Abstract:
Systems and methods for providing the crew of a vehicle with a potential collision alert. The alert is based on presumed flight-crew action and reaction times, ownship speed, and required distance to safely stop the ownship before intersection with traffic. An exemplary system located aboard an ownship includes a communication device that receives information from a ground traffic; a memory device that stores ownship information and predefined constants; and a processing device that determines a distance to the traffic when the traffic passes the ownship after the ownship stops at a estimated full-stop location, based on the received ownship information and the predefined constants, determines distance to the ground traffic vehicle, based on the determined point in time, and generates a potential collision alert if the determined distance is less than a predefined safe distance value. An exterior lighting device outputs a visual illumination after the potential collision alert is generated.

Description:
BACKGROUND OF THE INVENTION 
     There exists a significant problem with potential collisions between aircraft (or ground vehicles) and other aircraft (or ground vehicles) during operations on the surface of the airport, particularly at night or in low-visibility conditions. 
     Current collision-avoidance systems, such as traffic collision avoidance systems (TCAS) are effective only when aircraft are airborne. Also, relatively few large airports are equipped with radar that can monitor surface traffic, and even where it is available this radar usually has many “blind spots” on the airport where detection of airplanes or vehicles is not possible. 
     SUMMARY OF THE INVENTION 
     The present invention includes systems and methods for providing the crew of an airplane or vehicle with an alert of an impending collision. 
     The time when the alert is triggered depends on presumed flight-crew action and reaction times, ownship speed, and required distance to safely stop the ownship before intersection with traffic. Moreover, the present invention does not use airport map data. 
     An exemplary system located aboard an ownship includes a communication device that receives information from a ground traffic vehicle; a memory device that stores ownship information and predefined constants; and a processing device that determines a point in time associated with a full-stop location of the ownship, based on the received ownship information and the predefined constants, determines distance to the ground traffic vehicle based on the determined point in time, and generates a potential collision alert if the determined distance is less than a predefined safe distance value. An output device outputs the generated potential collision alert. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings: 
         FIG. 1  is a block diagram of an exemplary system formed in accordance with an embodiment of the present invention; 
         FIG. 2  is a perspective view of an aircraft illuminating another aircraft during a potential collision condition; 
         FIG. 3  is a flow diagram of an exemplary process performed by the present invention; 
         FIG. 4  is a top-down view of two aircraft taxiing on crossing trajectories; 
         FIG. 5  is a graph of the situation shown in  FIG. 4 ; and 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention identifies potential collision with traffic in sufficient time to allow the crew to take corrective action. The present invention also ensures that nuisance alerts or lost alerts are minimized. The present invention does not rely on the availability of map data for the airport. 
       FIG. 1  shows an exemplary system  20  located on an ownship (e.g., aircraft, airport ground vehicle)  18  for providing a crew of the ownship ample early warning of a potential ground operations collision. The system  20  includes a processor  24  that is in signal communication with a data communication device  28 , memory  30  (i.e., database), an output device  32 , a navigation/position device  34  (e.g., GPS, INS, etc.) and an interface (IF) device  36 . 
     The processor  24  receives the following data from existing avionic systems on the ownship  18 :
         Geographic Position (latitude and longitude from the positioning device  34 );   Heading (from the heading reference system  38  (e.g., gyro, compass, inertial navigation system (INS));   Speed (from the positioning device  34 ); and   Wingspan information (from the memory  30 ).       

     The processor  24  receives the following data from other aircraft or vehicles (the “traffic”):
         Geographic Position (latitude and longitude);   Heading;   Speed; and   Size Category.       

     An example of the data communications device  28  includes an automatic dependent surveillance-broadcast (ADS-B) data link system. 
     The processor  24  also receives from the memory  30 , or some external source, some constant values, such as those previously defined in various publications (e.g., RTCA DO-322). Examples of constant values include:
         Flight crew reaction time t R  (seconds)—time to alert notice and evaluation;   Flight crew action time t A  (seconds)—time of decision making and starting a braking action;   Aircraft “standard” deceleration a (meters/second)—rate of deceleration while braking following an alert.       

