Abstract:
Systems and methods for identifying ownship deviation from assigned taxi-clearance in the area of taxiway intersection. An exemplary system provides alerts in the event of a significant deviation from the assigned clearance, but does not give unwanted alerts when the flight crew is performing normal turning maneuvers in the area of an intersection.

Description:
BACKGROUND OF THE INVENTION 
     One of the projects of the Single European Sky Air Traffic Management Research is to improve the crew awareness when the ownship (which may be an aircraft or a ground vehicle) deviates from a taxi-clearance assigned by air traffic control (ATC). 
     Any system providing a solution will have a problem addressing when a vehicle deviates from the taxi clearance in an intersection area. Especially in the case of a small angle between intersecting taxiways (causing a big turn), the real trajectory and maintained turn radius of ownship fully depend on the flight crew and are “unpredictable” for any system onboard the ownship. Monitoring change of ownship heading and position during the turn is not feasible, due to the fact that the ownship can start the turn by turning to the opposite direction, see  FIG. 1-1 . How much ownship turns and goes to the opposite direction before it starts turning on the assigned taxiway fully depends on the technique used by the flight crew. 
       FIG. 1-2  is an aerial photograph of an airport taxiway intersection showing various tire marks in several locations, and presents evidence that different airplanes make the same turn with different radii (trajectory). The challenge is to provide an alert, if the crew makes a significant deviation from the assigned clearance, while permitting normal maneuvering without providing unwanted alerts. 
     SUMMARY OF THE INVENTION 
     The invention solves the problem of identification of ownship deviation from assigned taxi-clearance in the area of taxiway intersection. The presented solution provides alerts in the event of a significant deviation from the assigned clearance, but does not give unwanted alerts when the flight crew is performing normal turning maneuvers in the area of an intersection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings: 
         FIGS. 1-1  and  1 - 2  are overhead views of taxiway intersections that experience various radius turns by aircraft making transitions from one taxiway to the other taxiway; 
         FIG. 2  is a block diagram of an exemplary system formed in accordance with an embodiment of the present invention; 
         FIGS. 3 ,  4 ,  7 , and  10  are flowcharts of exemplary processes performed by the system shown in  FIG. 2 ; and 
         FIGS. 5 ,  6 ,  8 ,  9 ,  11 , and  12  illustrate geographical representations of one of the processes shown in  FIG. 3 ,  4 ,  7 , or  10 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  shows a system  20  located on a vehicle (i.e., ownship), such as an aircraft or airport ground vehicle, for alerting if the crew of the vehicle makes a significant deviation from an assigned taxiway clearance, while permitting normal maneuvering without providing unwanted alerts. The system  20  includes a processor  24  that is in signal communication with a user interface device  26 , a data communication device  28 , a database  30 , an output device  32 , and a positioning system  34 . The processor  24  receives vehicle position information from the positioning system  34 , airport taxiway and vehicle information from the database(s)  30 , and taxiway clearance information from the user interface device  26  or from a remote source via the data communication device  28 . Based on the received data, the processor  24  determines if the vehicle has deviated from the taxiway clearance, except within a control area or inhibit zone associated with taxiway intersections. 
     An inhibit area (zone) is defined by the taxiway on which the ownship is currently taxiing as it approaches a taxiway intersection and by the taxiway on which ownship is cleared to exit the taxiway intersection. The processor  24  calculates the angle between the assigned taxiways and the size of the inhibit zone according to magnitude of the angle, the width of the taxiways (not in all embodiments), and the known dimensions of ownship. The inhibit zone is defined to be compatible with commonly used taxiway centerline radius dimensions as defined in Federal Aviation Administration (FAA) Advisory Circular AC 150/5300-13. The inhibit zone is a circle or a polygon, but other shapes are possible. 
     Once the ownship enters the inhibit zone, the processor  24  inhibits taxiway clearance alerting until the ownship exits the zone. If the ownship is not on the assigned taxiway and aligned with the assigned taxiway, the alert is triggered when the ownship is not within any inhibit zone. If the ownship is within the bounds of the correct taxiway, no alert is given. 
     In one embodiment, the alerts provided by the processor  24  include graphically highlighted areas of a cockpit map display (the output device  32 ), text messages on the display, or aural messages provided to the crew via cockpit loudspeaker or headset (the output device  32 ). 
       FIG. 3  illustrates an exemplary process  50  performed by the system  20  shown in  FIG. 2  for detecting ownship deviation from an assigned taxiway clearance, except for within a defined inhibit zone located at taxiway intersections within the taxiway clearance. First, at a block  54 , taxiway clearance is received from a ground taxi authority, e.g., ATC. Next at a block  56 , the processor  24  calculates all inhibit zones based on the taxiway clearance and airport geometry information retrieved from the database  30 . In one embodiment, inhibit zone information is precalculated by the ownship or a control authority for all taxiway intersections and directions of travel. The precalculated inhibit zone information is stored in in short-time memory of the processor  24  or the database  30 . If the inhibit zone information is generated by the control authority, the ownship receives it from the control authority via the data communication device  28  (e.g., Controller Pilot Data Link Communications (CPDLC)). In this embodiment, the processor retrieves the precalculated inhibit zone information associated with the taxiway clearance. 
     Then, at a block  60 , the processor  24  receives aircraft location information from the positioning system  34 . Then, at a decision block  62 , the processor  24  determines if the aircraft is within a calculated inhibit zone. If the aircraft is determined to not be within one of the calculated inhibit zones, then, at a block  64 , the processor  24  outputs an alert to the output device  32 , if the aircraft is not currently adhering to the taxiway clearance. If the aircraft was determined to be within an inhibit zone, then, at a block  66 , the analysis of whether the aircraft is adhering to the taxiway clearance is inhibited. Then, at a decision block  70 , processor  24  determines if the aircraft has departed the inhibit zone. Once the aircraft has departed the inhibit zone, then the process  50  proceeds to the block  64 . 
       FIG. 4  illustrates an exemplary process  56 - 1  for performing the calculation of inhibit zones performed at block  56  in  FIG. 3 . First, at block  80 , a first taxiway interchange in the taxiway clearance is found. Next, at a block  82 , width, centerline location, and heading information are retrieved from the runway database  30  for the two taxiways associated with the found taxiway interchange. At a block  84 , the intersection point of the centerlines of the two taxiways and the angle between the two taxiways are calculated based on the retrieved information. Next at a block  86 , the centerpoint and the radius of the inhibit zone are calculated, based on the taxiway width and a factor that is a function of the angle between the two taxiways. Next, at a decision block  88 , the process  56 - 1  determines if all of the taxiway intersections on the taxiway clearance have been analyzed. If not all of the taxiway interchanges have been analyzed, then at a block  90 , the process  56 - 1  repeats for the next taxiway intersection in the taxiway clearance. Otherwise, the process  56 - 1  returns and proceeds to block  60 , as shown in  FIG. 3 . 
       FIG. 5  illustrates an inhibit zone  92  generated for two taxiways that form an acute angle on a taxiway clearance. The inhibit zone  92  is that generated from the process shown in  FIG. 4 . 
       FIG. 6  illustrates an inhibit zone  94  between two taxiways that form an obtuse angle between the two. The inhibit zones  92  and  94  are defined by the radius and the centerpoint of the inhibit zone. The centerpoint of the inhibit zone is defined by an offset value d that is defined based on the radius and a factor that is a function of the included angle between the taxiways. 
     The calculations required to obtain radius R and offset distance D Offset  for the circular inhibit zones  92 ,  94  shown in  FIGS. 5 and 6  are as follows. First, the included angle θ between the taxiway centerlines is calculated. Then the radius of the circle is calculated from eq. 1.
 
