Abstract:
An aircraft traffic alert system that minimizes false alarms and unnecessary alerts by automatically adjusting the sensitivity of the system based on proximity to an airport. The system also can use information from a flight management system (FMS) or GPS navigation system (GNS) to only adjust the sensitivity near a destination airport and to suppress potential alerts for possible collisions with other aircraft that will be moot based on planned course changes of the subject aircraft. The system also can suppress alerts related to another aircraft when the other aircraft is landing on a parallel runway to the runway on which the subject aircraft is landing. The system may use multiple sensitivity levels based on different airspace classes, each class being associated with a different sensitivity level.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/490,898, filed on May 27, 2011. The entire teachings of the above application(s) are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Traffic alerting systems (e.g. Traffic Information Systems (TIS), Traffic Advisory Systems (TAS), Traffic Collision Avoidance Systems (TCAS), and Automatic Dependent Surveillance Broadcast (ADS-B) systems) are implemented in aircraft to monitor the location, speed, and heading of near-by aircraft and to alert a pilot to any aircraft that may present a threat of collision or other hazard. These systems all have a similar problem: the sensitivity needed enroute is different than that needed in the terminal environment.  FIG. 1  shows an aircraft  102  and the size (i.e., sensitivity) of the area covered by traffic alerting systems. The terminal sensitivity area  104  is smaller than the enroute sensitivity area  106 . Enroute, traffic alerting systems need to detect and alert conflicts at longer ranges due to the faster closing speeds encountered. There is also a lower density of traffic intruders in the enroute environment. This differs greatly from the terminal or airport environment where there is a higher density of traffic, which is slower moving. If the sensitivity that is optimal for the enroute environment is used in the terminal environment, there will be an increased number of false alarms, where a traffic intruder is alerted, but is not a threat. Additionally, if the sensitivity that is optimal for the terminal environment is used in the enroute environment, traffic alerts for intruders may be issued too late to prevent a collision or may require extreme maneuvering. 
     In previous systems, four methods have been used to adjust traffic alerting system&#39;s sensitivity. The first is manual control, where the pilot manually sets the sensitivity level. The second is based on pressure altitude. On departure, the pressure altitude increase is used to change from a terminal sensitivity to an enroute sensitivity. On approach, the pilot must manually set the destination airport elevation and as the plane descends towards the airport elevation, the sensitivity changes from enroute to terminal modes. This second method does not work well if an aircraft descends enroute but not near the destination airport. The third method involves the selection of a landing-related aircraft system, such as flaps or landing gear. When the landing system is deployed, indicating the pilot&#39;s intention to land, the traffic system changes sensitivity. This method does not work on aircraft with fixed landing gear or where the position of the landing gear or the flaps cannot be determined by the traffic system. The fourth method uses radio altitude to filter traffic on the ground, but only once a plane has descended below a certain altitude (often 2500 feet). 
     SUMMARY OF THE INVENTION 
     There is a market demand for an in-aircraft traffic alerting system that automatically adjusts its sensitivity based on the flying conditions and also that suppresses unnecessary alerts. Embodiments of the invention system determine a subject aircraft&#39;s present position, for example, using a GPS receiver, and comparing the determined position with a database of airport locations and respective predetermined airport airspace boundaries, and other airspaces, airways, etc. The traffic alert system automatically switches from a high sensitivity mode to a low (or lower) sensitivity mode when the determined position is within the predetermined airspace boundary of an airport of the database, or other airspaces, airways, etc. In other embodiments, the system only switches to the low (or lower) sensitivity mode if the aircraft is within the predetermined boundary of a destination airport. The system typically determines the destination airport from a flight plan an in-flight management system (FMS) or GPS navigation system (GNS). In other embodiments, alerts are suppressed. In other embodiments, the traffic alert system adjusts its sensitivity level to a level that corresponds with the class of airspace in which the aircraft is flying. 
     In other embodiments, the system suppresses alerts related to a possible collision with another aircraft if the subject aircraft&#39;s planned flight path will move it away from the collision with the second aircraft. In other embodiments, the system suppresses alerts related to another proximate aircraft if the other aircraft is on a final approach path to a runway that is parallel to a runway that the subject aircraft is on final approach to. 
