Horizontal miss distance filter system for suppressing false resolution alerts

A system for suppressing a false resolution alert message from an air traffic alert and collision avoidance system, comprising:

• means for input of a surveillance range measurement of an intruder aircraft from the air traffic alert and collision avoidance system;
• range tracking means coupled to said surveillance range measurement input means for determining horizontal miss distances greater than a predetermined value using at least a second derivative of a predicted range of the intruder aircraft, said second derivative of said predicted range of the intruder aircraft being greater than a predetermined first threshold value, said range tracking means including maneuver detecting means for determining that the intruder aircraft is changing in either direction or relative speed and providing a maneuver indication output;
• and,
• inhibit means coupled to said range tracking means and the air traffic alert and collision avoidance system for inhibiting transmission of a resolution alert message responsive to said determined horizontal miss distance being greater than said predetermined value and an absence of said maneuver indication output.

A method of detecting that an intruder aircraft is maneuvering in an air traffic alert and collision avoidance system, comprising the steps:

• providing measured range values of the intruder aircraft at predetermined time intervals;
• calculating a predicted range value based on measured range values;
• calculating a third derivative of said predicted range value;
• determining an occurrence of a maneuver of the intruder aircraft responsive to said third derivative of said predicted range value being less than zero;
• and,
• inputting an indication of said determined occurrence of a maneuver of the intruder aircraft to an alert filter system for inhibiting said filter system from suppressing an alert message output relative to the intruder aircraft.

A method of suppressing a false resolution alert message from an air traffic alert and collision avoidance system, comprising the steps of:

• a) providing a measured range value to an intruder aircraft;
• b) calculating a predicted range value, a predicted range velocity value and a predicted range acceleration value based on said measured range value for a predetermined future time interval;
• c) comparing said predicted range acceleration value with an acceleration threshold value;
• d) if said predicted range acceleration value is less than said acceleration threshold value, proceeding to step (a), otherwise continuing;
• e) calculating a projected horizontal miss distance for the intruder aircraft;
• f) comparing said projected horizontal miss distance with a distance threshold value;
• g) if said projected horizontal miss distance is less than said distance threshold value, proceeding to step (a), otherwise continuing;
• h) determining whether there is a change in either of a relative direction or a relative speed of the intruder aircraft to identify a maneuvering condition;
• i) if said maneuvering condition is identified, proceeding to step (a), otherwise continuing;
• and,
• j) inhibiting a resolution alert message from the air traffic alert and collision avoidance system.