 R= 2· TWY   Width   ·K   R   (1)
 
     where factor K R  is a function of the included angle θ. 
     Offset distance D offset  is given by eq. 2. 
     
       
         
           
             
               
                 
                   
                     D 
                     Offset 
                   
                   = 
                   
                     
                       R 
                       · 
                       
                         K 
                         C 
                         2 
                       
                     
                     2 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     where factor K c  is a function of the included angle θ. 
       FIG. 7  illustrates another exemplary process  56 - 2  for calculating the inhibit zones, as shown in block  56  of  FIG. 3 . The first three steps  80 - 1 ,  82 - 1 , and  84 - 1  are similar to steps  80 - 84  shown in  FIG. 4  except width is not used. Then, at a block  100 , centerline radius of turn is calculated based on the included angle θ between the two taxiway centerlines, a predefined minimum recommended turn radius, a predefined minimum angle value, and a predefined parabolic function factor. Next, at a block  102 , lines that are tangent to a circle having the calculated centerline radius of turn and that correlate to the centerlines for the two runways are determined. The tangent points of those determined lines is determined. 
     Next, at a block  104 , the radius of an inhibit zone (circle) is calculated based on the tangent points. Next, at a block  106 , an offset of the inhibit circle is calculated based on the intersection point and the tangent points. At a block  110 , location of the center of the inhibit circle is calculated based on the offset and the angle between the taxiways. Blocks  88 - 1  and  90 - 1  are similar to blocks  88  and  90  from  FIG. 4  and provide the function of repeating for all of the taxiway interchanges within the current analyzed taxiway clearance. 
       FIGS. 8 and 9  illustrate inhibit zones  112 ,  114  for taxiways that have an included angle θ that is acute and an included angle θ that is obtuse, respectively. 
     The following are exemplary algorithms used by the processor  56 - 2  shown in  FIG. 7 . The centerline radius of turn is calculated as a function of the included angle θ. 
     
