Abstract:
Systems and methods for alerting to traffic proximity in the airport environment. Knowledge of the geographic position, speed, rate of change of speed, heading (or track-angle) and/or altitude of own-aircraft (or vehicle) and another, potentially conflicting aircraft (or vehicle) are used to calculate a predicted distance between the two aircraft (or vehicles) at given point of time in the future. If separation distance is predicted to be less than a predetermined acceptable value, then an alert message (aural, visual or both) is issued to the pilot or operator of the vehicle.

Description:
GOVERNMENT INTEREST 
     The invention described herein was made in the performance of work under FAA Agreement #DTFAWA-09-00001. The Government may have rights to portions of this invention. 
    
    
     BACKGROUND OF THE INVENTION 
     Several collision accidents have occurred at airports where an aircraft or vehicle has entered a runway environment which is already occupied by another aircraft that is moving at significant speed. Airborne collision protection and mitigation is provided by Traffic Collision and Avoidance System (TCAS), however the algorithms used in TCAS systems are not well suited to the airport surface operations problem; on airports, near runways, aircraft commonly operate at relatively high speeds in close proximity to other aircraft and vehicles. For example, an aircraft waiting to enter a runway is commonly stopped within a distance of the order of 100 feet from a runway that may be occupied by a landing aircraft traveling at speeds greater than 100 knots, thereby confusing TCAS algorithms. Also, on the ground at normal taxi speeds, an airplane can change its direction of travel much more rapidly than can an airborne aircraft. 
     SUMMARY OF THE INVENTION 
     The present invention uses knowledge of the geographic position, speed, rate of change of speed, heading (or track-angle) and/or altitude of own-aircraft (or vehicle) and another, potentially conflicting aircraft (or vehicle) to calculate the predicted distance between the two aircraft (or vehicles) at given point of time in the future. If separation distance is predicted to be less than a predetermined acceptable value, then an alert message (aural, visual or both) is issued to the pilot or operator of the vehicle. The required information from the potentially conflicting traffic is obtained over a data communication channel, such as Automatic Dependent Surveillance-Broadcast (ADS-B), Automatic Dependent Surveillance-Rebroadcast (ADS-R) or Traffic Information Service-Broadcast (TISB) data. The information required from own-aircraft is readily available from on-board systems such as Global Positioning Systems and Air Data Systems. 
    
    
     
       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  illustrates a schematic diagram of an example system for performing traffic proximity alerting in the airport environment in accordance with an embodiment of the present invention; 
         FIG. 2  illustrates a flow diagram for performing traffic proximity alerting in the airport environment using the system shown in  FIG. 1 ; 
         FIG. 3  illustrates runway proximity zone used by the present invention; 
         FIG. 4  is a flow diagram of an example process for testing alerting status of traffic; 
         FIGS. 5A  and B a flowchart of an example process used to calculate the predicted separation distance between ownship and the target at a future time; 
         FIG. 6  illustrates caution and warning target icons presented on a display of a host vehicle; and 
         FIGS. 7 and 8  illustrate plan views of an airport area displaying caution and warnings in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an example vehicle collision alerting system  20  for providing warning and/or caution alerts to vehicle operators if ground based trajectories of own and other vehicles might lead to a collision. The system  20  includes a processor  24 , an air data system (ADS)  26 , a position determining device (e.g. global positioning system (GPS)  30 ), a transponder  32  and one or more output device  34 . 
     The processor  24  sends and receives state information over a data channel via the transponder  32 . Using own-vehicle information (from the GPS  30  and the ADS  26 ) and target vehicle state information (position, velocity, acceleration and track-angle), the processor  24  calculates predicted range between the two vehicles for a set of future times. If the predicted range is less than a pre-determined “allowable miss distance” at a time less than Tw, then a Warning alert is generated and outputted to one of the output device(s)  34 . If the predicted range is less than the “allowable miss distance” at a time less than Tc, then a Caution alert is generated and outputted to one of the output device(s)  34 . 
     The processor  24  provides predictions for many scenarios—i.e. for converging runway traffic as well as same runway traffic. However, to avoid missed alerts when either own-vehicle or the target vehicle is changing track-angle rapidly—which happens on the ground—the predicted positions are calculated at a set of future times—e.g. every three seconds out to 30 seconds, i.e. 10 calculations. This frequency can vary. Also, the accelerations (rate of change of speed) of own-vehicle and target vehicle are used to provide more accurate predictions. Acceleration of the target vehicle is calculated from reported velocity (or geographic position), and filtered to reduce noise. 
     In another embodiment, the processor  24  uses track-angle data from own-vehicle and traffic vehicle to calculate track-angle rate to improve the prediction of position when own-vehicle and/or target vehicle is turning. Since the relative positions of the own-vehicle and the traffic vehicle are known, the direction from which the target vehicle is converging is also calculated, and the direction can be included in the alert message: e.g. “Traffic left”, or “Traffic 9 o&#39;clock”. 
       FIG. 2  illustrates an example process  50  performed by the system  20  shown in  FIG. 1 . When a vehicle (e.g. aircraft, ground crew vehicle) is on the ground, a ground signal is transmitted over a data communication channel, see block  54 . Next at block  56 , for all vehicles receiving the ground signal transmission that are less than threshold altitude above an associated runway altitude value, locations at a set of times in the future of the vehicle receiving the ground signal transmission and vehicle transmitting the ground signal are predicted. Then at block  58 , distance between the locations at corresponding times are determined. 
     At a decision block  62 , the processor  24  determines if one of the determined distances between corresponding times is below a predefined threshold. If one of the determined distances is below the threshold, then at decision block  64 , the processor  24  determines if the time corresponding to the determined distance is below a first time threshold. If the corresponding time is below the first time threshold, the system  20  outputs a warning alert, see block  66 . If none of the determined distances are below the predefined threshold, the process  50  is delayed at block  63  and returned to block  56 . 
     If the corresponding time is not below the first time threshold, then at decision block  70 , the processor  24  determines if the time corresponding to the determined distance is between the first time threshold and a second time threshold. If the corresponding time is not between the first and second time threshold, the process  50  is delayed at block  72  then returned to decision block  64 . If the corresponding time is between the first and second time threshold, the system  20  outputs a caution alert at block  74 . 
       FIG. 3  illustrates an example of runway proximity zone, which defines the volume of interest around a runway. A primary condition for triggering an alert is that both “ownship” and a traffic target must be in the proximity zone. In one embodiment, the width of the zone increases if the velocity component of ownship or target towards the runway is above a predefined value(s). 
       FIG. 4  is a flowchart of an example process  80  for testing alert status of a traffic target. If the target aircraft/vehicle is within the proximity zone, T A  is made equal to the time interval between calculations (dT—e.g., 1 second). T A  varies between dT and TCaution in steps of dT. If T A  is less than or equal to TCaution, then range of target from ownship is predicted at T A  seconds. In one embodiment, TCaution is ˜30 seconds and TWarn is ˜15 seconds. If the predicted range is greater than a predefined clearance distance, the process  80  increments T A  by dT and repeats the analysis. If the predicted range is less than the predefined clearance distance, the process  80  outputs a warning alert if T A  is greater than a predefined TWarn, otherwise caution alert is outputted. A warning alert may include a visual symbol (e.g., red icon) or an aural message (e.g., “Traffic Ahead”). A tactile alert may also be outputted. 
     If T A  is not less than or equal to TCaution or the target is not inside the proximity zone, then the process  80  proceeds to analyze the next target aircraft/vehicle based on observed ADS-B traffic targets. 
       FIGS. 5A  and B illustrate a flowchart of an example process  90  used to calculate the predicted separation distance between ownship and the target at a future time. T P  is the same as T A . The average accelerations (rate of change of forward velocity) of ownship and traffic targets are calculated using the following algorithm. The algorithm averages the acceleration value over N samples, where N is typically of the order of 10. 
     
