Patent Publication Number: US-9898934-B2

Title: Prediction of vehicle maneuvers

Description:
TECHNICAL FIELD 
     This disclosure relates to collision prevention in aviation. 
     BACKGROUND 
     Air traffic control systems track positions and velocity of aircraft and help manage aircraft trajectories. Air traffic control may be based on radar surveillance, supplemented more recently with cooperative radio surveillance techniques, such as automatic dependent surveillance-broadcast (ADS-B). An aircraft may determine its own position, such as via a Global Navigation Satellite System (GNSS), and periodically broadcast its position via a radio frequency, which may be read by ground stations and other aircraft. Aircraft position data may be provided to a variety of other applications that serve functions such as traffic situational awareness, traffic alert, and collision avoidance, for example. 
     SUMMARY 
     This disclosure is directed to systems, devices, and methods for generating air traffic alerts. A system of this disclosure may predict a future vehicle maneuver based at least in part on the location and course of a vehicle. The predicted future vehicle maneuver may be a turn or a change in altitude. The system may also use a set of protocol data for standard procedures, such as national or international aviation regulations, to predict the future vehicle maneuver. The system may use the predicted future vehicle maneuver to modify a baseline protection volume for the vehicle. For example, the modified protection volume may extend in the direction of a predicted turn or change in altitude. 
     In one example, a system is configured to receive surveillance data from a vehicle, determine a location of the vehicle based at least in part on the received surveillance data, and determine a course of the vehicle based at least in part on the received surveillance data. The system is further configured to predict a future vehicle maneuver for the vehicle based at least in part on the location and the course of the vehicle, and based at least in part on a set of protocol data indicating one or more standard procedures for one or more vehicle maneuvers. The system is further configured to determine, based at least in part on the predicted future vehicle maneuver, a modified protection volume for the vehicle that is modified relative to a baseline protection volume for the vehicle. The system is further configured to generate an output based on the modified protection volume. 
     In another example, a method includes receiving surveillance data from a vehicle, determining a location of the vehicle based at least in part on the received surveillance data, and determining a course of the vehicle based at least in part on the received surveillance data. The method further includes predicting a future vehicle maneuver for the vehicle based at least in part on the location and the course of the vehicle, and based at least in part on a set of protocol data indicating one or more standard procedures for one or more vehicle maneuvers. The method further includes determining, based at least in part on the predicted future vehicle maneuver, a modified protection volume for the vehicle that is modified relative to a baseline protection volume for the vehicle and generating an output based on the modified protection volume. 
     Another example is directed to a system comprising means for receiving surveillance data from a vehicle. The system further comprises means for determining a location of the vehicle based at least in part on the received surveillance data and means for determining a course of the vehicle based at least in part on the received surveillance data. The system further comprises means for predicting a future vehicle maneuver for the vehicle based at least in part on the location and the course of the vehicle, and based at least in part on a set of protocol data indicating one or more standard procedures for one or more vehicle maneuvers. The system further comprises means for determining, based at least in part on the predicted future vehicle maneuver, a modified protection volume for the vehicle that is modified relative to a baseline protection volume for the vehicle and means for generating an output based on the modified protection volume. 
     The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  depicts a conceptual block diagram of an example air traffic data system that includes a Traffic Collision Avoidance System (TCAS) computer. 
         FIG. 2  depicts an example functional block diagram of an example TSAA system with additional detail in accordance with illustrative examples in which a conflict detector unit includes an aircraft maneuver prediction unit, as shown in  FIG. 1 . 
         FIG. 3  depicts an example takeoff maneuver for an aircraft, in accordance with some examples of this disclosure. 
         FIG. 4  depicts a graph of vertical velocity, horizontal velocity, and altitude for an aircraft during takeoff, in accordance with some examples of this disclosure. 
         FIG. 5  depicts trajectory propagation for an aircraft using constant velocity, in accordance with some examples of this disclosure. 
         FIG. 6  depicts trajectory propagation for an aircraft using an intention-based predictive algorithm, in accordance with some examples of this disclosure. 
         FIG. 7  depicts trajectory propagation for an aircraft using a threshold velocity to reduce acceleration, in accordance with some examples of this disclosure. 
         FIG. 8  depicts a two-dimensional side view of a modified protection volume based at least in part on a predicted future aircraft maneuver, in accordance with some examples of this disclosure. 
         FIG. 9  depicts a two-dimensional side view of a baseline protection volume after a predicted future aircraft maneuver has started, in accordance with some examples of this disclosure. 
         FIG. 10  shows a conceptual perspective diagram of an airfield traffic pattern for a runway, in accordance with some examples of this disclosure. 
         FIG. 11  shows a two-dimensional top view of a modified protection volume based at least in part on a predicted aircraft maneuver near an airfield traffic pattern, in accordance with some examples of this disclosure. 
         FIG. 12  shows a two-dimensional side view of a baseline protection volume near an airfield traffic pattern, in accordance with some examples of this disclosure. 
         FIG. 13  shows a two-dimensional side view of a modified protection volume based at least in part on a predicted aircraft maneuver near an airfield traffic pattern, in accordance with some examples of this disclosure. 
         FIG. 14  shows a baseline protection volume near an airfield traffic pattern, in accordance with some examples of this disclosure. 
         FIG. 15  shows a two-dimensional top view of a modified protection volume based at least in part on a predicted aircraft maneuver with respect to magnetic north, in accordance with some examples of this disclosure. 
         FIG. 16  shows a two-dimensional top view of a baseline protection volume after completing a turn maneuver, in accordance with some examples of this disclosure. 
         FIG. 17  shows a flowchart for an example technique for determining a modified protection volume, in accordance with some examples of this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Various examples are described below generally directed to devices, systems, and methods for aircraft maneuver prediction, and protection volumes airspace violations based at least in part on the aircraft maneuver prediction. The aircraft maneuver prediction by a system of this disclosure may include predicting future aircraft trajectories based at least in part on any of a wide variety of air traffic protocols or other sources of air traffic information, as further described below. The system may then modify a baseline protection volume based at least in part on a predicted future aircraft maneuver. 
       FIG. 1  depicts a conceptual block diagram of an example air traffic data system  100  that includes a Traffic Collision Avoidance System (TCAS) computer  102 . Air traffic data system and TCAS computer  102  may be incorporated as part of the avionics on an aircraft, or may be implemented in a ground station, in various examples. Although described in terms of aircraft, the principles of this disclosure applies to all vehicles, including land vehicles such as automobiles and water vehicles such as ships. TCAS computer  102  includes an Airborne Surveillance and Separation Assurance Processing (ASSAP) tracker  104  and Traffic Situation Awareness and Alert (TSAA) system  106 . ASSAP tracker  104  may receive (also referred to herein as collect) surveillance data regarding an ownship and other aircraft. TSAA system  106  includes a conflict detector unit  132  including aircraft maneuver prediction unit  134 . Aircraft maneuver prediction unit  134  may predict future aircraft maneuvers based at least in part on surveillance data any of a wide variety of air traffic protocols or other sources of air traffic information. Aircraft maneuver prediction unit  134  may also determine a protection volume and an output based at least in part on the predicted future aircraft maneuvers. 
     As shown in  FIG. 1 , ASSAP tracker  104  interfaces with and uses TSAA system  106 . TSAA system  106  may in some examples be implemented at least in part as a software package or software library comprising computer-executable instructions stored on and/or executed by TCAS computer  102 , as well as data stored and/or processed at least in part by TCAS computer  102 . TSAA system  106  may also be implemented in hardware or firmware in some examples. Air traffic data system  100  and TCAS computer  102  may also include various other systems and components beyond those shown in  FIG. 1  and described below. TCAS computer  102  and/or TSAA system  106  may comprise one or more processors configured to implement the techniques of this disclosure. 