     Using all or a portion of the received data, the processor  24  determines if a collision-alert condition exists. If a collision-alert condition is determined to exist, the processor  24  outputs an alert signal to the output device  32 . 
       FIG. 2  shows a first taxiing aircraft  50  that has determined that a potential collision condition exists with a second taxiing aircraft  54 . In response to the potential collision condition determination, the first taxiing aircraft  50  activates lights  40  (e.g., landing lights) that provide illumination in the direction of the second taxiing aircraft  54 , thus alerting the second aircraft&#39;s flight crew of an alert condition. 
       FIG. 3  shows a flow diagram of an exemplary process  60  performed by the system  20 . First, at a decision block  64 , the processor  24  determines if the ownship is on the ground. If the ownship is a ground vehicle, then this condition is always true. If the ownship is an aircraft, then the processor  24  determines this condition to be true, based on an on-ground indicator (e.g., weight-on-wheels signal) received from a databus via the IF device  36 , ownship position and altitude information, airport/geographic information (i.e., altitude), or some other criteria. 
     After the ownship is determined to be on the ground, the processor  24  receives information from other proximate grounded vehicles at process  68 . Then, the process  60  determines if the ownship is moving, see decision block  70 . If the ownship is determined to be moving, the process  60  determines if a potential collision condition exists, based on the received target information and the ownship information, see decision block  72 . If the potential collision condition does not exist, then the process  60  returns to decision block  64  after a delay (block  74 ). If the potential collision condition exists, then, at a block  76 , a distance to the traffic, when the traffic will pass the ownship after an estimated ownship stopping position, is determined. 
     Next, at a decision block  80 , it is determined if the determined distance to the traffic is less than or equal to a predetermined safe-distance value. If the distance to traffic is not less than or equal to the predetermined safe-distance value, then the process  60  returns to decision block  64 . If the distance to traffic is less than or equal to the predetermined safe-distance value, then, at a block  82 , a potential collision alert condition exists and warning of the traffic is performed by illuminating an exterior light  40  of the ownship. The illuminated exterior light of the ownship provides a warning to the flight crew of the traffic that a collision threat exists. At a decision block  86 , after a delay the process  60  determines if the potential collision alert condition still exists. If the potential collision alert condition still exists, then at a block  88 , the illumination of the exterior light(s) is changed (e.g., steady to flashing; slow flashing to fast flashing). If the potential collision alert condition is determined to not exist after the delay, then at a block  90 , the exterior light(s) is extinguished. 
     The exterior light is one designated exclusively for this purpose or is an existing light(s) of the ownship (e.g. landing lights). 
     In one embodiment, the first time the exterior light(s) is illuminated, it is illuminated in a predefined pattern. An example of the predefined pattern includes steady on at various levels of intensity. Another example of the predefined pattern includes flashing at a first rate. 
     When the exterior light(s) illumination is changed, various aspects of the illuminating exterior light(s) are changed either separately or in combination. For example, the light intensity changes, the rate of flashing changes or if there are more than one landing light, then the lights alternately flash. If the potential collision alert condition still existed after the delay without adequate resolution, it would be assumed that a collision is more imminent. In this situation, the exterior light illumination is changed in order to impart a more immediate need to take action. Increasing the flash rate or intensity of the exterior light(s) are exemplary ways of imparting a need to take action. 
     In one embodiment, the outputted alerts include graphical highlighting of areas or traffic on a cockpit map display, are text messages presented on a display, or are aural messages provided to the crew via cockpit loudspeaker or headset. Tactile alert systems may also be used. 
     The solution of the potential traffic collision detection is built on the following conditions:
         Ownship is aware about the traffic position (e.g., from traffic ADS-B data or another source);   Ownship is aware about the traffic heading (e.g., from traffic ADS-B data or another source);   Ownship is aware about the traffic speed (e.g., from traffic ADS-B data or another source); and   Ownship is aware about the traffic size category (e.g., from traffic ADS-B data or another source).       