       
         
           
             
               AvgAccel 
               K 
             
             = 
             
               
                 ∑ 
                 
                   i 
                   = 
                   0 
                 
                 
                   N 
                   - 
                   1 
                 
               
               ⁢ 
               
                   
               
               ⁢ 
               
                 
                   ( 
                   
                     
                       V 
                       
                         K 
                         - 
                         i 
                       
                     
                     - 
                     
                       V 
                       
                         k 
                         - 
                         i 
                         - 
                         1 
                       
                     
                   
                   ) 
                 
                 / 
                 dT 
               
             
           
         
       
     
     Where AvgAccel K  is the average acceleration in the K th  time interval, N is the number of averaging samples, V K-i  is the velocity at the i th  sample before the current time interval, V K-i-1  is the velocity at the (i-1) th  sample before the current time interval, and dT is the time step used in the calculations (typically 1 second). 
       FIG. 6  illustrate icons  140  and  142  that are presented on an own aircraft display in plan view for representing any target aircraft/vehicles. The first icon  140  includes a triangular vehicle symbol inside a circular perimeter that is presented when a vehicle associated with the first icon  140  has triggered a caution alert. In one embodiment, the first icon  140  is presented as a distinct color (e.g., yellow). The second icon  142  includes a triangular vehicle symbol inside a square perimeter that is presented when a vehicle associated with the second icon  142  has triggered a warning alert. In one embodiment, the second icon  142  is presented as a distinct color (e.g., red). Relevant and proximate traffic would be displayed without the encompassing circle/square and would not be displayed in the distinct color—yellow or red. 
       FIG. 7  illustrates a plan view radar display with the own aircraft  150  center in circular range circles. In this situation, the alerting system on the own aircraft  150  has received a ground signal from a target aircraft associated with the aircraft icon  154  and determined that the target meets the criteria of a caution alert. Thus, the aircraft icon  154  appears similar to icon  140  as shown in  FIG. 6 . Also, a line  158  that extends along the direction of travel from the icon  154  is presented on the display. The line  158  is determined based on status information received from the target aircraft. The line  158  is presented in the same color as the icon  154 . 
       FIG. 8  illustrates a situation where the alerting system on the own aircraft  150  has received a ground signal from a target aircraft associated with an aircraft icon  154 - 1  and determined that the target meets the criteria of a warning alert. Thus, the aircraft icon  154 - 1  appears similar to icon  142  as shown in  FIG. 6 . Also, a line  160  that extends along the direction of travel from the icon  154 - 1  is presented on the display. The line  150  is determined based on status information received from the target aircraft as described above. The line  150  is presented in the same color as the icon  154 - 1 . 
     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.