     A flight crew of an aircraft, which may include air traffic data system  100  in some examples, may fly the aircraft in accordance with established guidelines, which may be defined by an entity and followed by aircraft flying within certain regions. For example, the Radio Technical Commission for Aeronautics (RTCA) is an entity that defines Minimum Operational Performance Standards (MOPS or MPS) for General Aviation (GA) aircraft in the United States, including standard DO-317B, which corresponds in Europe to the ED-194 standard defined by European Organisation for Civil Aviation Equipment (Eurocae)). The DO-317B standard includes functionality specifications for Aircraft Surveillance Applications (ASA). In some examples, ASSAP tracker  104  using TSAA system  106  of  FIG. 1  may fulfill the ASA functionality specifications of the DO-317B standard, and may also provide additional performance advantages that go beyond the Minimum Performance Standards defined by DO-317B. In other examples, ASSAP tracker  104  may fulfill other functionality specifications of other standards, such as the ED-194 standard or other standards for other regions. 
     ASSAP tracker  104  may determine, based at least in part on incoming target aircraft information  112 , an estimated target aircraft state for each of one or more target aircraft within a selected range or vicinity, where the target aircraft state may include position, altitude, and velocity (both speed and vector of velocity). In some examples, ASSAP tracker  104  may determine and maintain a determined trajectory or track for each of the one or more target aircraft for as long as they remain active targets for tracking, e.g., they remain airborne and within a selected range or within a selected range of an airport proximate the aircraft (the “ownship”) that includes air traffic data system  100  or with which system  100  is associated if system  100  is not located onboard an aircraft. ASSAP tracker  104  may also maintain extrapolated, predicted future trajectories or tracks for the ownship and all applicable target aircraft out to a selected common point in time in the future, and update those predicted tracks at a selected frequency, e.g., one hertz. 
     As noted above for air traffic data system  100  and TCAS computer  102 , ASSAP tracker  104  and TSAA system  106  may be implemented on an aircraft or at a ground station. ASSAP tracker  104  may receive or collect, via transceiver  115  in air traffic data system  100  or another transceiver, target aircraft information  112  from one or more surrounding aircraft, which may be referred to as target aircraft, as inputs via an automatic dependent surveillance-broadcast (ADS-B) In Receiver and/or other surveillance data sources. Transceiver  115  is configured to receive information from one or more aircraft or other entities, and may include a network interface card (e.g., an Ethernet card), wireless Ethernet network radios (e.g., WiFi), cellular data radios, as well as universal serial bus (USB) controllers, optical transceivers, radio transceivers, or the like. Target aircraft information  112  may include air-to-air ADS-B reports, automatic dependent surveillance-rebroadcast (ADS-R), traffic information service—broadcast (TIS-B), active TCAS surveillance, and/or other sources of information on other aircraft. ASSAP tracker  104  may also receive ownship information  114  (information on the subject aircraft that hosts air traffic data system  100 , if ASSAP tracker  104  is implemented on an aircraft as opposed to a ground station), as inputs. Ownship information  114  may originate from ADS-B reports or TCAS surveillance data that is available to air traffic data system  100 . ASSAP tracker  104 , or TSAA system  106 , may use ownship information  114  to determine a location and a course of the ownship. ASSAP tracker  104  may also use data from other sources, such as a compass or sensors on the ownship, to determine the location and the course of the ownship. 
     The example of  FIG. 1  is further discussed in context of an ASSAP tracker  104  and TSAA system  106  implemented on a subject aircraft that incorporates air traffic data system  100  (the ownship) and evaluating information for the ownship as well as one or more target aircraft. ASSAP tracker  104  may process those inputs, and output aircraft states  122 , including target aircraft states and ownship aircraft states, specifying location or position, course or trajectory, and altitude information for the one or more target aircraft and the ownship, to TSAA system  106 . An example of a flight context for aircraft maneuver prediction is discussed further below with reference to  FIG. 2 . 
     TSAA system  106  receives aircraft states  122  from ASSAP tracker  104  as inputs. TSAA system  106  includes a conflict detector unit  132  and a protocol data store  136 . Conflict detector unit  132  includes aircraft maneuver prediction unit  134 . Conflict detector unit  132  may interact with protocol data store  136  and use aircraft maneuver prediction unit  134 , and potentially additional units or modules, to perform calculations based at least in part on aircraft states  122  and determine whether there is an imminent risk of two aircraft entering each other&#39;s protection volume or protected airspace (or coming too close to each other, as further described below). The protection volume may be defined relative to the respective aircraft and may define a volume of space around the aircraft. The protection volume may also be referred to as a protected airspace zone. When conflict detector component  132  makes a determination of an imminent risk of a protection volume violation, TSAA system  106  may generate, via output node  141 , one or more alert outputs  142  of TSAA system  106  to ASSAP tracker  104 . The alert outputs  142  generated by TSAA system  106  may indicate target aircraft alert states and alert levels for one or more specific target aircraft, in some examples. 
     ASSAP tracker  104  may then generate and output one or more alerts  144 , e.g., to a pilot or flight crew of the ownship, based on the alert outputs  142  that ASSAP tracker  104  receives from TSAA system  106 . ASSAP tracker  104  may output alerts  144  to audio and/or video output interfaces of air traffic data system  100 , such as a display and a loudspeaker of the aircraft (e.g., a display in Class II systems and a loudspeaker in Class I or II systems), and/or other systems, components, or devices to which air traffic data system  100  may be operably connected. The alerts  144  generated by ASSAP tracker  104  may also include indications of target aircraft alert states and alert levels for one or more specific target aircraft, based on information in the alert outputs  142  from TSAA system  106 , in some examples. Additional details of TSAA system  106  are further described below. 
     The baseline protection volume of a GA aircraft in flight proximate to an airport may be within five hundred feet (about one hundred and fifty-two meters) horizontal and two hundred feet (about sixty-one meters) vertical of the aircraft, in some examples. The baseline protection volume may differ for a GA aircraft in cruise or a GA aircraft taking off. The baseline protection volume may decrease when the aircraft is near an airport to prevent nuisance alerts. In some examples, the minimum horizontal radius may be seven hundred and fifty feet horizontally and four hundred and fifty feet vertically. ASSAP tracker  104  may recompute target aircraft and ownship states and output the recomputed or updated aircraft states  122  to TSAA system  106  at a rate of at or approximately one hertz or once per second, in some examples. ASSAP tracker  104  using TSAA system  106  may be specified to generate an alert when there is a risk of a protection volume violation (or intrusion) within twenty to thirty-five seconds of the predicted protection volume violation, for example, such that generating an initial alert less than twenty seconds prior to the predicted protection volume violation would be considered as a late alert or missed alert, in some examples. 
     TSAA system  106  may both track protection volumes around one or more target aircraft and the ownship, and perform trajectory predictions for the one or more target aircraft and the ownship. TSAA system  106  may implement alerting decision logic based on both the protection volumes and the predicted trajectories of each of one or more target aircraft and the ownship. TSAA system  106  may use the position, altitude, and velocity (both speed and vector of velocity) of each of one or more target aircraft and the ownship as inputs in making its determinations of whether to trigger an alert and potentially what information to include in an alert. Conflict detection unit  132  may propagate trajectories of the ownship and target aircraft to establish baseline protection volumes based on location, course, speed, and altitude of each aircraft. Conflict detection unit  132  may also establish horizontal and vertical protection volumes for each propagated node based on trajectory and closure rates between aircraft. TSAA system  106  may generate an alert based on determining that the propagated trajectory for the ownship is on course to enter the modified protection volume of a target aircraft. 