     Wingspan of the traffic is determined according to information about the size category of the traffic aircraft, e.g., from the traffic ADS-B data and a database stored in the memory  30 . For each size category, the processor  24  uses the higher value of wingspan range stored in the memory  30 . 
     The processor  24  uses the following constants when determining the full-stop location: flight crew reaction time (t R  (sec)); flight crew action time (t A  (sec)); and aircraft deceleration (a(′s 2 )). 
     Based on speed of the ownship (OS) the braking distance (d Brake ) and time to full stop (T STOP ) are calculated from following formulas: 
     
       
         
           
             
               
                 
                   
                     t 
                     S 
                   
                   = 
                   
                     
                       V 
                       OS 
                     
                     
                        
                       a 
                        
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   
                     T 
                     STOP 
                   
                   = 
                   
                     
                       t 
                       R 
                     
                     + 
                     
                       t 
                       A 
                     
                     + 
                     
                       t 
                       S 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   
                     d 
                     Brake 
                   
                   = 
                   
                     
                       
                         v 
                         OS 
                       
                       · 
                       
                         T 
                         STOP 
                       
                     
                     + 
                     
                       
                         1 
                         2 
                       
                       ⁢ 
                       
                         a 
                         . 
                         
                           t 
                           S 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
         
         
           
             where (t s ) is time of ownship deceleration to full stop from (v OS ) (actual speed of ownship) without consideration of crew reaction or action time. 
           
         
       
    
     Equation (3) represents the assumption that, after alert triggering, the speed of ownship remains constant during the time period (t R +t A ) and after this time ownship starts deceleration with deceleration rate (a) (ownship decelerates until v OS =0). 
     The processor  24  calculates “safe distance”. D Safe , which represents minimum distance between ownship and traffic (TR), in which ownship and traffic shall pass each other. 
     Where: C Safe —Safety coefficient;
         W Span     —     TR —wingspan of the traffic;   W Span     —     OS —wingspan of the ownship;   (retrieved from ownship parameters database (the memory  30 )).       

     
       
         
           
             
               
                 
                   
                     D 
                     Safe 
                   
                   = 
                   
                     
                       C 
                       Safe 
                     
                     · 
                     
                       
                         
                           W 
                           
                             Span 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             _ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             OS 
                           
                         
                         + 
                         
                           W 
                           
                             Span 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             _ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             TR 
                           
                         
                       
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     The processor  24  recalculates the position of traffic (X TR ; Y TR ) to a “local” coordinate system relative to the position of ownship ( FIG. 4 ). 
     GPS position of ownship: (X OS GPS ; Y OS GPS )
         X OS GPS =OS Longitude   Y OS GPS =OS Latitude       

     GPS position of Traffic: (X TR GPS ; Y TR GPS )
         X TR GPS =TR Longitude   Y TR GPS =T R  Latitude       

     Current position of ownship and traffic in the local coordinate system (expressed in feet) is as follows:
         OS position (X OS ; Y OS ): (0; 0)   TR position [X TR ; Y TR ]: (X TR GPS −X OS GPS ; Y TR GPS −Y OS GPS )       

     The processor  24  evaluates whether the traffic represents a potential threat to ownship. Evaluation is based the following values:
         actual value of traffic heading;   actual value of traffic speed;   actual value of ownship heading; and   actual value of ownship speed.       

     The current distance between ownship and traffic is expressed as follows:
 
 D   Curr =√{square root over (( X   TR   −X   OS ) 2 +( Y   TR   −Y   OS ) 2 )}{square root over (( X   TR   −X   OS ) 2 +( Y   TR   −Y   OS ) 2 )}  (5)
 
     Calculation is running in the local coordinate system X OS =Y OS =0; thus, equation (5) is rewritten as:
 
 D   Curr =√{square root over (( X   TR   2   +Y   TR   2 )}  (6)
 
     The distance between ownship and traffic is written as a function of time. In the local coordinate system the position of ownship and traffic in time (t) is written as follows:
 
 X   OS     (t)     =X   OS   +v   OS   ·t ·cos γ OS   =v   OS   ·t ·cos γ OS  
 
 Y   OS     (t)     =Y   OS   +v   OS   ·t ·cos γ OS   =v   OS   ·t ·sin γ OS   (7)
 
 X   TR     (t)     =X   TR   +v   TR   ·t ·cos γ TR  
 
 Y   TR     (t)     =Y   TR   +v   TR   ·t ·sin γ TR   (8)
         Where:     OS =90−Ownship heading     TR =90−Traffic heading   (OS and TR represent the angle of ownship and traffic heading measured in local coordinate system).       

