position of friendly installations, and/or (d) other information related to terrain features.  
         [0020]     The display  108  is adapted to produce images representative of display data received from the controller  106  through communication link  114 . Generally, the display  108  comprises a flat panel display that is operable to receive and produce an image from display data in raster form. It should be understood, however, that the scope of the present invention includes simulated radar systems  100  having other types of displays  108  or displays  108  that utilize other display technologies.  
         [0021]     It should be noted that in an exemplary embodiment of the invention both the simulated radar system  100  as illustrated in  FIG. 2  and a conventional TCAS as illustrated in  FIG. 1  reside in the same training aircraft. Thus, the pilot or student pilot can view both the display  108  of the simulated radar system  100  as well as the conventional TCAS display. It should be noted that in some implementations the display  108  may serve two functions and may alternatively be used to display simulated radar data or TCAS data.  
         [0022]     The controller  106  is also connected to the plurality of controls  110  by communication links  116  such that the controller  106  may determine or read the current settings of the controls  110 . Generally, the controls  110  comprise input devices that enable a pilot or radar operator to provide inputs to the simulated radar system  100 . One such control  110 A comprises an operation mode selector that is used by a pilot or radar operator to select an operation mode for the simulated radar system  100 . Control  110 A is movable between a first position in which the air-to-air operation mode is selected and a second position in which the air-to-ground operation mode is selected. Another such control  110 B comprises a range selector that is used by a pilot or radar operator to select a range or distance within which the simulated radar system  100  will display representations of and information related to other aircraft (i.e., if the simulated radar system  100  is in air-to-air mode) or to nearby terrain features (i.e., if the simulated radar system  100  is in air-to-ground mode). Control  110 B is movable between a plurality of positions corresponding to respective display ranges. Exemplary ranges or distances might include 25 miles, 50 miles, or 100 miles. Generally, the controls  110  comprise switches that may be manually positioned by a pilot or radar operator. However, many other forms of controls  110  might be employed (including, without limitation, on-screen controls or buttons) within the scope of the present invention.  
         [0023]     Preferably, the user interface effected by the combination of the controller  106 , display  108  and controls  100  mimics or simulates the user interface of a specific radar system. For example, the display symbology, type and layout of controls, and other characteristics of a radar user interface typically vary among radar system products, as each manufacturer produces radar systems having characteristics unique to that manufacturer or product line. Indeed, many such products have a distinctive “look and feel” associated with the manufacturer or product line. Thus, the user interface effected by the combination of the controller  106 , display  108  and controls  100  can simulate that of a specific product with which it is desired for the student pilot to become familiar.  
         [0024]     The controller  106  is additionally connected to the data storage device  112  via communication link  118  for the communication of commands and other signals to the data storage device  112  requesting terrain map data and for the receipt of terrain map data stored on the data storage device  112 . Generally, the data storage device  112  comprises an optical disk drive having a removable media storing terrain map data thereon that is representative of the terrain to be simulatively overflown during a training session using the simulated radar system  100 . Thus, different removable media may be employed to enable training sessions that simulate the overflight of different terrain. The data storage device  112  may communicate terrain map data to the controller  106  in streaming video form or in non-streaming video form. Further, it should be noted that data storage device  112  may comprise any device adapted to store terrain map data, to receive requests for desired terrain map data from the controller  106 , to retrieve such desired terrain map data, and to provide such desired terrain map data to the controller  106 . Therefore, the data storage device  112  may comprise, for example and not limitation, flash memory, random access memory, read-only memory, programmable read-only memory, other electronic storage devices, magnetic disk drive(s), magneto-optical disk drive(s), other devices having removable or non-removable media, and/or other devices or combination(s) thereof.  
         [0025]     The controller  106  generally comprises one or more microprocessor(s), memory, and one or more communication interfaces to receive TCAS messages from the aircraft&#39;s TCAS via communication link  102 , to receive position data corresponding to the position of the aircraft via communication link  104 , and to communicate commands, data, and/or signals with the display  108 , controls  110 , and data storage device  112  via respective communication links  114 ,  116 ,  118 . The memory is configured with a plurality of software program instructions that are executable by the one or more microprocessor(s) to cause the simulated radar system  100  to operate in accordance with the methods described herein. The memory is also adapted to store intermediate and/or temporary data that may be generated during execution of the software program instructions and during operation of the simulated radar system  100 . Such intermediate data includes target data corresponding to potential radar targets in air-to-air operation mode that is stored in an area of memory referred to herein as target data memory. Such intermediate data further includes display data for display on display  108  that is stored in a different area of memory referred to herein as display memory. Typically, the memory comprises flash memory and random access memory, but may include other forms of memory or other devices for storing data.  