     In accordance with the techniques of this disclosure, aircraft maneuver prediction unit  134  may predict a future aircraft maneuver based at least in part on at least in part on the location and course of the aircraft determined by ASSAP tracker  104 . In some examples, the location of an aircraft may include the latitude, longitude, and altitude. The location may also include the location relative to another point, such as an airport, airstrip, or a landing pad. The course of the aircraft may include the heading, track, and/or route of the aircraft, as well as the vertical and/or horizontal velocity of the aircraft. ASSAP tracker  104 , or TSAA system  106  in some examples, may determine the location and the course of the aircraft based on surveillance data from ADS-B or TCAS. 
     Aircraft maneuver prediction unit  134  may also predict the future aircraft maneuver based at least in part on protocol data from protocol data store  136 . Protocol data store  136  may store data relating to standard procedures such as federal aviation regulations and airfield traffic patterns for GA aircraft. Aircraft maneuver prediction unit  134  may correlate aircraft turns with airport traffic patterns based on the Radio Technical Commission for Aeronautics (RTCA) specification DO-317B algorithm to avoid wrap-around issues. The standard procedures may also include speeds and accelerations for landing and takeoff, as well as standard altitudes for cruising, flare maneuvers, and takeoff roll. Protocol data store  136  may make this data available to aircraft maneuver prediction unit  134 . Aircraft maneuver prediction unit  134  may apply a filter involving velocity trending information to propagate trajectory and improve conflict detection. Example details of airplane maneuvers and trajectory propagation may be found in U.S. Patent Application entitled “AIRCRAFT MANEUVER DATA MANAGEMENT SYSTEM,” filed Oct. 19, 2015, having application Ser. No. 14/886,982, which is incorporated herein by reference in its entirety. 
     Conflict detector unit  132  may use the predicted future aircraft maneuver to determine a protection volume that is modified relative to a baseline protection volume for the ownship or a target aircraft. The baseline protection volume may depend on the trajectory of the aircraft and whether the aircraft is taking off, cruising, or landing. The baseline protection volume may also depend on whether the aircraft is near an airport. The modified protection volume may be larger than the baseline protection volume in a vertical and/or horizontal direction. In some examples, the modified protection volume may expand in the direction of the predicted future aircraft maneuver. 
     ASSAP tracker  104  may generate an output, such as alert  144 , based on the modified protection volume. Alert  144  may be based on the presence of a target aircraft in the modified protection volume determined by conflict detector unit  132 . The output may also be a graphical user interface feature that displays the modified protection volume to a flight crew member, a ground crew member, an air traffic controller, or another user. 
       FIG. 2  depicts an example functional block diagram of an example TSAA system  106  with additional detail in accordance with illustrative examples in which conflict detector unit  132  includes aircraft maneuver prediction unit  134 , as shown in  FIG. 1 . Conflict detector unit  132  includes aircraft maneuver prediction unit  134  as part of protection volume modification unit  146 , in this example. Conflict detector unit  132  also has access to protocol data store  136 , and baseline protection volume unit  140 , as shown in  FIG. 2 . Conflict detector unit  132  is configured to receive aircraft states  122  as inputs, determine and possibly modify a protection volume, determine whether there are any predictions of protection volume violations (as further described below), and generate alert outputs  142  based on those determinations, as described above with reference to  FIG. 1 . 
     Baseline protection volume unit  140  may receive the aircraft state input  122 , which may include the trajectory, location, and speed of the ownship or a target aircraft. Baseline protection volume unit  140  may perform constant trajectory, constant turn rate, and varying turn rate methods, which may extrapolate current straight trajectories, current constant turn rates, and current varying turn rates of a subject aircraft, respectively to predict the trajectory of the aircraft. Baseline protection volume unit  140  may determine a baseline protection volume based on the trajectory, location, altitude, and speed of the aircraft, as well as the presence of any nearby airports. Baseline protection volume unit  140  may create a baseline protection volume for the ownship or a target aircraft by applying the aircraft state data to one or more algorithms in stored in TSAA system  106 . The algorithms may result in a larger baseline protection volume for higher speeds and remoteness from an airport and a smaller baseline protection volume for lower speeds and proximity to an airport. Baseline protection volume unit  140  may output a baseline protection volume to protection volume modification unit  146 . 
     Protection volume modification unit  146  may modify the baseline protection volume based at least in part on a predicted aircraft maneuver, as determined by aircraft maneuver prediction unit  134 , which may include aircraft maneuver information  138 . Aircraft maneuver information  138 , in algorithmic and/or data store implementation, may incorporate any of the following examples of procedural or flight protocol information sources (as partially shown in  FIG. 2 ): standard traffic pattern operations as may be encoded or described in any of various references; the Airport/Facility Directory (A/FD) as published by the U.S. Department of Transportation or another entity; U.S. Federal Aviation Administration (FAA) Airport Diagrams or airport diagrams from another entity; commercial navigation databases and/or data stores, which may include airport configuration information and airport runway configuration information, and/or one or more subsets of or interfaces with such commercial navigation databases and/or data stores; an autonomous airport configuration recognition system implemented by onboard systems; and/or other protocols, rules, airfield traffic patterns, airport-applicable standard operating procedures (SOPs), standard piloting practices, flight operation reference information, or other patterns or conventions of general aviation piloting, for example, all of which may be collectively referred to as “protocol data” for purposes of this disclosure (e.g., aircraft maneuver information  138  of  FIG. 2 ). 
     Aircraft maneuver prediction unit  134  may also apply, e.g., algorithmic means of simplifying criteria and/or logic applicable to aircraft maneuver prediction based on data or information from any aircraft maneuver information sources, including those listed above. Similarly, for purposes of this disclosure, “aircraft maneuver prediction” may collectively refer to trajectory prediction (e.g., by aircraft maneuver prediction unit  134 ) based at least in part on aircraft maneuver information (e.g., aircraft maneuver information  138 ) as opposed to simple constant straight trajectory, constant turn rate, and/or constantly varying track angle (e.g., which may be computed or implemented by other elements of baseline protection volume unit  140 ). “Standard procedures” may refer to the maneuvers incorporated in protocol data, such as the turns, changes in altitude, accelerations, and threshold velocities that an aircraft may likely perform in order to operate safely or comply with regulations. 
     Aircraft maneuver prediction unit  134  may incorporate aircraft maneuver information  138  directly in algorithms of its executable instructions, in some examples. Aircraft maneuver prediction unit  134  may also incorporate or interface with aircraft maneuver information  138  in the form of an aircraft maneuver information data store that may store either all or some (e.g., an auxiliary set) of the aircraft maneuver information, in some examples. In some examples in which an aircraft maneuver information data store is used, the aircraft maneuver information data store may be implemented as an in-memory data cache to avoid buffering latency for real-time operating performance, e.g., to implement assured execution times in a selected fraction of a second, to support one-hertz update rates for aircraft trajectories and airspace violation determinations. Aircraft maneuver prediction unit  134  may incorporate aircraft maneuver information  138  as either or both of direct algorithmic incorporation of aircraft maneuver information and/or accessing an aircraft maneuver information data store, in various examples. In some examples, incorporating aircraft maneuver information  138  directly in algorithms of its executable instructions may allow faster processing speed for aircraft maneuver prediction unit  134 , while in some examples, implementing the aircraft maneuver information  138  in a data store (e.g., an in-memory data cache system such as Redis, Memcached, etc.) may enable more flexibility and ease of adding to or modifying the aircraft maneuver information. In various examples, aircraft maneuver prediction unit  134  may comply with the RTCA DO-178B standard, Software Considerations in Airborne Systems and Equipment Certification. 