     Function of distance between the ownship and traffic is expressed as follows: 
     
       
         
           
             
               
                 
                   
                     D 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           ( 
                           
                             
                               X 
                               
                                 TR 
                                 
                                   ( 
                                   t 
                                   ) 
                                 
                               
                             
                             - 
                             
                               X 
                               
                                 OS 
                                 
                                   ( 
                                   t 
                                   ) 
                                 
                               
                             
                           
                           ) 
                         
                         2 
                       
                       + 
                       
                         
                           ( 
                           
                             
                               Y 
                               
                                 TR 
                                 
                                   ( 
                                   t 
                                   ) 
                                 
                               
                             
                             - 
                             
                               Y 
                               
                                 OS 
                                 
                                   ( 
                                   t 
                                   ) 
                                 
                               
                             
                           
                           ) 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
             
               
                 
                   
                     D 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           
                             
                               
                                 ( 
                                 
                                   
                                     X 
                                     TR 
                                   
                                   + 
                                   
                                     
                                       
                                         v 
                                         TR 
                                       
                                       · 
                                       t 
                                       · 
                                       cos 
                                     
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     
                                       γ 
                                       TR 
                                     
                                   
                                   - 
                                   
                                     
                                       
                                         v 
                                         OS 
                                       
                                       · 
                                       t 
                                       · 
                                       cos 
                                     
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     
                                       γ 
                                       OS 
                                     
                                   
                                 
                                 ) 
                               
                               2 
                             
                             + 
                           
                         
                       
                       
                         
                           
                             
                               ( 
                               
                                 
                                   Y 
                                   TR 
                                 
                                 + 
                                 
                                   
                                     
                                       v 
                                       TR 
                                     
                                     · 
                                     t 
                                     · 
                                     sin 
                                   
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     γ 
                                     TR 
                                   
                                 
                                 - 
                                 
                                   
                                     
                                       v 
                                       OS 
                                     
                                     · 
                                     t 
                                     · 
                                     sin 
                                   
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     γ 
                                     OS 
                                   
                                 
                               
                               ) 
                             
                             2 
                           
                         
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
           
         
       
     
     Development of the equation (9) results in following:
 
 D   (t) =√{square root over ( A·t   2   +B·t+C )}  (10)
         where:   A=v TR   2 −2·(v TR ·cos γ TR ·v OS ·cos γ OS +v TR ·sin γ TR ·v OS ·sin γ OS )+v OS   2      B=2·[X TR ·(v TR ·cos γ TR −v OS ·cos γ OS )−Y TR ·(v TR ·sin γ TR −v OS ·sin γ OS )]   C=X TR   2 +Y TR   2          

     Equation (10) indicates parabolic running of function D (t) . As an example,  FIG. 5  shows running of the function D (t)  in the interval t[−5, 30]. In this example, D (t)  is depicted under the following conditions:
         Ownship heading: 50°   Ownship speed: 30 knots   Traffic coordinates (foot): [755.6; −101.99]   Traffic heading: 340°   Traffic speed: 30 knots       

     From  FIG. 5  it is seen that, in a certain time, ownship and traffic will be at a minimum distance from each other (D (t)  reaches its minimum). Minimum of D (t)  shows in distance and time when ownship and traffic will pass each other if both airplanes maintain constant actual speed and heading. If the traffic is about to collide with ownship, the minimum of D (t)  will be less than “safe distance” (D Safe ). 
     If first derivative of function D (t)  is equal to zero, the time in which the distance between ownship and traffic will be minimum can be calculated. 
     To simplify the solution equation (10) is expressed as follows:
 