         [0026]     The software program instructions of the controller  106  are organized into a main program, a target data generation routine, a target display data generation routine, a terrain display data generation routine, and a display routine. The main program, when executed by a controller microprocessor, controls the overall operation of the simulated radar system  100  according to a method  300  of providing simulated air-to-air and/or air-to-ground radar for training pilots and/or radar operators. The target data generation routine is executed by a controller microprocessor when control  110 A (e.g., the operation mode selector) is positioned in the position corresponding to the air-to-air operation mode. When executed by a controller microprocessor, the target data generation routine causes the simulated radar system  100  to operate in accordance with a target data generation method  400  that monitors TCAS messages for TCAS display messages, produces target data from information extracted from the TCAS display messages, and stores the target data in target data memory. The target display data generation routine is also executed by a controller microprocessor when control  110 A is positioned in the position corresponding to the air-to-air operation mode. When executed, the target display data generation routine causes the simulated radar system  100  to operate according to a target display data generation method  500  that retrieves target data from target data memory, determines whether the retrieved target data is within a desired display range as indicated by the then current position of control  110 B (e.g., the range selector), generates target display data for radar targets within such desired display range using tactical radar symbology appropriate for each radar target, and stores the generated target display data in display memory.  
         [0027]     The terrain display data generation routine is executed by a controller microprocessor when control  110 A (e.g., the operation mode selector) is positioned in the position corresponding to the air-to-ground operation mode. When executed by a controller microprocessor, the terrain display data generation routine causes the simulated radar system  100  to operate in accordance with a terrain display data generation method  600  that retrieves terrain map data from data storage device  112  that is within a desired display range (e.g., as indicated by the then current position of control  110 B) of the aircraft&#39;s then current position, generates terrain display data for such retrieved terrain map data using symbology appropriate for the various terrain features, and stores the generated terrain display data in display memory.  
         [0028]     The display routine is generally executed by a controller microprocessor on a continual basis regardless of whether control  110  is positioned in the position corresponding to the air-to-air operation mode or in the position corresponding to the air-to-ground operation mode. During execution, the display routine causes the simulated radar system  100  to operate according to a display method that retrieves display data from display memory and communicates the retrieved display data to the system&#39;s display  108  via communication link  114 . One of ordinary skill in the art should be familiar with such display methods and, therefore, the display routine is not described herein in further detail.  
         [0029]      FIGS. 3A-3C  together provide a flowchart representation, in accordance with the exemplary embodiment of the present invention, of a method  300  for providing simulated air-to-air and air-to-ground radar for training pilots and/or radar operators. After starting at step  302 , method  300  advances to step  304  where the controller  106  determines the currently desired operation mode of the simulated radar system  100  by reading the position of control  110 A (e.g., the operation mode selector). Then, at step  306 , the controller  106  sets (e.g., establishes and stores) intermediate operation mode data in the controller&#39;s memory to correspond to the read position setting of control  110 A. Proceeding to step  308  of method  300 , the controller  106  determines the currently desired display range for target and/or terrain map data to be displayed via the simulated radar system  100  by reading the position of control  110 B (e.g., the range selector). After reading the position of control  110 B, the controller  106  sets (e.g., establishes and stores) intermediate range data in the controller&#39;s memory, at step  310 , to correspond to the read position setting of control  110 B.  
         [0030]     At step  312  of method  300 , the controller  106  ascertains whether the operation mode is set to air-to-air mode or air-to-ground mode by retrieving and analyzing the intermediate operation mode data stored in the controller&#39;s memory. If the operation mode is set to air-to-air mode, the controller  106  advances to step  314  where it initiates execution of the target data generation routine. Then, at step  316 , the controller  106  initiates execution of the target display data generation routine. Upon such initiation, the controller  106  proceeds to step  320  of method  300  described below. If, at step  312 , the controller  106  ascertains that the operation mode is set to air-to-ground mode, then the controller  106  initiates execution of the terrain display data generation routine at step  318  before moving to step  320  of method  300 .  
         [0031]     The controller  106  begins a loop of operation at step  320  by once again determining the currently desired operation mode of the simulated radar system  100  by reading the position of control  110 A (e.g., the operation mode selector). Then, at step  322 , the controller  106  decides whether the desired operation mode of the simulated radar system  100  has been changed by a pilot and/or radar operator since the last pass through the loop. The controller  106  generally makes such decision by comparing the position of control  110 A read at step  320  with the intermediate operation mode data stored in the controller&#39;s memory. If the controller  106  decides that the position of control  110 A corresponds to the intermediate operation mode data, then no change in operation mode has occurred since the last pass through the loop and the controller  106  advances to step  340  of method  300  described below. If the controller  106  decides that the position of control  110 A does not correspond to the intermediate operation mode data, then at step  324  the controller  106  sets (e.g., establishes and stores) the intermediate operation mode data in the controller&#39;s memory to correspond to the position setting of control  110 A read at step  320 .  