     While performing aircraft maneuver prediction using aircraft maneuver information, TSAA system  106  of this disclosure may predict a wide variety of future changes in the trajectory or trajectories of one or more aircraft based on realistic assessments of future changes in trajectories based on the aircraft maneuver information. The aircraft maneuver information may enable TSAA system  106  to propagate (or predict) a flight path of a target aircraft more accurately compared to examples in which the flight path of a target aircraft is predicted without consideration of the procedural behavior of aircraft. TSAA system  106  of this disclosure performing aircraft maneuver prediction using aircraft maneuver information may achieve a substantially higher accuracy in generating protected airspace violation alerts, relative to other air traffic alert systems. The improved accuracy of alerts of TSAA system  106  of this disclosure may include both a higher percentage of alerts generated when proper, as well as a reduced percentage of false positives, or nuisance alerts, that may be frequently generated by some air traffic alert systems. 
     For example, when an air traffic alert system determines a protection volume, the system may base the protection volume on the current trajectory and one or more current aircraft maneuvers. The current trajectory and current aircraft maneuvers may not indicate future aircraft maneuvers, which may involve the aircraft changing course or changing altitude outside of the baseline protection volume. As a result, a baseline protection volume may not account for the future movement of the aircraft. In contrast, TSAA system  106  of this disclosure may modify the baseline protection volume to account for future aircraft maneuvers, e.g., by predicting the future aircraft maneuvers based at least in part on the location and course of the aircraft, as well as data relating to standard procedures. Thus, TSAA system  106  may increase the accuracy of alerts of possible collisions before the aircraft begins a predicted future aircraft maneuver, relative to other TSAA algorithms. For example, TSAA system  106  may modify the baseline protection volume for an aircraft on a runway when the aircraft reaches a threshold velocity that is associated with takeoff. In such an example, a modified baseline protection volume may be larger than the baseline protection volume in the upward vertical direction when the predicted future aircraft maneuver is a takeoff. If conflict detector unit  132  in TSAA system  106  determines that an aircraft or obstacle may infringe the modified protection volume, conflict detector unit  132  may generate an alert output  142  via output node  141 . 
       FIG. 3  depicts an example takeoff maneuver for an aircraft  150 , in accordance with some examples of this disclosure.  FIG. 3  depicts aircraft  150  as a helicopter, but aircraft  150  may be any suitable type of aircraft that executes a takeoff maneuver similar to the maneuver shown in  FIG. 3 . Surface  152  may be a landing pad, a helipad, a runway, an airstrip, roadway, or any other surface for takeoff. Helicopter Flying Handbook, FAA-H-8083-21A, chapter nine, includes further details on basic flight maneuvers. 
     Time  154  may correspond to zero seconds. The example takeoff maneuver in  FIG. 3  is depicted as having a duration of four seconds. In some examples, the example takeoff maneuver may have a longer or shorter duration. The window size for trajectory propagation may be set to thirty-five seconds according to MOPS. At time  154 , aircraft  150  may be elevated above surface  152  with zero horizontal velocity and nearly zero vertical velocity. At time  154 , aircraft  150  may be hovering above surface  152 . 
     At time  156 , the horizontal velocity of aircraft  150  may increase rapidly. The vertical velocity of aircraft  150  may be near zero or slightly positive. For purposes of this disclosure, a positive vertical velocity may indicate that the altitude of aircraft  150  is increasing. At time  158 , the horizontal velocity of aircraft  150  may remain similar to the horizontal velocity at time  156 . The vertical velocity and altitude of aircraft  150  at time  158  may increase at time  158 , as compared to times  154 ,  156 . 
     At time  160 , the horizontal velocity of aircraft  150  may remain similar to the horizontal velocity at times  156 ,  158 . In some examples, the horizontal velocity of aircraft  150  may increase or decrease at time  160  but still remain positive. The vertical velocity of aircraft  150  at time  160  may remain similar or increase further such that the altitude at time  160  is higher than the altitude at times  156 ,  158 . 
     At time  162 , the horizontal velocity of aircraft  150  may remain similar to the horizontal velocity at times  158 ,  160 . In some examples, the horizontal velocity of aircraft  150  may increase or decrease at time  162  but still remain positive. The vertical velocity of aircraft  150  at time  162  may remain similar or increase further so that the altitude at time  162  is higher than the altitude at times  158 ,  160 . 
     In the context of this disclosure,  FIG. 3  may depict a takeoff maneuver as a standard procedure. At time  154 , TSAA system  106  may predict that the horizontal velocity of aircraft  150  may increase, even though the horizontal velocity at time  154  may be at or near zero. TSAA system  106  of this disclosure may determine the vertical velocity of aircraft  150  at or just before time  154  and determine that the vertical velocity exceeds a threshold vertical velocity. TSAA system  106  may determine that aircraft  150  has not started the predicted future aircraft maneuver by determining that the horizontal velocity at time  154  is at or near zero. TSAA system  106  may consequently determine a modified protection volume with a larger horizontal dimension relative to the baseline protection volume to account for the predicted future increase in horizontal velocity that may be associated with takeoff of aircraft  150 . TSAA system  106  thus determines a modified protection volume for the aircraft that is modified relative to the baseline protection volume by increasing a horizontal dimension of the protection volume relative to the baseline protection volume, based at least in part on the predicted future aircraft maneuver of an increase in horizontal velocity. 
       FIG. 4  depicts a graph  170  of vertical velocity  176 , horizontal velocity  178 , and altitude  180  for an aircraft during takeoff, in accordance with some examples of this disclosure. Vertical velocity  176 , horizontal velocity  178 , and altitude  180  in graph  170  may be approximations that correspond to positions and velocities of aircraft  150  at times  154 - 162  in  FIG. 3 . For example, times  182 ,  184 ,  186 ,  188 ,  190  may correspond to times  154 ,  156 ,  158 ,  160 ,  162  in  FIG. 3 . 
     The horizontal axis of graph  170  may correspond to time. Vertical axis  172  may correspond to values for vertical velocity  176  and altitude  180 . Vertical axis  174  may correspond to values for horizontal velocity  178 . At time  182 , the aircraft may be hovering, meaning that vertical velocity  176  and horizontal velocity  178  are near zero. At time  184 , the aircraft may maintain a near-zero altitude  180 , but horizontal velocity may increase rapidly. At times  186 ,  188 ,  190 , horizontal velocity  178  and altitude  180  may increase as the aircraft takes off. 
     TSAA system  106  may predict a future aircraft maneuver at time  182 . The predicted future aircraft maneuver may be an increase in horizontal velocity. TSAA system  106  may base the prediction on determining that vertical velocity  176  at time  182  exceeds a threshold vertical velocity and that the aircraft has not started the predicted future aircraft maneuver. TSAA system  106  may modify a baseline protection volume by increasing a horizontal dimension of the baseline protection volume. 
     TSAA system  106  may also predict a future aircraft maneuver at time  184 . The predicted future aircraft maneuver may be an increase in vertical velocity. TSAA system  106  may base the prediction on determining that horizontal velocity  178  at time  182  exceeds a threshold horizontal velocity and that the aircraft has not started the predicted future aircraft maneuver. TSAA system  106  may modify a baseline protection volume by increasing a vertical dimension of the protection volume, thereby determining a modified protection volume for the aircraft. TSAA system  106  thus determines a modified protection volume for the aircraft that is modified relative to the baseline protection volume by increasing a vertical dimension of the protection volume relative to the baseline protection volume, based at least in part on the predicted future aircraft maneuver of an increase in vertical velocity. 