       
         
           
             
               
                 
                   
                     
                       R 
                       T 
                     
                     = 
                     
                       
                         R 
                         0 
                       
                       + 
                       
                         
                           
                             ( 
                             
                               Θ 
                               - 
                               
                                 Θ 
                                 0 
                               
                             
                             ) 
                           
                           2 
                         
                         
                           2 
                           · 
                           p 
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   where 
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     p 
                     = 
                     
                       
                         const 
                         . 
                         
                           
 
                         
                         ⁢ 
                         
                           Θ 
                           0 
                         
                       
                       = 
                       
                         
                           const 
                           . 
                           
                             
 
                           
                           ⁢ 
                           
                             R 
                             0 
                           
                         
                         = 
                         
                           const 
                           . 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     FAA AC 150/5300-13 defines recommendations for airport design. Based on this FAA document and review of some international airports&#39; layouts, the values of minimum angle and centerline radius between two intersecting taxiways has been defined. These defined values are used as a constants in the presented calculation (R 0 —Minimum centerline radius; θ 0 —Minimum angle between two taxiways). 
     The centerline radius changes with the change of angle between two taxiways. In one embodiment, the change of centerline radius is approximated by a parabolic function (see equation 3; parameter [p] is parabolic function factor used for approximation of centerline radius change). 
     The tangent points A[X,Y] and B[X,Y] of radius R T  and both taxiways are calculated. 
     
       
         
           
             
               
                 
                   
                     
                       D 
                       T 
                     
                     = 
                     
                       
                         
                           R 
                           T 
                         
                         
                           tg 
                           ⁡ 
                           
                             ( 
                             
                               Θ 
                               2 
                             
                             ) 
                           
                         
                       
                       ⇒ 
                       
                         A 
                         ⁡ 
                         
                           [ 
                           
                             X 
                             , 
                             Y 
                           
                           ] 
                         
                       
                     
                   
                   ; 
                   
                     B 
                     ⁡ 
                     
                       [ 
                       
                         X 
                         , 
                         Y 
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     For the included angle θ between the taxiway centerlines greater than 90° the circle area can be located in the point of intersection of included angle centerline and connection line of tangent points A[X,Y] and B[X,Y]. 
     
       
         
           
             
               
                 
                   
                     
                       X 
                       E 
                     
                     = 
                     
                       
                         X 
                         
                           
                             
                               Center 
                               ⁢ 
                               _ 
                             
                             ⁢ 
                             90 
                           
                           → 
                           180 
                         
                       
                       = 
                       
                         
                           X 
                           A 
                         
                         + 
                         
                           
                             
                               X 
                               B 
                             
                             - 
                             
                               X 
                               A 
                             
                           
                           2 
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       Y 
                       E 
                     
                     = 
                     
                       
                         Y 
                         
                           
                             
                               Center 
                               ⁢ 
                               _ 
                             
                             ⁢ 
                             90 
                           
                           → 
                           180 
                         
                       
                       = 
                       
                         
                           Y 
                           B 
                         
                         + 
                         
                           
                             
                               Y 
                               A 
                             
                             - 
                             
                               Y 
                               B 
                             
                           
                           2 
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     R 
                     = 
                     
                       
                         
                           
                             ( 
                             
                               
                                 X 
                                 A 
                               
                               - 
                               
                                 X 
                                 
                                   
                                     
                                       Center 
                                       ⁢ 
                                       _ 
                                     
                                     ⁢ 
                                     90 
                                   
                                   → 
                                   180 
                                 
                               
                             
                             ) 
                           
                           2 
                         
                         + 
                         
                           
                             ( 
                             
                               
                                 Y 
                                 A 
                               
                               - 
                               
                                 Y 
                                 
                                   
                                     
                                       Center 
                                       ⁢ 
                                       _ 
                                     
                                     ⁢ 
                                     90 
                                   
                                   → 
                                   180 
                                 
                               
                             
                             ) 
                           
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     For the included angle θ between the taxiway centerlines smaller than 90° definition of circle area center is based on the dimension D Offset  definition. 
     
       
         
           
             
               
                 
                   
                     D 
                     Offset 
                   
                   = 
                   
                     
                       K 
                       D 
                     
                     · 
                     
                       
                         
                           
                             
                               ( 
                               
                                 
                                   X 
                                   E 
                                 
                                 - 
                                 
                                   X 
                                   P 
                                 
                               
                               ) 
                             
                             2 
                           
                           + 
                           
                             
                               ( 
                               
                                 
                                   Y 
                                   E 
                                 
                                 - 
                                 
                                   Y 
                                   P 
                                 
                               
                               ) 
                             
                             2 
                           
                         
                       
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     where K D =const. 
     Position of center of circle area is given by eqs. 7. 
     