         [0032]     Continuing at step  326  of method  300 , the controller  106  ascertains whether the operation mode is set to air-to-air mode or air-to-ground mode by retrieving and analyzing the intermediate operation mode data stored in the controller&#39;s memory. If the operation mode is set to air-to-air mode, the controller  106  advances to step  328  where it terminates execution of the terrain display data generation routine since the operation mode was formerly air-to-ground mode and since the terrain display data generation routine would be executing in such mode. Then, the controller  106  initiates execution of the target data generation routine at step  330  and initiates execution of the target display data generation routine at step  332 . After initiating these routines, the controller  106  moves ahead to operate in accordance with step  340  described below.  
         [0033]     If, at step  326 , the controller  106  ascertains that the operation mode is set to air-to-ground mode, the controller  106  proceeds to step  334  of method  300  where it terminates execution of the target data generation routine and subsequently to step  336  where it terminates execution of the target display data generation routine. The terminations of these routines are made since the operation mode was formerly air-to-air mode and since the target data generation routine and target display data generation routine would be executing in such mode. Then, the controller  106  moves to step  338  where it initiates execution of the terrain display data generation routine before advancing to step  340  described below.  
         [0034]     At step  340  of method  300 , the controller  106  determines the currently desired display range for target and/or terrain map data to be displayed via the simulated radar system  100  by reading the position of control  110 B (e.g., the range selector). After reading the position of control  110 B, the controller  106  decides at step  342  whether the desired display range of the simulated radar system  100  has been changed by a pilot and/or radar operator since the last pass through the loop. The controller  106  generally makes such decision by comparing the position of control  110 B read at step  340  with the intermediate range data stored in the controller&#39;s memory. If the controller  106  decides that the position of control  110 B corresponds to the intermediate range data, then no change in operation mode has occurred since the last pass through the loop and the controller  106  loops back to step  320  of method  300  described above. If the controller  106  decides that the position of control  110 B does not correspond to the intermediate range data, then at step  344  the controller  106  sets (e.g., establishes and stores) the intermediate range data in the controller&#39;s memory to correspond to the position setting of control  110 B read at step  340 .  
         [0035]     After setting the intermediate range data, the controller  106  ascertains at step  346  whether the operation mode is set to air-to-air mode or air-to-ground mode by retrieving and analyzing the intermediate operation mode data stored in the controller&#39;s memory. If the operation mode is set to air-to-air mode, the controller  106  advances to step  348  where it terminates execution of the target display data generation routine. Then, at step  350 , the controller  106  initiates execution of the target display data generation routine. By first terminating execution of the target display generation routine and then re-initiating its execution, the controller  106  causes the display of radar target data to be reset for the currently desired display range. Once execution of the target display data generation routine is re-initiated, the controller  106  loops back to operate according to step  320  of method  300 .  
         [0036]     If, at step  346 , the controller  106  ascertains that the operation mode is set to air-to-ground mode, the controller  106  proceeds to step  352  where it terminates execution of the terrain display data generation routine. The controller  106  then, at step  354 , re-initiates execution of the terrain display data generation routine. Through the termination and re-initiation of the terrain display data generation routine, the controller  106  causes the display of terrain map data to be reset for the currently desired display range. After re-initiating execution of the terrain display data generation routine, the controller  106  returns to step  320  of method  300  where it once again determines the currently desired operation mode of the simulated radar system  100 .  
         [0037]      FIG. 4  is a flowchart representation of a target data generation method  400 , in accordance with the exemplary embodiment of the present invention, for producing and storing target data respectively associated with aircraft detected by the training aircraft&#39;s TCAS. The target data is produced from data collected from intercepted TCAS display messages and is stored in the controller&#39;s target data memory. After starting at step  402 , the method  400  advances to step  404  where the controller  106  clears the target data memory. Then, at step  406 , the controller  106  receives a TCAS message from the aircraft&#39;s TCAS via communication link  102 . Generally, the TCAS messages so received constitute TCAS display messages having data respectively associated with aircraft detected by the aircraft&#39;s TCAS, but may conceivably constitute other types of TCAS messages. Therefore, at step  408 , the controller  106  determines whether the received TCAS message constitutes a TCAS display message. If not, the controller  106  loops back to step  406  to receive another TCAS message.  