       FIG. 5  depicts trajectory propagation for an aircraft using constant velocity, in accordance with some examples of this disclosure. TSAA system  106  or ASSAP tracker  104  may determine the location and course of the aircraft. TSAA system  106  may determine a future position of the aircraft based at least in part on the current velocity, assuming no turns and no acceleration.  FIG. 5  may depict the protection volume as a circle at times  200 - 205 , but the protection volume may be another shape or may vary in some examples. 
       FIG. 6  depicts trajectory propagation for an aircraft using an intention-based predictive algorithm, in accordance with some examples of this disclosure. TSAA system  106  or ASSAP tracker  104  may determine the location and course of the aircraft. TSAA system  106  may determine a future position based at least in part on the current velocity and a set of protocol data indicating one or more standard procedures for one or more aircraft maneuvers. In the example of  FIG. 6 , the aircraft maneuver may be takeoff, and the standard procedure may be to accelerate at a constant rate. As a result, trajectory propagation may predict that the velocity of the aircraft will continue to increase during times  210 - 215 . 
       FIG. 7  depicts trajectory propagation for an aircraft using a threshold velocity to reduce acceleration, in accordance with some examples of this disclosure. During times  220 - 222 , the aircraft may accelerate at a constant rate a 2 . At time  224 , TSAA system  106  may determine that the velocity exceeds a threshold velocity V T . At time  224 , TSAA system  106  may reduce the predicted acceleration from a 2  to a 3 , which may be less than half of a 2 . A set of protocol data indicating standard procedures for aircraft maneuvers may include the numerical value of the threshold velocity. In some examples, the aircraft maneuver may be takeoff, and the standard procedure may be acceleration to a threshold horizontal velocity before reducing acceleration at times  224 - 226 . 
     The acceleration may reduce to zero as the aircraft reaches cruise velocity of approximately one hundred and forty knots in the example of a helicopter. For some examples involving helicopters, TSAA system  106  may refrain from increasing the vertical dimension of the protection volume because takeoff, hovering taxi, and air taxi may exhibit similar maneuvers. In order to prevent nuisance alerts, TSAA system  106  may refrain from enlarging the protection volume in certain circumstances. 
       FIG. 8  depicts a two-dimensional side view of a modified protection volume based at least in part on a predicted future aircraft maneuver, in accordance with some examples of this disclosure. Trajectory propagation in  FIG. 8  may be similar to trajectory propagation in  FIG. 7  such that the acceleration decreases when the velocity exceeds a threshold velocity. 
     TSAA system  106  may determine a baseline protection volume when the horizontal velocity of an aircraft is less than the threshold horizontal velocity, such as at times  230 - 232 . If TSAA system  106  determines that the velocity exceeds the threshold velocity, such as at times  234 - 236 , TSAA system  106  may determine a modified protection volume. TSAA system  106  may also base a predicted future aircraft maneuver on a propagated trajectory of the aircraft, which TSAA system  106  may base at least in part on the acceleration of the aircraft. TSAA system  106  may propagate a trajectory for the aircraft based on current and expected future acceleration of the aircraft, as well as the location and the course of the aircraft. The modified protection volume may be larger than the baseline protection volume in the vertical dimension. TSAA system  106  may predict that the aircraft will increase altitude during takeoff after reaching a threshold horizontal velocity. TSAA system  106  may access protocol data for a standard procedure such as takeoff, and the standard procedure may include the aircraft increasing altitude after the horizontal velocity exceeds a threshold horizontal velocity. 
     In some examples, a fixed wing aircraft may employ an acceleration process on a runway during takeoff. The vertical velocity may be at or near zero until the aircraft reaches a threshold horizontal velocity. The aircraft is unlikely to lift off the runway when the horizontal velocity is less than the threshold. However, a takeoff from a soft field may include a lower threshold horizontal velocity followed by lower vertical velocity just after liftoff until the aircraft reaches a threshold vertical velocity or threshold angle. The threshold horizontal velocity for a helicopter may be sixteen to twenty-four knots to reach effective translational lift. The threshold horizontal velocity may be higher, such as thirty to sixty knots, based on a variety of factors. 
       FIG. 9  depicts a two-dimensional side view of a baseline protection volume after a predicted future aircraft maneuver has started, in accordance with some examples of this disclosure. The aircraft maneuver may be an increase in altitude as the aircraft takes off a runway, an airstrip, or the like. 
     TSAA system  106  may determine a course and location of the aircraft at time  240 . TSAA system  106  may determine that the aircraft has positive vertical velocity, i.e., increasing altitude. At time  240 , TSAA system  106  may determine that the aircraft has started a predicted aircraft maneuver (i.e., positive vertical velocity and increasing altitude). Based at least in part on the determination that the aircraft has started a predicted aircraft maneuver, TSAA system  106  may switch from generating an output based on the modified protection volume (see  FIG. 8 ) to generating an output based on a baseline protection volume and generate an output based on the baseline protection volume, such as an alert or a display for flight crew or ground crew. The output may also include data for transmission to an aircraft or a recipient on the ground. TSAA system  106  may continue to generate outputs based on the baseline protection volume at times  241 - 245 . The baseline protection volume may adequately protect the aircraft if the course and acceleration of the aircraft remain constant at times  241 - 245 . 
       FIG. 10  shows a conceptual perspective diagram of an airfield traffic pattern for a runway  510 , in accordance with some examples of this disclosure. Airplane Flying Handbook, FAA-H-8083-3A, chapter seven, includes details on airport traffic patterns.  FIG. 10  shows airport airspace  500  around a general aviation (GA) airport with ownship  502  and target aircraft  504 , in flight in accordance with a standard procedural flight pattern as may be predicted by TSAA system  106 . Wind direction  509  may be parallel to runway  510  with downwind to the left relative to an observer at airport terminal  508 , indicating a left-turn air traffic configuration according to procedural air traffic standards (to ensure takeoff into the wind). In cases where the wind direction is opposite to wind direction  509  of this example, procedural flight standards may indicate similar flight patterns but in opposite directions, in a right-turn air traffic configuration. Ownship  502  may enter the procedural pattern at entry turn  512 , placing ownship  502  in downwind track  514  behind target aircraft  504 . Standard flight procedure may indicate for target aircraft  504  and ownship  502  to follow downwind track  514 , base turn  516  into base track  518 , and final approach turn  520  to final approach  522  and landing  523 , along with steadily reducing speed along this path. In some examples, if an aircraft is not aligned with the centerline of runway  510  during an approach, the aircraft may level out at a traffic pattern altitude for the class associated with the aircraft. 
     Standard flight procedure for aircraft taking off from runway  510  may include accelerating along track  523  to lift off into departure track  524 . Depending on its intended heading, an aircraft in takeoff may continue ascending along a straight line path  526 , a shallow turn  528 , or a crosswind turn  530  into crosswind track  532 , and a subsequent left turn  534  if continuing on a heading opposite to the direction of takeoff.  FIG. 10  also shows path  540  as the ground track below and corresponding to the procedural flight tracks  512 - 534 . Aircraft in flight in airspace  500  may be guided by an air traffic control (ATC) tower, or in airports without an ATC tower, the aircraft may fly in accordance with visual acquisition and observation of other aircraft traffic and adherence to standard flight rules and other procedures, such as pursuing the flight tracks  512 - 534  as described above and maintaining minimum separations from any surrounding target aircraft. 
     In some circumstances, aircraft  502  and  504  may follow tracks  514 ,  516 ,  518 ,  520 ,  522 , and  523  in order and separated by a standard procedural separation distance along tracks  514 - 523  throughout the process; while in other circumstances, some deviations from both aircrafts&#39; adherence to this sequence of tracks may occur. In one example without any deviations, aircraft  502  and  504  may begin from the positions as shown in  FIG. 10  at a minimum standard procedural separation from each other, when target aircraft  504  begins executing base leg turn  516 . Target aircraft  504  may be flying at a lower speed than ownship  502  since it is further along in the process of decelerating for its landing. 