     In other embodiments, the system receives information about the aircraft type of nearby aircraft and provides alert information based on flight characteristics of the type. For example, the system may provide a high risk warning over a large area for a Boeing 747-400 to account for collision risk and for risk associated with that aircraft type&#39;s large wake vortex. The system may also adjust the area around a nearby aircraft in which a warning is provided based on the maneuvering capabilities of the nearby aircraft type. The system also may look up in the database or have available (accessible) the maneuverability and flight characteristics of the aircraft in which it is installed, and use the information to alter alerting thresholds. 
     The system also may have intermediate sensitivity modes between the high sensitivity mode and the low sensitivity mode. The intermediate sensitivity mode may be one or more discrete sensitivity modes or may be a continuous sensitivity mode between the high sensitivity mode and the low sensitivity mode. The term continuous, as used herein, may mean infinite sensitivities between the high sensitivity mode and the low sensitivity mode, or may mean that increments between sensitivity levels are equal to or less than the capabilities of the system and/or the pilot to discern a change. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
         FIG. 1  illustrates a prior art traffic alert system having two sensitivity levels; 
         FIG. 2  illustrates an embodiment of a traffic alert system in which the sensitivity level is automatically changed when the aircraft enters a predetermined boundary of an airport; 
         FIG. 3  is a flow chart showing the process for automatically changing the sensitivity of the traffic alert system based on proximity to a predetermined airport airspace boundary; 
         FIG. 4  illustrates an embodiment of a traffic alert system where traffic alerts are suppressed for other aircraft landing on a parallel runway; 
         FIG. 5  illustrates an embodiment of a traffic alert system in which alerts are set based on the other aircraft&#39;s type and flight characteristics; 
         FIG. 6  illustrates an embodiment of a traffic alert system in which alerts are suppressed for other aircraft where a possible collision will be avoided by a planned course change in a flight plan; and 
         FIG. 7  is a block diagram of traffic alert system embodying the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A description of example embodiments of the invention follows. 
     A first embodiment combines a database with a surveillance system to provide improved services to the aircraft operator. The embodiment described here uses an airspace database and aircraft position and altitude to automatically set the sensitivity of the traffic system. The system utilizes an airspace database that contains latitudes, longitudes, and elevation of various airspaces and airways, e.g., an airspace above an airport. This database may be updated periodically. The system also uses a position and altitude source onboard the aircraft such as GPS to determine the aircraft&#39;s current position (latitude and longitude) and altitude. The system compares the current aircraft position and altitude with nearby airspace positions and altitudes as stored in the airspace database. As the aircraft travels within predetermined distances and altitudes from airspaces the traffic system automatically changes sensitivity levels. This happens automatically with no input (manual intervention) from the pilot. 
     The system also may have intermediate sensitivity modes between the high sensitivity mode and the low sensitivity mode. The intermediate sensitivity mode may be one or more discrete sensitivity modes or may be a continuous sensitivity mode between the high sensitivity mode and the low sensitivity mode. The term continuous, as used herein, may mean infinite sensitivities between the high sensitivity mode and the low sensitivity mode, or may mean that increments between sensitivity levels are equal to or less than the capabilities of the system and/or the pilot to discern a change. 
       FIG. 2  illustrates this first embodiment. An airport  202  is located on the ground  212 . The airport  202  is surrounded by a predetermined airport airspace boundary  204  that extends away (e.g., radially) from the airport along the ground and also extends vertically upwards to some predetermined altitude above the airport  202 . A first aircraft  206  is located at an altitude that is below the altitude of the predetermined airport airspace boundary  204 , but it is located outside of boundaries on the ground of the predetermined airport airspace boundary  204 . The first aircraft  206  has a system according to the first embodiment on board with a database that includes a record of the airport  202 , its location, and the predetermined airport airspace boundary  204 . The first aircraft  206  detects its position, e.g., using GPS, and determines that it is outside of the predetermined airport airspace boundary  204 . Therefore, the system sets its traffic alerting system to an enroute sensitivity mode. 
     The second aircraft  208  is located at an altitude below the altitude of the predetermined airport airspace boundary  204 , and also is located within the boundaries on the ground of the predetermined airport airspace boundary  204 . The second aircraft  208  also has a system according to the first embodiment on board. The second aircraft  208  detects its position and determines that it is inside of the predetermined airport airspace boundary  204 . Therefore, the system sets its traffic alerting system to a terminal sensitivity mode. 