       
         
           
             
               
                 
                   
                     
                       X 
                       
                         
                           
                             Center 
                             ⁢ 
                             _ 
                           
                           ⁢ 
                           0 
                         
                         → 
                         90 
                       
                     
                     = 
                     
                       
                         X 
                         P 
                       
                       - 
                       
                         
                           D 
                           Offset 
                         
                         · 
                         
                           cos 
                           ⁡ 
                           
                             ( 
                             
                               Θ 
                               2 
                             
                             ) 
                           
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       Y 
                       
                         
                           
                             Center 
                             ⁢ 
                             _ 
                           
                           ⁢ 
                           0 
                         
                         → 
                         90 
                       
                     
                     = 
                     
                       
                         Y 
                         P 
                       
                       - 
                       
                         
                           D 
                           Offset 
                         
                         · 
                         
                           sin 
                           ⁡ 
                           
                             ( 
                             
                               Θ 
                               2 
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     Radius of circle area is defined by the following. 
     
       
         
           
             
               
                 
                   R 
                   = 
                   
                     
                       K 
                       R 
                     
                     · 
                     
                       
                         
                           
                             ( 
                             
                               
                                 X 
                                 A 
                               
                               - 
                               
                                 X 
                                 
                                   
                                     
                                       Center 
                                       ⁢ 
                                       _ 
                                     
                                     ⁢ 
                                     0 
                                   
                                   → 
                                   90 
                                 
                               
                             
                             ) 
                           
                           2 
                         
                         + 
                         
                           
                             ( 
                             
                               
                                 Y 
                                 A 
                               
                               - 
                               
                                 Y 
                                 
                                   
                                     
                                       Center 
                                       ⁢ 
                                       _ 
                                     
                                     ⁢ 
                                     0 
                                   
                                   → 
                                   90 
                                 
                               
                             
                             ) 
                           
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     where factor K R  is a function of the included angle. 
       FIG. 10  illustrates an exemplary process  56 - 3  for generating inhibit zones that are polygons, from block  56  of  FIG. 3 . The first three steps, blocks  80 - 2 ,  82 - 2 , and  84 - 2  of the process  56 - 3 , are similar to steps  80 - 84 , as shown in  FIG. 4 . The next two steps (blocks  100 - 1 ,  102 - 1 ) are identical to those at blocks  100  and  102  of  FIG. 7 . Next, at a block  120 , dimensions of the polygon are calculated based on width of the taxiways, the tangent points, the angle between the taxiways, and the two calculated offset values. The process  56 - 3  repeats in a similar manner to that of  FIGS. 4 and 7  (blocks  88 ,  88 - 1 ,  90 ,  90 - 1 ) until all of the taxiway interchanges have been analyzed. 
       FIG. 11  illustrates a polygon inhibit zone  140  formed in accordance with the process  56 - 3  shown in  FIG. 10 . 
     Taxiway centerline turn radius R T , tangent points A[X,Y] and B[X,Y], and dimension D T  defined above are used. 
     In one embodiment, dimensions P D  and P B  are calculated as follows: 
     
       
         
           
             
               
                 
                   
                     
                       P 
                       D 
                     
                     = 
                     
                       
                         
                           ( 
                           
                             
                               D 
                               T 
                             
                             + 
                             
                               D 
                               L 
                             
                           
                           ) 
                         
                         · 
                         
                           cos 
                           ⁡ 
                           
                             ( 
                             
                               Θ 
                               2 
                             
                             ) 
                           
                         
                       
                       + 
                       
                         
                           ( 
                           
                             
                               D 
                               Y 
                             
                             + 
                             
                               
                                 TWY 
                                 Width 
                               
                               2 
                             
                           
                           ) 
                         
                         · 
                         
                           sin 
                           ⁡ 
                           
                             ( 
                             
                               Θ 
                               2 
                             
                             ) 
                           
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       P 
                       B 
                     
                     = 
                     
                       
                         P 
                         D 
                       
                       - 
                       
                         
                           ( 
                           
                             
                               D 
                               Y 
                             
                             + 
                             
                               
                                 TWY 
                                 Width 
                               
                               2 
                             
                           
                           ) 
                         
                         · 
                         
                           
                             cos 
                             ⁡ 
                             
                               ( 
                               
                                 2 
                                 ⁢ 
                                 Θ 
                               
                               ) 
                             
                           
                           
                             sin 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             Θ 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     where dimensions D L  and D Y  are a constant. 
       FIGS. 12-1  through  12 - 5  illustrate various other taxiway interchanges and resulting circular and polygonal inhibit zones. 
     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.