     As aircraft  502  and  504  approach base leg turn  516 , TSAA system  106  may predict base leg turn  516  as a future aircraft maneuver for aircraft  502  and/or  504 . TSAA system  106  may base the prediction of base leg turn  516  on the location and course of aircraft  502  and  504  relative to runway  510 . TSAA system  106  may also base the prediction of base leg turn  516  on a set of protocol data indicating standard procedures, such as an airfield traffic pattern, for one or more aircraft maneuvers, such as landing. The protocol data may include the dimensions of runway  510  and the dimensions of path  540 . TSAA system  106  may determine a modified protection volume based at least in part on the predicted aircraft maneuver (i.e., base leg turn  516 ) and generate an output based on the modified protection volume. In some examples, the modified protection volume may be larger than a baseline protection volume in a horizontal dimension to account for the predicted base leg turn  516 . 
       FIG. 11  shows a two-dimensional top view of a modified protection volume based at least in part on a predicted aircraft maneuver near airfield traffic pattern  550 , in accordance with some examples of this disclosure. Airfield traffic pattern  550  may include path  540  over runway  510 . Path  540  may be rectangular and may extend past the ends of runway  510  so that aircraft can takeoff from and land at runway  510 . 
     At times  552 - 554 , TSAA system  106  may determine the location and course of an aircraft relative to runway  510 . TSAA system  106  may also determine a current aircraft maneuver, which may comprise a lack of turns at times  552 - 558 . TSAA system  106  may refrain from predicting a horizontal turn at times  552 - 554  or at time  556  because the aircraft is abeam runway  510 , or has not passed the end of runway  510 .  FIG. 11  may depict the baseline protection volume at times  552 - 554  as a circular top view of a cylindrical volume in space, but the baseline protection volume may be any suitable shape for protecting an aircraft. 
     At times  557 ,  558 , TSAA system  106  may predict a left horizontal turn as a future aircraft maneuver, possibly near a forty-five-degree line projected from the end of the runway, where the angle is measured from the centerline of the runway. TSAA system  106  may predict the future aircraft maneuver based at least in part on the course and the location of the aircraft relative to runway  510 . In particular, the aircraft at times  557 ,  558  has passed an end of runway  510  but has not changed course or started the predicted future aircraft maneuver. The modified protection volume at times  557 ,  558  may be a cylindrical volume that is larger than the baseline protection volume, or the modified protection volume may be larger than the baseline protection volume only in the direction of the predicted future aircraft maneuver. 
     For an aircraft at times  552 - 554 , TSAA system  106  may extend the horizontal protection volume to beyond the end of the runway, e.g., the location at time  557 . If TSAA system  106  detects deceleration at times  552 - 554 , TSAA system  106  may predict that the aircraft is preparing to landing after completing the base turns on path  540 . However, if the base turn does not occur, TSAA system  106  may switch back to generating an output based on the baseline protection volume upon determining that the aircraft has exited the airfield traffic pattern. 
       FIG. 12  shows a two-dimensional top view of a baseline protection volume near an airfield traffic pattern, in accordance with some examples of this disclosure. Path  540  may be a rectangular airfield traffic pattern stored in a set of protocol data with one or more aircraft maneuvers, such as horizontal turns. At times  570 - 575 , TSAA system  106  may refrain from predicting a future aircraft maneuver, such as a horizontal turn, based at least in part on determining that the aircraft has already started a horizontal turn. Instead, TSAA system  106  may switch from generating an output based on the modified protection volume to generating an output based on a baseline protection volume for times  570 - 575 . 
       FIG. 13  shows a two-dimensional side view of a modified protection volume based at least in part on a predicted aircraft maneuver near an airfield traffic pattern, in accordance with some examples of this disclosure. At times  580 - 586 , TSAA system  106  may determine the location and course of an aircraft relative to runway  510 . TSAA system  106  may refrain from predicting a horizontal turn at times  580 - 582  or at time  584  because the aircraft is abeam runway  510 , or has not passed the end of runway  510 .  FIG. 13  may depict the baseline protection volume at times  580 - 582 ,  584  as a two-dimensional side view of a cylindrical volume, but the baseline protection volume may be any suitable shape for protecting an aircraft. 
     At times  585 ,  586 , TSAA system  106  may predict a negative vertical velocity (i.e., reduction in altitude) as a future aircraft maneuver. TSAA system  106  may predict the future aircraft maneuver based at least in part on the course and the location of the aircraft relative to runway  510 . TSAA system  106  may also predict the future aircraft maneuver based at least in part on a current aircraft maneuver, which may comprise zero vertical velocity at times  585 ,  586 . In particular, the aircraft at times  585 ,  586  has passed an end of runway  510  but has not changed course or started the predicted future aircraft maneuver. The modified protection volume at times  585 ,  586  may be a cylindrical volume that is larger than the baseline protection volume only in the direction of the predicted future aircraft maneuver, which in the example of  FIG. 13  may be the downward direction. TSAA system  106  may increase the protection volume by, e.g., a few hundred feet in the downward direction in this example, though lesser or greater spatial extensions may be applied in other examples. 
       FIG. 14  shows a two-dimensional side view of a baseline protection volume near an airfield traffic pattern, in accordance with some examples of this disclosure. At times  590 - 595 , TSAA system  106  may refrain from predicting a future aircraft maneuver, such as a negative vertical velocity, based on determining that the aircraft has already started a horizontal turn. Instead, TSAA system  106  may switch from generating an output based on the modified protection volume (see  FIG. 13 ) to generating an output based on a baseline protection volume for times  590 - 595 . 
     In some examples, during a landing maneuver, a helicopter may reduce horizontal velocity to almost zero before touching down. A fixed wing aircraft may touch down at a higher horizontal velocity, as compared to a helicopter. TSAA system  106  may therefore use the aircraft characteristics and surveillance data to predict a landing maneuver. 
       FIG. 15  shows a two-dimensional top view of a modified protection volume based at least in part on a predicted aircraft maneuver with respect to magnetic north  600 , in accordance with some examples of this disclosure. Magnetic north  600  may vary from geographical north in some examples. Many standard procedures are based on a course of an aircraft with respect to magnetic north  600 , such as federal aviation regulations, part  91 , sections  159  and  179 . For example, when the aircraft is cruising under visual flight rules (VFR) at more than three thousand feet above ground level and less than eighteen thousand feet above mean sea level, protocol data may indicate that the aircraft have an altitude at an odd number of thousand feet plus five hundred feet when travelling east relative to magnetic north  600 . When the aircraft is travelling west relative to magnetic north  600 , protocol data may indicate that the aircraft have an altitude at an even number of thousand feet plus five hundred feet. Therefore, when an aircraft turns and changes course relative to magnetic north  600 , TSAA system  106  may predict a change in altitude by one thousand feet. 
     At times  602 ,  603 , TSAA system  106  may determine the course of an aircraft relative to magnetic north  600 . TSAA system  106  may refrain from predicting a horizontal turn at times  602 ,  603  because the course of the aircraft is east relative to magnetic north  600 .  FIG. 15  may depict the baseline protection volume at times  602 ,  603  as a rectangular cross-section of a cylindrical volume, but the baseline protection volume may be any suitable shape for protecting an aircraft. 