     The third aircraft  210  is located within the boundaries on the ground of the predetermined airport airspace boundary  204 , but is located at an altitude above the predetermined airport airspace boundary  204 . The third aircraft  210  has a system according to the first embodiment on board. The third aircraft  210  detects its position and determines that it is outside of the predetermined airport airspace boundary  204 . Therefore, the system sets its traffic alerting system to an enroute sensitivity mode. 
       FIG. 3  is a flow chart for a system  100  according to the first embodiment described above. In a first step  302 , the system on board an aircraft determines its present three-dimensional position (longitude, latitude, and altitude). In step  304 , the system then compares the present three-dimensional position to a database of airspace locations (and predetermined airport boundaries) to determine whether the aircraft is within a predetermined airport airspace boundary. If the aircraft is not within a predetermined airport airspace boundary, then the aircraft&#39;s traffic alerting system is set to enroute sensitivity mode  306 . If the aircraft is within a predetermined airport airspace boundary, then the aircraft&#39;s traffic alerting system is set to terminal sensitivity mode  308 . As shown in  FIG. 3 , the steps shown repeat after a determination has been made and the sensitivity of the traffic alert system has been set. The system may repeat at any frequency, but it is preferable for the steps to repeat frequently to minimize the amount of time where the traffic alert system may be operating in the wrong sensitivity mode. As a non-limiting example, the sampling rate may be 1 to 2 Hertz. 
       FIG. 7  illustrates traffic alerting systems  100 ,  700  embodying the present invention. Common computer processors  780 , working memory (RAM, ROM, etc.), and I/O and network interfaces are employed with traffic alert assembly (routines, programs, algorithms, etc.) or device  713 . In the embodiment described above in FIGS.  2  and  3 , the database  710  containing the locations of airports and respective associated predetermined airport airspace boundary is contained in an on board database. In other embodiments, the database  710  may be located on a real-time accessible remote network database. In other embodiments, the traffic alert system  700  may include additional sensitivity levels between enroute and terminal sensitivity, including continuously variable sensitivity levels based on proximity to a subject airport. For example, the system  700  (its program assembly  713 ) could compare its determined position to flight space classifications, e.g., FAA Class A, Class B, etc. airspace, and set the sensitivity level based on the characteristics of the particular airspace it is in. In other embodiments, the system  700  (program assembly  713 ) also may use an aircraft&#39;s Flight Management System (FMS)  709  or GPS Navigation System (GNS)  705  to determine the aircraft&#39;s destination airport and only change the traffic alert device  713  from enroute sensitivity to terminal sensitivity when the system determines that the aircraft is within the predetermined airport airspace boundary of the destination airport. 
       FIG. 6  shows another embodiment of a traffic alert system  700  using an aircraft&#39;s FMS  709  or GNS  705 .  FIG. 6  shows a subject aircraft  602  on a collision course with a second aircraft  604 . If the subject aircraft  602  and the second aircraft  604  maintain their present courses, then they would collide at the possible collision point  610 . Normally, a traffic alert would be provided to prevent this collision. However, the subject aircraft  602  is following a flight plan that is programmed into the FMS or GNS. The flight plan includes a first flight leg  606  on which the subject aircraft  602  is currently flying and a second flight leg  608  onto which the subject aircraft  602  will be flying next. The subject aircraft  602  will be turning onto the second flight leg  608  before the subject aircraft  602  collides with the second aircraft  604 . The embodiment of the traffic alert system  700  (its device  713 ) receives the flight plan information from the FMS or GNS and suppresses the alert because the subject aircraft  602 , following the flight plan, will move away from the possible collision  610  with the second aircraft  604 . Additionally, the traffic alert system may have an input to determine if an autoflight system, like an autopilot, is currently engaged to follow the flight plan and, if so, presume that the subject aircraft will follow the flight plan. 