         [0038]     If, at step  408 , the controller  106  determines that the received TCAS message is a TCAS display message, the controller  106  advances to step  410  of method  400  where it extracts data from the TCAS display message. Such data (sometimes referred to herein as “target data”) includes, for example and not limitation, data defining the identity, range, bearing, and altitude of the aircraft associated with the received TCAS display message. Proceeding to step  412 , the controller  106  ascertains whether the aircraft associated with the received TCAS display message (sometimes referred to herein as a “target”) constitutes a new target for the simulated radar system  100 . The controller  106  does so by comparing the identity data for the target associated with the received TCAS display message to the identity data associated with targets already present in the controller&#39;s target data memory. If the identity data for the target associated with the received TCAS display message is not present in the target data memory, then the target is a new one and the controller  106  moves to step  414  of method  400  where it saves the target data for the target in the controller&#39;s target data memory. Then, the controller  106  returns to step  406  to receive another TCAS message via communication link  102 .  
         [0039]     If the controller  106  ascertained, at step  412 , that the aircraft associated with the received TCAS display message is not a new target for the simulated radar system  100 , then the controller  106  advances to step  416  of method  400  where it calculates target speed and heading by comparing current range and bearing data with previous values. The controller  106  then advances to step  418  of method  400  updates the already present target data for the target in the controller&#39;s target data memory with the target data newly received in the TCAS display message. After updating the target data, the controller  106  loops back to step  406  to receive another TCAS message from the aircraft&#39;s TCAS through communication link  102 .  
         [0040]      FIG. 5  is a flowchart representation of a target display data generation method  500 , in accordance with the exemplary embodiment of the present invention, for generating target display data respectively associated with aircraft detected by the training aircraft&#39;s TCAS. After starting at step  502 , the method  500  advances to step  504  where the controller  106  clears the display memory. Then, at step  506 , the controller  106  retrieves the intermediate range data stored in the controller&#39;s memory. The controller  106  next retrieves target data associated with the first target in the target data memory at step  508 .  
         [0041]     Continuing at step  510 , the controller  106  determines whether the target associated with the retrieved target data is within the desired display range for the simulated radar system  100  corresponding to the intermediate range data retrieved at step  506 . The controller  106  does so by using the retrieved target data to calculate the range, or distance, of the target from the training aircraft and by comparing the calculated range, or distance, to the range corresponding to the intermediate range data. If the controller  106  determines that the target is not within the desired display range, the controller  106  branches to step  512  of method  500  described below. If, alternatively, the controller  106  determines at step  510  that the target is within the desired display range, then at step  511  controller  106  generates display data for the target (sometimes referred to herein as “target display data”) using the target data for the target and employing tactical radar symbology. Thus, based on the identity data found in the target data for the target, the controller  106  may produce target display data that includes an identification of the radar target as a “friend” or “foe”. Then, at step  513 , the controller  106  writes or communicates the generated target display data to the controller&#39;s display memory.  
         [0042]     At step  512 , the controller  106  decides whether it has retrieved target data for the last target having target data stored in the target data memory. If so, the controller  106  returns to step  504  to once again clear the display memory (i.e., which is necessary as existing targets may move in and out of the desired display range and new targets may move into the desired display range). If not, the controller  106  retrieves the target data associated with the next target having target data stored in the target data memory at step  514 . Then, the controller  106  continues operation according to method  500  by looping back to step  510  to determine whether the next target is within the desired display range for the simulated radar system  100 .  
         [0043]      FIG. 6  is a flowchart representation of a terrain display data generation method  600 , according to the exemplary embodiment of the present invention, for generating terrain display data associated with the terrain being overflown or near the then current location of the training aircraft. After starting at step  602 , the method  600  advances to step  604  where the controller  106  clears the display memory. Then, at step  606 , the controller  106  retrieves the intermediate range data stored in the controller&#39;s memory. The controller  106  next determines the current position of the training aircraft at step  608 . To do so, the controller  106  generally utilizes the position data for the training aircraft received from another aircraft system via communication link  104 .  
         [0044]     Next, at step  610 , the controller  106  retrieves terrain map data from data storage device  112  via communication link  118  that is within the range, or distance, identified by the intermediate range data from the training aircraft&#39;s current position. The controller  106 , at step  612 , subsequently generates display data for the terrain using the retrieved terrain map data and symbology that is appropriate for the various features of the terrain. Then, at step  614 , the controller  106  writes or stores the generated display data to the controller&#39;s display memory. After storing the display data, the controller  106  loops back to step  604  of method  600  to again clear the display memory and regenerate display data since the current position of the training aircraft will be different.  
         [0045]     Whereas this invention has been described in detail with particular reference to an exemplary embodiment and variations thereof, it is understood that other variations and modifications can be effected within the scope and spirit of the invention, as described herein before and as defined in the appended claims.