     At times  604 - 606 , TSAA system  106  may predict a change in altitude as a future aircraft maneuver. TSAA system  106  may predict the future aircraft maneuver based at least in part on the course of the aircraft relative to magnetic north  600 . In particular, the aircraft at times  604 - 606  may have a course that is west relative to magnetic north  600 , but the aircraft may not have changed altitude to comply with VFR, i.e., the aircraft has not started the predicted future aircraft maneuver. The modified protection volume at times  604 - 606  may be a rectangular cross-section of a cylindrical volume that is larger than the baseline protection volume only in the direction of the predicted future aircraft maneuver, which in the example of  FIG. 15  may be the upward and/or downward directions. Although  FIG. 15  is a two-dimensional top view,  FIG. 15  depicts widened protection volumes at times  604 - 606 . However, the protection volumes at times  604 - 606  may be enlarged in the vertical dimension, i.e., into or out of the page. In some examples, the protection volumes in  FIGS. 15-16  may be a cylindrical volume with the length of the cylinder extending in the vertical direction, as shown in  FIGS. 8-9 and 11-14 . 
       FIG. 16  shows a two-dimensional top view of a baseline protection volume after completing a turn maneuver, in accordance with some examples of this disclosure. At times  610 - 615 , TSAA system  106  may refrain from predicting a future aircraft maneuver, such as a change in altitude, based at least in part on determining that the aircraft has already started to change altitude after having changed course relative to magnetic north  600 . Instead, TSAA system  106  may switch from generating an output based on the modified protection volume (see  FIG. 15 ) to generating an output based on a baseline protection volume for times  610 - 615 . 
       FIG. 17  shows a flowchart for an example technique  700  for determining a modified protection volume, in accordance with some examples of this disclosure. Technique  700  is described with reference to the system of  FIG. 1 , including ASSAP tracker  104  and TSAA system  106 , although other components, such as aircraft maneuver prediction unit  134  in  FIG. 1 or 2 , may perform similar techniques. 
     The technique of  FIG. 17  includes receiving surveillance data from an aircraft ( 702 ). AS SAP tracker  104  may receive surveillance data from ownship  114  and target aircraft  112 . The received surveillance data may originate in ADS-B reports or broadcasts and other data from external sources, as well as data from sensors and compasses. 
     The technique of  FIG. 17  further includes determining a location of the aircraft based at least in part on the received surveillance data ( 704 ). ASSAP tracker  104  may determine the location, which may include latitude, longitude, and altitude. AS SAP tracker  104  may determine the location of the aircraft relative to a runway or another fixed landmark. 
     The technique of  FIG. 17  further includes determining a course of the aircraft based at least in part on the received surveillance data ( 706 ). ASSAP tracker  104  may determine the course, which may include direction, heading, route, and trajectory. ASSAP tracker  104  may determine the course of the aircraft relative to a runway, another fixed landmark, geographical north, or magnetic north. 
     The technique of  FIG. 17  further includes predicting a future aircraft maneuver for the aircraft based at least in part on the location and the course of the aircraft, and based at least in part on a set of protocol data indicating one or more standard procedures for one or more aircraft maneuvers ( 708 ). For example, TSAA system  106  may predict a turn or change in altitude based at least in part on the data received from ASSAP tracker  104 . TSAA system  106  may predict a turn based at least in part on determining that the aircraft has passed the end of a nearby runway and has not started turning yet. 
     The technique of  FIG. 17  further includes determining, based at least in part on the predicted future aircraft maneuver, a modified protection volume for the aircraft that is modified relative to a baseline protection volume for the aircraft ( 710 ). TSAA system  106  may enlarge the baseline protection volume in the direction of the predicted aircraft maneuver. For example, TSAA system  106  may enlarge the protection volume in the vertical dimension after the aircraft changes direction relative to magnetic north and before the aircraft begins the predicted aircraft maneuver. 
     The technique of  FIG. 17  further includes generating an output based at least in part on the modified protection volume ( 712 ). The output may be an alert or display to flight crew, ground crew, air traffic control, or another person. The output may be transmission of data to an external recipient, such as another aircraft or a recipient on the ground, such as air traffic control. 
     The following examples may illustrate one or more of the techniques of this disclosure. 
     Example 1 
     A system is configured to receive surveillance data from an aircraft, determine a location of the aircraft based at least in part on the received surveillance data, and determine a course of the aircraft based at least in part on the received surveillance data. The system is further configured to predict a future aircraft maneuver for the aircraft based at least in part on the location and the course of the aircraft, and based at least in part on a set of protocol data indicating one or more standard procedures for one or more aircraft maneuvers. The system is further configured to determine, based at least in part on the predicted future aircraft maneuver, a modified protection volume for the aircraft that is modified relative to a baseline protection volume for the aircraft. The system is further configured to generate an output based on the modified protection volume. 
     Example 2 
     The system of example 1, further configured to determine a second course of the aircraft at a second time and determine a second location of the aircraft at the second time. The system is further configured to determine, based at least in part on the second course of the aircraft and the second location of the aircraft, that the aircraft has started the predicted future aircraft maneuver. The system is further configured to switch from generating an output based on the modified protection volume to generating an output based on the baseline protection volume based at least in part on determining that the aircraft has started the predicted future aircraft maneuver, and generate a second output based on the baseline protection volume. 
     Example 3 
     The system of example 1 or 2, further configured to determine the course of the aircraft by at least determining a course of the aircraft relative to a runway based at least in part on the received surveillance data. The system is further configured to determine the location of the aircraft by at least determining a location of the aircraft relative to the runway based at least in part on the received surveillance data. 
     Example 4 
     The system of any one of examples 1 to 3, wherein the one or more standard procedures comprises an airfield traffic pattern, and the predicted future aircraft maneuver comprises a turn. The system is further configured to determine that the aircraft has passed an end of the runway, determine that the aircraft has not started the predicted future aircraft maneuver, and determine the modified protection volume with a larger horizontal dimension than the baseline protection volume based at least in part on determining that the aircraft has passed the end of the runway and has not started the predicted future aircraft maneuver. 
     Example 5 
     The system of any one of examples 1 to 4, wherein the one or more standard procedures comprises an airfield traffic pattern, and the predicted future aircraft maneuver comprises a decrease in altitude. The system is further configured to determine that the aircraft has passed an end of the runway, determine that the aircraft has not started the predicted future aircraft maneuver, and determine the modified protection volume with a larger vertical dimension than the baseline protection volume based at least in part on determining that the aircraft has passed the end of the runway and has not started the predicted future aircraft maneuver. 
     Example 6 
     The system of any one of examples 1 to 5, wherein the one or more standard procedures comprises a takeoff, and the predicted future aircraft maneuver comprises an increase in altitude. The system is further configured to determine a horizontal velocity of the aircraft, determine that the horizontal velocity of the aircraft exceeds a threshold horizontal velocity, determine that the aircraft has not started the predicted future aircraft maneuver, and determine the modified protection volume with a larger vertical dimension than the baseline protection volume based at least in part on determining that the horizontal velocity of the aircraft exceeds the threshold horizontal velocity. 
     Example 7 
     The system of any one of examples 1 to 6, wherein the aircraft comprises a helicopter; the one or more standard procedures comprises a takeoff, and the predicted future aircraft maneuver comprises an increase in horizontal velocity. The system is further configured to determine a vertical velocity of the aircraft, determine that the vertical velocity of the aircraft exceeds a threshold vertical velocity, determine that the aircraft has not started the predicted future aircraft maneuver, and determine the modified protection volume with a larger horizontal dimension than the baseline protection volume based at least in part on determining that the horizontal velocity of the aircraft exceeds the threshold vertical velocity. 
     Example 8 
     The system of any one of examples 1 to 7, wherein the one or more standard procedures comprises a turn during cruise, and the predicted future aircraft maneuver comprises a change in altitude. The system is further configured to determine that the course of the aircraft has changed relative to a magnetic north and determine the modified protection volume with a larger vertical dimension than the baseline protection volume based at least in part on determining that the course of the aircraft has changed relative to the magnetic north. 