       FIG. 4  illustrates an additional embodiment that offers more sophisticated sensitivity adjustment within an airport&#39;s predetermined airport airspace boundary by including information about runways at airports and approach paths to the runways.  FIG. 4  shows two parallel runways  402   a,b  at an airport  412 . An aircraft  404  carrying a system  700  according to the additional embodiment is following the approach path  414  to land on runway  402   a . A second aircraft  406  is following the approach path  416  to land on runway  402   b . The system  700  onboard aircraft  404  detects aircraft  406 , but does not issue a traffic alert because the traffic alert assembly/device  713  determines that aircraft  406  likely is landing on parallel runway  402   b  and does not pose a collision risk. A third aircraft  408  is on the approach path  416  for runway  402   b , but the third aircraft  408  is not following the heading of approach path  416 . The traffic alert assembly/device  713  onboard aircraft  404  detects the third aircraft  408  and issues a traffic alert because it cannot determine that the third aircraft  408  is landing on the parallel runway  402   b , and therefore cannot rule out the possibility that the third aircraft  408  is on a collision course. Likewise, a fourth aircraft  410  is flying on a parallel course to the subject aircraft  404 , but the fourth aircraft is not on an approach path to any runway. Again, the traffic alert assembly/device  713  onboard aircraft  404  will issue a traffic alert for the fourth aircraft  410  because it cannot determine that the fourth aircraft  410  is landing on a parallel runway and therefore cannot rule out the possibility that the fourth aircraft  410  is a collision threat. 
     This invention thus reduces the false alarm rate of traffic alerting systems, while also increasing the detection rates of threat aircraft due to more accurate sensitivity levels. It also reduces pilot workload of having to manually change sensitivity levels or manually setting the destination airport elevation. 
       FIG. 5  shows another embodiment of the system  700  onboard a subject aircraft  502 . The aircraft  502  is flying along a flight path  512 . A second aircraft  504  is flying along a current flight path  520 . The flight paths of the two aircraft intersect. The second aircraft  504  broadcasts information  506  (received by the subject aircraft  502 ) that can be used to identify what type of aircraft the second aircraft  504  is. For example, the second aircraft may broadcast its tail number, which can be correlated against FAA data stored in database  710  to determine the aircraft&#39;s type. If the second aircraft&#39;s type is known, then information about the second aircraft&#39;s  504  performance can be determined by the invention system/assembly  713  onboard aircraft  502 . For example, the second aircraft&#39;s  504  turn capability can be determined (and also its climb performance capability) and in turn the outer bounds of the turn capability can be projected by traffic alert assembly/device  713 . For instance, a Boeing 747-400 flies at high speed, but cannot turn very quickly. By contrast, a helicopter flies slowly, but can change direction quickly. 
     Once the second aircraft&#39;s  504  turn capability is known, the area in which the second aircraft can be located in the near future can be determined by the invention assembly/system  713  on board the subject aircraft  502 . For example, the second aircraft  504  will most likely be on a flight path  508  close to its current flight path  520 . However, the second aircraft  504  may have a wider possible flight path  514  if the second aircraft  504  turns closer to its limits  510 . The embodiment of the traffic alert system can provide two types of alerts—a low risk alert  516  if the subject aircraft  502  will be in the possible flight path region  514 , and a high risk alert  518  if the subject aircraft  502  will be in the most-likely flight path region  508  of the second aircraft  504 . 
     The size of the high risk alert  518  region and that of the low risk alert region  516  also may be affected by other aspects of the second aircraft  504 . For example, a Boeing 747-400 has a large wake vortex that small aircraft must avoid flying through. Therefore, even though the 747-400 will be traveling relatively straight, its current flight path  520  may be wider than that of a smaller aircraft to account for the separation required to avoid the wake vortex. 
     The invention involves a periodically updated aircraft registration database  710  being incorporated into the traffic or wake-vortex separation system. The database  710  is configured to store registration numbers (e.g. N-numbers in the US) and aircraft models for a set of aircraft. It also stores a set of characteristics for each aircraft model. If a detected aircraft&#39;s registration number (as detected by Mode-S ID or ADS-B) is in the database, the characteristics of the model are determined then used for the traffic avoidance algorithms or wake-vortex algorithms, as described above. Likewise, if a detected aircraft&#39;s aircraft model is received by the traffic system, then the characteristics of the model are determined and used for traffic avoidance or wake-vortex algorithms. 
     This system increases the performance of the traffic or wake-vortex avoidance system by reducing the false alarm rate and increasing the probability of correctly identifying a threat aircraft. 
     The teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety. 
     While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.