 D   (t)   2   =A·t   2   +B·t+C   (11)
 
     The first derivation of equation (11):
 
( D   (t)   2 )′=2 At+B ( D   (t)   2 )′=2 At+B   (12)
 
     The time of minimum of D (t)  is found if:
 
( D   (t)   2 )′=0           2 At   Min   +B= 0

     Hence 
     
       
         
           
             
               
                 
                   
                     t 
                     Min 
                   
                   = 
                   
                     - 
                     
                       B 
                       
                         2 
                         ⁢ 
                         A 
                       
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
     Substituting t Min  to the equation (10) the minimum value of D (t)  is obtained. The minimum value of D (t)  is the distance in which ownship and traffic pass each other (or “collide”).
 
 D   Min =√{square root over ( A·t   Min   2   +B·t   Min   +C )}  (14)
 
     If D Min  is less than D Safe , the traffic may represent a potential future threat. Then, the processor  24  calculates the distance in which traffic will pass ownship after ownship stops (D Stop ), if an alert is triggered at the current time. Calculation is done in the local coordinate system (X OS =Y OS =0). Using equation (3) the position of ownship in time is written as follows:
 
 X   OS STOP   =d   Brake ·cos(γ OS )
 
 Y   OS STOP   =d   Brake ·sin(γ OS )  (15)
 
     In the same time, under the assumption of constant speed and heading of traffic, the traffic is determined to be at the following position:
 
 X*   TR   =X   TR   +v   TR   ·T   STOP ·cos(γ TR )
 
 Y*   TR   =Y   TR   +v   TR   ·T   STOP ·sin(γ TR )  (16)
 
     For the condition above, the distance by which traffic is predicted to pass the ownship can be obtained from equation (9). For this case equation (10) is expressed as follows and distance by which traffic will pass the stationary ownship is calculated:
 
 D*   (t) =√{square root over (( X*   TR   +v   TR   ·t ·cos γ TR ) 2 +( Y*   TR   +v   TR   ·t ·sin γ TR ) 2 )}{square root over (( X*   TR   +v   TR   ·t ·cos γ TR ) 2 +( Y*   TR   +v   TR   ·t ·sin γ TR ) 2 )}
 
 D*   (t) =√{square root over ( A*·t   2   +B*·t+C* )}
 
 D*   (t)   2   =A*·t   2   +B*·t+C*   (17)
 
     Where:
         A*=v TR   2      B*=2·v TR ·(X* TR ·cos γ TR −Y* TR ·sin γ TR )   C*=X* TR   2 +Y* TR   2  
 
Hence:
       

     
       
         
           
             
               
                 
                   
                     t 
                     Min 
                     * 
                   
                   = 
                   
                     - 
                     
                       
                         B 
                         * 
                       
                       
                         2 
                         ⁢ 
                         
                           A 
                           * 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   18 
                   ) 
                 
               
             
             
               
                 
                   
                     D 
                     Stop 
                   
                   = 
                   
                     
                       
                         
                           A 
                           * 
                         
                         · 
                         
                           t 
                           Min 
                           
                             * 
                             2 
                           
                         
                       
                       + 
                       
                         
                           B 
                           * 
                         
                         · 
                         
                           t 
                           Min 
                           * 
                         
                       
                       + 
                       
                         C 
                         * 
                       
                     
                   
                 
               
               
                 
                   ( 
                   19 
                   ) 
                 
               
             
           
         
       
     
     D Stop  represents the expected distance by which traffic will pass the ownship if alert is triggered at present time and ownship is stopped under the assumption of equation (3). If the value of D Stop  is greater than the “safe distance” value (equation (4)), traffic is evaluated as “safe”. If the value of D Stop  is less than the “safe distance” value (equation (4)), traffic is evaluated as a threat and an alert is triggered. 
     In one embodiment, the processor  24  continuously evaluates the distance between ownship and traffic and the predicted separation distance D Stop  between ownship and traffic if ownship stops. If this distance is equal to or less than the safe distance, the alert is triggered. 
       FIG. 4  shows an example of two aircraft on crossing taxiways. 
     While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.