     Example 9 
     The system of any one of examples 1 to 8, wherein the output comprises an alert in response to a second aircraft being detected inside the modified protection volume. 
     Example 10 
     A method includes receiving surveillance data from an aircraft, determining a location of the aircraft based at least in part on the received surveillance data, and determining a course of the aircraft based at least in part on the received surveillance data. The method further includes predicting a future aircraft maneuver for the aircraft based at least in part on the location and the course of the aircraft, and based at least in part on a set of protocol data indicating one or more standard procedures for one or more aircraft maneuvers. The method further includes determining, based at least in part on the predicted future aircraft maneuver, a modified protection volume for the aircraft that is modified relative to a baseline protection volume for the aircraft and generating an output based on the modified protection volume. 
     Example 11 
     The method of example 10, further comprising determining a second course of the aircraft at a second time, determining a second location of the aircraft at the second time. The method further comprises determining, based at least in part on the second course of the aircraft and the second location of the aircraft, that the aircraft has started the predicted future aircraft maneuver. The method further comprises switching from generating an output based on the modified protection volume to generating an output based on the baseline protection volume based at least in part on determining that the aircraft has started the predicted future aircraft maneuver, and generating a second output based on the baseline protection volume. 
     Example 12 
     The method of example 10 or 11, further comprising determining the course of the aircraft by at least determining a course of the aircraft relative to a runway based at least in part on the received surveillance data and determining the location of the aircraft by at least determining a location of the aircraft relative to the runway based at least in part on the received surveillance data. 
     Example 13 
     The method of any one of examples 10 to 12, wherein the one or more standard procedures comprises an airfield traffic pattern, the predicted future aircraft maneuver comprises a turn. The method further includes determining that the aircraft has passed an end of the runway, determining that the aircraft has not started the predicted future aircraft maneuver, and determining the modified protection volume with a larger horizontal dimension than the baseline protection volume based at least in part on determining that the aircraft has passed the end of the runway and has not started the predicted future aircraft maneuver. 
     Example 14 
     The method of any one of examples 10 to 13, wherein the one or more standard procedures comprises an airfield traffic pattern, the predicted future aircraft maneuver comprises a decrease in altitude. The method further includes determining that the aircraft has passed an end of the runway, determining that the aircraft has not started the predicted future aircraft maneuver, and determining the modified protection volume with a larger vertical dimension than the baseline protection volume based at least in part on determining that the aircraft has passed the end of the runway and has not started the predicted future aircraft maneuver. 
     Example 15 
     The method of any one of examples 10 to 14, wherein the one or more standard procedures comprises a takeoff, and the predicted future aircraft maneuver comprises an increase in altitude. The method further includes determining a horizontal velocity of the aircraft; determining that the horizontal velocity of the aircraft exceeds a threshold horizontal velocity, determining that the aircraft has not started the predicted future aircraft maneuver, and determining the modified protection volume with a larger vertical dimension than the baseline protection volume based at least in part on determining that the horizontal velocity of the aircraft exceeds the threshold horizontal velocity. 
     Example 16 
     The method of any one of examples 10 to 15, wherein the aircraft comprises a helicopter, the one or more standard procedures comprises a takeoff, and the predicted future aircraft maneuver comprises an increase in horizontal velocity. The method further includes determining a vertical velocity of the aircraft, determining that the vertical velocity of the aircraft exceeds a threshold vertical velocity. The method further includes determining that the aircraft has not started the predicted future aircraft maneuver, and determining the modified protection volume with a larger horizontal dimension than the baseline protection volume based at least in part on determining that the horizontal velocity of the aircraft exceeds the threshold vertical velocity. 
     Example 17 
     The method of any one of examples 10 to 16, wherein the one or more standard procedures comprises a turn during cruise, and the predicted future aircraft maneuver comprises a change in altitude. The method further includes determining that the course of the aircraft has changed relative to a magnetic north and determining the modified protection volume with a larger vertical dimension than the baseline protection volume based at least in part on determining that the course of the aircraft has changed relative to the magnetic north. 
     Example 18 
     The method of any one of examples 10 to 17, wherein the output comprises an alert in response to a second aircraft being detected inside the modified protection volume. 
     Example 19 
     A system comprises means for receiving surveillance data from an aircraft. The system further comprises means for determining a location of the aircraft based at least in part on the received surveillance data and means for determining a course of the aircraft based at least in part on the received surveillance data. The system further comprises means for predicting a future aircraft maneuver for the aircraft based at least in part on the location and the course of the aircraft, and based at least in part on a set of protocol data indicating one or more standard procedures for one or more aircraft maneuvers. The system further comprises means for determining, based at least in part on the predicted future aircraft maneuver, a modified protection volume for the aircraft that is modified relative to a baseline protection volume for the aircraft and means for generating an output based on the modified protection volume. 
     Example 20 
     The device of claim  19 , wherein the system further comprises means for performing one of the methods of examples 11-18. 
     TCAS computer  102  and/or its components or features, including AS SAP tracker  104 , TSAA system  106 , aircraft maneuver prediction unit  134 , and/or other components or features thereof, may include one or more processors. The one or more processors may comprise any suitable arrangement of hardware, software, firmware, or any combination thereof, to perform the techniques attributed to TCAS computer  102  and/or any of its components or features described herein. For example, the one or more processors may include any one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. TCAS computer  102  and/or its components or features (e.g., aircraft maneuver information  138 ) may also include a memory which can include any volatile or non-volatile media, such as a RAM, ROM, non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, and the like. The memory may store computer readable instructions that, when executed by the one or more processors of TCAS computer  102  and/or its components or features cause the processors to implement functions and techniques attributed herein to TCAS computer  102  and/or its components or features. 
     Elements of TCAS computer  102  and/or its components or features as disclosed above may be implemented in any of a variety of additional types of solid state circuit elements, such as central processing units (CPUs), application-specific integrated circuits (ASICs), a magnetic nonvolatile random-access memory (RAM) or other types of memory, a mixed-signal integrated circuit, a field programmable gate array (FPGA), a microcontroller, a programmable logic controller (PLC), a system on a chip (SoC), a subsection of any of the above, an interconnected or distributed combination of any of the above, or any other type of component or one or more components capable of being configured in accordance with any of the examples disclosed herein. Elements of TCAS computer  102  and/or its components or features may be programmed with various forms of software. Elements of TCAS computer  102  and/or its components or features as in any of the examples herein may be implemented as a device, a system, an apparatus, and may embody or implement a method of combining air traffic surveillance data, including for implementing example technique  700  as described with reference to  FIG. 17 . 
     An “aircraft” as described and claimed herein may be or include any fixed-wing or rotary-wing aircraft, airship (e.g., dirigible or blimp buoyed by helium or other lighter-than-air gas), suborbital spaceplane or reusable launch vehicle stage, spacecraft, or other type of flying device, and may be crewed or uncrewed (e.g., unmanned aerial vehicle (UAV) or flying robot). While some description uses the example of ADS-B radio surveillance data, other examples may use extensions or modifications to ADS-B, or other forms of ADS-B-like radio surveillance, or ADS-C or any kind of radio surveillance data, in any manner described in terms of the example of ADS-B data in the description herein. 
     Any of the systems of the examples of  FIGS. 1-16  as described above, or any component thereof, may be implemented as a device, a system, an apparatus, and may embody or implement a method of implementing a method for determining modified protection volumes, including for implementing example technique  700  as described with reference to  FIG. 17 . Various illustrative aspects of the disclosure are described above. These and other aspects are within the scope of the following claims.